1987 300TD confusing running hot problem
 

1987 300TD running hot
Iposted this under general but I hope this forum will give a better response than the 0 i got in tech tips.
I have a 1987 300TD with 200K miles. About 15K miles ago the car over heated, into the red, because of low fluid level in the radiator that was leaking. Replaced the radiator, thermostat, hoses, and serpentine belt. Car contiued to run hot, at about 100deg C. with the temp fluctuating with load. This all began to happen after it over heated the first time.. Car gradually got worse and began to make lifter noise. Decided to remove head and do a vlave job and replace all the lifters. Also replaced water pump and visco fan clucth. Car ran much better but still runs hot with fluctuating temp. Oil cooler was swapped with another car. No change. Finalyl decided to change oil thermostat this weakend as a last ditch effort to solve problem. No change. Where is the next place to look? Also I changed the temp sending unit early on. It almost seems that the termostat opening point is off,but I have changed it twice. I have gotten so fed up that I feel like selling the car, but it runs well outside of this temp problem. Also ambiant temp has minimal effect on engine temp. It was 42deg F this moring and car still ran hot.

603 Temp issues?
 

Man I have the same engine in my SDL and I've been recently experiencing wacky engine temp syndrome. I've been searching and following a couple of threads here and they all seem to relate to cracked cylinder heads! Now of course I don't know but you situation seems like it fits. You said you had your head off to do a valve job, was you head checked at that time thoroughly for straightness and cracks? If the head wasn't right the new head gasket could fail and it seems like that situation is a precursor to eventual head failure from thermal stress. I hope not but its something to consider. I'm waiting for a tool to pull my head bolts and then the head for a look at the gasket and the head area between the valves. You can do a search for this 603 motor and cylinder heads to find an ongoing head failure/replacement discussion, Good Luck!:(

300sdl advice
 

Had the head off and pressure tested and checked for warpage. It was trua and flat and passed the pressure test. Did a careful visual inspection and the head looked great. I have no water loss or coolant loss that I would expect from a cracked head. The engine could run better when cold but I suspect it needs a can of diesel purge. THe engines runs well. I was thinkng it could be related to turbo functions or back pressure issues. I will most likely take it to the dealer and get charged to much for them to tell me they can't find anything.
Some advice on removing the head fromyour 300. I had a heck of a time taking the chain guide pins out. Be careful and do not strip them. Get all new plastic and rubber retainers for the injection fuel lines, they will break as you take the off. Have your exhaust manifold checked for warpage, my was realy warped from a leaky gasket on the no. 6 sylinder. Follow the directions carefully when taking the cam shaft off. Change your lifters if you hear any lifter noise, it made a big difference on mine.

Check the temperature of different sections of hose/radiator, etc.. and you should be able to at least tell if you are circulating hot water (thermostat is opening) through the radiator. If one hose is hot and the other hose it not then you have an issues in the circulation system. On my 240D I had to get the thermostat from a local parts house because the MB thermostat would not open.
I will say that the warmer/hotter weather we have been having has done wonders for both the 240 and the 300D.

1987 300TD confusing running hot problem.
 

May I assume that you had the Trap removed by MB under the recall program?

Camshaft timing is correct? Injection timing is correct?

You are using 50/50 mix of water and antifreeze?

Cooling system is properly bleed of all air....ran heater full on?

20-50 synthetic oil used?

Just a few suggestions.....

ebiker

1963 190Dc, rusted away.
1974 240D, rusted away.
1977 240D, the "money pit."
1981 240D, accident victim.
1985 300D, traded away, sob.
1987 300D, son of "money pit."
1991 Audi 100...good in snow.
1993 Audi 100S..grandson of "money pit."

1977 BMW R75/7, 'ol reliable.
1987 BMW K-100RS, fast 'n reliable.

Check the thermostat out of the car heat up some water to check at what tempture the stat. opens. Had to check several be for i found on that was right.

Bill

Thanks for all the suggestions. I had already done most of them, except the 20/50 synthetic oil. I have run Rotella T 20/50 for most of the life of this car. Seems to have worked, but I have considered running synthetic if I can't fix this running hot problem. It seems that changing the oil cooler and replacing the oil thermostat did have a minor positive impact. Still runs hot on load. What turbo component would make an engine run hot? I almost feel that the original thermostat had a different flow capacity than the current ones (I have put three new ones in ). THe car began running hot after I replace the original thermostat and over heated the car on the first run. Did not bleed the the air out of the cooling system correctly and it overheated less than two blocks from the house. Any advice before I take it in to the dealer?

Henry

If this were a Jaguar, I would say the head gasket was still leaking somehow...

That is still what it sounds like. Have you had the coolant checked for exhaust gases?

I am on thermostat #3 and this one makes my temp guage read 90C. It is a dealer thermostat. As a pessimist, I may conclude that this one opens early and is hiding a problem ;) Previous two Wahler t-stats read 98C on the freeway. Has you car ever had dexcool? Do you have brown sewage like material lining your connection from the upper radiator hose to the block?

Brian

How do I get the coolant tested for exhaust gas?

1987 300TD confusing running hot problem
 

Let's see, you replaced the thermostat? Only goes in one way...spring faces in, right? There might be a small "Bleed Hole"-faces up, I believe. Upon filling the cooling system with a 50/50 mix of MB antifreeze 'n water, did you jack up the front of the car to help bleed air, in addition to heater being on? Has the trap oxidizer been removed by Mercedes Benz warranty and replaced with the NEW exhaust system? Have you tried a bottle of Red-line water wetter? MB radiator cap is the correct one--important--use a Benz cap! Synthetic oil will drop the oil temperature a bit. I used Valvoline 20-50. BTW, if you had a cracked head into the combustion chamber, you would know!!

Good luck....please let us know the outcome!!

Ed.

(Ride a Motorcycle.....view bad driving first hand)

According to my Haynes manual. The thermostat starts to open between 175f to 193f(80 to 90c). The stat. is fully open between 193f to 200f(90 to 94c). My experience with overheating in other cars was the thermostat. Just try removing it completely and see what happens. If you have a jelly thermometer or frying thermometer, you can test it in a pan of water on your stove and see what temp. it opens and closes. Also sometimes hoses colapse if they are old, not allowing the water to circulate properly.

I had the opposite problem -- no heat. Fixed it with a new MB thermostat.

I'd never use anything buy an OEM thermostat -- all the aftermarkets I've seen don't work properly.

Normal temp is about a needle width above the 80C mark -- shouldn't go above that this time of year.

Replace the coolant tank cap with an MB 20 psi one. Some aftermarkets are OK, most are not (I had a coolant loss/high running temp problem with the 300TE due to a bad cap).

Otherwise, check for high coolant pressure cold -- if there is significant pressure in the coolant tank on a cold engine, the head gasket has blown or the head cracked :(. Usually there will be oil in the coolant, too if this is the case.

The only other causes I can think of are very fast IP timing (hard to set on these cars), a collapsed hose, restricted circulation of coolant (is it possible to get the head gasket on upsidedown?) or, the cheap fix A BAD SENDING UNIT!!!

I've seen more than one go bad when the engine overheated, reading high all the time. The one on my sister's Volvo pegged out after she blew the head gasket and toasted the head. I'm sure yours wasn't that hot (I had to replace the head), but they do go bad. Cheap to replace, too. Loose wire will do the same thing.

The Jaguar mechanic I use has a kit that checks the coolant, if there are exhaust gases present it turns yellow. I presume a MB mechanic would have a similar test kit.

Thanks for all the advice. Unfortunantly there is no smoking gun on this topic. Sending unit has been replace. Radiator is working well and there is no cold spots on radiator. No indication of exhaust gas in the coolant. Radiator cap has been raplace and changed with a 300sdl cap. No collapsed hoses. Water pump, fan clutch, oil thermostat and oil cooler changed. Good power. Is it possible that for what ever reason, I keep getting the wrong or a bad thrmostat? Every indication would point to the thermostat but I have changed it three times, all with Behr thrmostats with a green dot on it witch signifies turbo diesel. Maybe there is a conspiracy to trash a buntch of 603 engines. I plan on drilling a hole in the thermostat to increase flow prior to removing the thermostat all together. Any last minute suggestion? How many holes and how big? I figure to increase the CV of the thermostat by 30 to 50% if possible. A mechanic told me he did it once on a 450 to take care of a nagging overheating problem on that car. Maybe it has something to do with turbo operation or some seemingly dissassociated system. Maybe the car has an attitude problem or suffering from PMS, (Pre mortem syndrom)

Henry

The two I had where Wahlers, then I bought a genuine MB t-stat and the car runs cooler. Could be a bad batch if you've bought them from the same supplier. Try a different supplier or a different brand.

Brian

Check the injection timing, and look for a bottom radiator hose collapsing under high flow conditions -- this restricts flow at speed and load, causing overheating.

Double check the thermostat installation -- I know it is a pain in the butt, and it something is restricting the valve opening, it may work fine and still not open all the way.

Do you have any pressure in the cooling system with a cold engine? If so, you have a cracked head or leaking head gasket.

Other than that, all I can think of is a flow restriction somewhere, and I can't think of a quick way to check that -- no cap on the rad.

Peter

Peter - I think I am finally going to break down and pull the head on the 300D over the next couple weeks. It keeps pressure in the coolant reservoir a day after shutting it down from the day before (the 240D does not do this, neither does the Honda or E320). The 240D is running great (with a new front windshield and rear window seal as of this week and a new paint job scheduled at the end of April) so I am going to bite the bullet and see what the top end of the the 300D looks like. I am VERY reluctant to pull the head on a good running car but what the hey. I am "caught up" on my projects for right now so this looks like a good one. I will post pictures if I find anything worth showing.

Henry,

You still have not answered Peter's question: Is there pressure in the cooling system when it is cold? In the morning, before you start it, squeeze the upper radiator hose. It should be SOFT, or even collapsed under vacuum. Open the rad cap, it should not "pop" as if there is pressure present. If all that is AOK, go drive the car HARD - lots of full throttle runs to the redline. DO NOT open the radiator cap. Now repeat the same test the next morning - there should still be ZERO pressure in the system. If there is pressure (upper hose tight, cap "pops" when you remove it) then you will need to pull the head (again). I just got done doing this on my car (search this forum for topics posted by me in the last 2 months).

Forget messing with the thermostat. I have read over and over where people go through 2, 3, 4 or more with this kind of problem. It ain't it. Don't drill holes in it. And do NOT remove it! Mercedes designed the car to run with it in place, when you remove it, very little coolant is sent through the radiator - meaning you could overheat it AGAIN. I'm assuming you have either a dealer t-stat or a decent German made one, correct? No "Made in China" stuff from McParts?

Oil - running synthetic is great, but should have absolutely NO effect on this problem. Your car should run at 85-90C regardless of oil. You are trying to kill a mammoth with lawn darts here. Last question - how old is the radiator? And is it an OEM aluminum Behr? I had one plug up and cause serious hot running and it was only 3 years (and ~40kmi?) old! Changing it cured my problems (along with a new fan clutch), now the car refuses to run over 100C even in 110F ambient temps, freeway OR idling. Normal winter temps are 85-90C on the dash gauge.


I still think you have cracks in your head that were missed in the "presure test". Was it magnafluxed? Anyway, check out photos of my head replacement job, and the cracks in the head (cyls 5 & 6), here:

http://www.meimann.com/images/mercedes/head_gasket/


Keep us posted! :)

Dave, With all due respect, why can it NOT be the thermostat? My 1987 300D ran one needle width below 100C (98C) in 39F weather on the freeway before a new radiator and after. I boiled my first and second thermostat's (Wahlers) and they opened and closed at the same time. With a third thermostat the car immediately ran at 90C and only gets to 93C a low speed with heavy load.

How does one check the lower rad hose under load to see if its collapsing? My upper rad hose used to collapse so I purchased a new expansion tank cap and the problem went away. I replaced the upper rad hose just to be safe. I plan to replace the lower rad hose soon, to be safe.

Brian

running to hot
 

acts just like mine did when i got the stat in backwards. Bob se,ks.:D

Brian, it's just *highly* unlikely (IMO) that you'll get multiple "bad"thermostats. You said the first two (Wahlers) operated the same. What brand is the third? A miscalibrated aftermarket unit could be masking a more serious problem if the first 2 units were good per MB specs... i.e., you got the needle down, but is there something else wrong? I installed a Wahler in my sister's 1987 300D recently and it runs at 85-90C all the time. If you got a 3rd Wahler that changed things then that leads me to believe we shouldn't be using them, now should we! :eek:

Another note: Theses cars (1987 300D) are VERY finicky about filling with water fully. It helps to jack up the passenger side as high as you can when filling. Then run the heater on "high" until you get hot air from the vents, and keep an eye on the gauge. Often it will cross 100C before the t-stat opens and the air pocket gets purged, then it drops to normal (85C). Also, I once had trouble for weeks with the upper hose collapsing when it was cold. Eventually it went away, I think there was an air pocket that finally worked itself out. There was no problem with cooling, just the hose visibly flattened (when cold).



Um, Bob - it is impossible to install the t-stat in this engine backwards. It only fits ONE way. You cannot fit it into the housing the other way. Trust me. :p


Regards,

Dave, the third thermostat was a MB dealer thermostat. Yes, it could be bad and opening too soon. I'm trying not to be pessmisstic. I keep an eye on the coolant expansion tank and hoses and the level hasn't changed nor have any hoses collapsed. I was able to put back the amount of coolant I took out. In the past I have gotten only 1/2 in, knew there was an air bubble and was careful to not overheat the car while adding the rest of the coolant. I haven't tried jacking up the car yet, but next time I will give that a shot and make sure the heater is on max too. I figure that 90C is halfway between 80C and line between 80 and 120.
Brian

Jim:

I just passed on a 1980 300D with a leaking head gasket that caused cooling system overpressure and eventual overheating -- leaking compression into the cooling system from one cylinder.

That wasn't a problem, but the floor was rusted through on both sided and the driver's side rear fender was perforated in a couple places -- I already have a rustbucket, I don't need another one!

I assume you have replaced the radiator cap with a new factory one and are still having the problem. If so, you may very well have a head gasket going -- not a big problem if you've got a helper to haul that head around -- it's heavy!

I'm also going to look at a 1980 300D (listed at $1900) in the next week or so -- I think I'm about to become an independent contractor and will need a cheap transportation device.

Peter

Yes the radiator, water pump and radiator cap are new and the car runs out great. It does have a single "miss" on cold start up after it has been sitting for a week or so but I feel that may be an issue with the valve adjustment (it is time) or the fuel filters. I will say that it runs slightly cooler (based on the gauge) than the 240D - especially on the interstate. On the 300D the needle NEVER gets over the top edge of the 8 on the 80 number.
Before I pull the head - just for the heck of it - I think I will swap the radiator caps on the 240D and the 300D and see what happens.

I took a look at the photos and re-read all the threads. If the head was cracked, it did not show up on the pressure test. The head was not magnefluxed. I wish I had it done. I was not aware that magneflux would work on a non magnetic metal. I just went out to check if the cap was pressurized when it is cold and it gave a slight whoosh sound when I opened it. I will perform the run hard test and check it again in the moring. I do agree that removing the t-stat is not the answer and I hope i did not spend money on the valve job for not. I do now that I did check the head for cracks very carefully and I can say that I had no cracks as is shown in the photo's. Is it possible that the cracks are intergral to the head and not visible? I will bleed the car as you recommend and see what happens. I will let everyone know the outcome.
henry:confused:

I forgot to mention that the radiator is 6 months old and it is a Behr aluminum radiator. All parts are OEM with the exception of radiator fluid. That can not be the problem. This car never ran hot until I overheated it in conjunction with a poor bleed job after I replaced hoses, radiator and t-stat.

henry

Hi Henry,

Hmm, this is all very strange. Be careful you're not reading more into the "whoosh" sound than is really there. The more definitive test is the radiator hose. It should be quite soft when cold. When there is the high pressure problem, it is so tight you can't squeeze it together (to make the opposite walls touch) unless you're Schwarzenegger or Stallone. ;D

On my car, with the high pressure, it's not a gentle little "whoosh" sound. It's more of a "POW!" when the pressure releases. If you have little to no pressure when cold, your head & gasket are probably OK. And in that case I'm low on ideas, it sounds like you're replaced almost everything possible!

Have you checked the dash gauge, to make sure it's reading properly? A new sender wouldn't cure that...!


Regards,

Dave, thanks for the advice. I agree with your "woosh" analogy and I will pay more attention to the hard or soft hose approach. No one has mentioned the auxilary fan. It seems to never come on. AC on, off, engine temp hot cold, never comes on. What turns it on? I will check the temp gauge in the dash. I recall reading in the manual a procedure to test it.

Henry

Hi Henry,

1- I just thought of something else, although it's highly unlikely given the timing of your problem. Have you cleaned out your A/C condensor fins? The radiator should be clean since it's almost new, but the condensor could be filled with bug guts & other crud, drastically reducing airflow to the radiator. High pressure water from the local car wash works good to flush it out, and/or compressed air. It's preferred to do it from inside out but that's a real PITA.


2- The aux fan is another interesting story. First, let me say that it's not your problem. The car should run cool regardless of the aux fan. It is there for extreme heat conditions and to help the A/C cool better, not for "normal" engine cooling. It has 2 speeds. The high speed only engages from the 3-prong temp switch up at the water neck, by the upper radiator hose. It is supposed to turn the fan on high at 105C. The low speed only engages from a switch on the A/C receiver/dryer. This turns on when the refrigerant high pressure reaches a certain pressure. There are 2 different switches. Older cars, like yours, have the green switch - which is rated at something stupid like 20 bar, so the fan almost never runs. Later cars (1990-up?) have a red switch, which engages the fan at a more reasonable 16 bar, so the fan runs most of the time the A/C is on. You can retrofit yours to the red switch, BUT you have to evacuate & recharge the A/C system, which is a PITA (and expensive). You can verify the fan itself by shorting the two pins on the 105C temp switch, this should make the fan run on high. Shorting the leads at the green (or red) switch will make it run on low. There's also a relay in the circuit, so if the fan doesn't work, check the fuses and the relay.


HTH,

1987 300TD confusing running hot problem
 

OK, first of all, if you have a cracked head--combustion chamber into cooling system--you will know!! As you drive the car, You will lose all of your coolant. I have been there, to the tune of $2,800. (Rebuilt head). If you have a slight combustion leak into cooling system, you will see bubbles in the coolant. Diesels have 22:1 compression ratio. The Mercedes Benz radiator cap is rated at 17PSI for the 87 300D. But, do check with a dealer on this. I had suggested MB antifreeze because of the aluminum parts. The auxillary fan cuts in at coolant pressure of 20-Bar. It's also affected by coolant temperatures of 110-C. Of course, relays and switches control this operation. Temperature sensor could have overheated and thus become faulty when the motor overheated. That sensor is B11/7, it's up by the fuel filter. Finally, I assume that the Mono valve and the auxillary circulating pump are good. I wish that I could offer you more help.

Ed.

Um, Ed... it is possible to have a cracked head and not lose coolant. You will lose coolant only after the crack becomes extreme. Initially there may not be any coolant loss. I just replaced my head too, cracked in 3 cylinders, and I had no coolant loss - just high pressure when cold. Search for other threads in the last 3 months on this subject. "Bubbles" are not visible or present - just abnormal pressure.

Also, the radiator cap is rated at 1.4 bar, which is roughly 20psi - not 17. And the aux fan operates as I stated in my previous post - NOT as you describe. If you study the W124 Electrical manual for the 1987 300D you will understand. And as I stated before, the aux fan operation will not have anything to do with Henry's problem. The car will stay cool enough without the aux fan under normal (i.e., non-Death Valley) conditions.

Oh, one more thing: Sensor B11/7 is only used on the 5-cylinder diesels from 1990-up, it is a preglow temp sensor. The 1987 model has a different sensor in this spot - B11/4, which is for the EDS (Electronic Diesel System). The 1987 model has no external preglow temp sensor, it is built into the preglow relay (senses ambient temps only, not engine coolant temp.) This would not affect the cooling system, ditto for the monovalve, and aux coolant pump (which only helps keep hot water in the heater core at idle, when the water pump doesn't provide enough flow there.)



Regards,

1987 300TD confusing running hot problem
 

Well, let's see now, Dave M. As I pointed out, my 87 300D cylinder head cracked in the COMBUSTION chamber resulting in an entire loss of coolant within a few miles. I was driving the car @ 75mph when this occured. Later, at the MB dealership, the technican poured water into the cooling system, I started up the motor and water shot up out of the expansion tank. That 22:1 compression has to go somewhere!
The MB maintenance manual cooling system test specify's a pressure test of 1.0-1.3 bar. Of course the rest of the MB maintenance manuals, (3) could contain more misinformation, too.

Your right, Dave.

After 12 years and 177K of owning my 1987 300D I'm wrong.

I'm outta here!

Ed.

Ed, like I said - yours is the extreme case. It is possible to have minor cracks without coolant loss. See photo below of one of the 3 cracks in my head, with NO coolant loss. I think you missed the early warning symptom of high pressure when cold.

Now, about the pressure ratings. Section 20-017 of the OM603 engine manual states that the cooling system is to be checked by pressurizing to 1.4 bar. Also, section 20-430 states that the original 1.2 bar radiator cap has been superceded to a 1.4 bar cap, the 1.2 is no longer available. I'm not sure what the "maintenance" manual is. There are 2 chassis manuals, 1 electrical, 1 climate control, and 1 engine manual, and the Technical Data Manual. I have all of the above and also the Mercedes 124 CD-ROM, which has a "maintenance" manual section, which just outlines what items to check at particular intervals, IIRC- not actual service procedures. I'm not pulling this stuff out of thin air, really! It's all in black & white. And yes there are errors and contradictions in some of the manuals, particularly the electrical manual. However if you compare different sections you can determine which part is correct. :cool:

Update : I just checked out the 124 CD-ROM to see if I missed something. It appears that the Maintenace Manual has more in there than I recalled (oops). However, it is a generic manual for all Mercedes models, not just the 124 chassis. The section on testing the cooling system does spec 1.0-1.3 bar, but that is for chassis 107, 123, 126, and 201 (up to ~1985). None of those cars used the OM603 engine. The OM603 engine manual does spec 1.4 bar for test purposes. FYI, the newest MB's (210 chassis, I think) have some engines with 2.0 bar (~29 psi) caps! Wow... that's high pressure. :eek:


Regards,

And here's a pic of the crack in cylinder #6. The third crack was almost identical to this one in cylinder #1.

Finally pulled the head - started another post. Based on what I have seen so far I suspect I had a tired head gasket, maybe just trying to justify pulling it off :).

The saga continues.

I checked to see if I had pressure in the coolant system this morning. Nada, zilch, just soft hose and no pressure when I removed the cap.

Having nothing better to do today I decided to take out the t-stat and check it with the spare MBZ t-stat. I had forgotten what a PITA it is to remove them. That top bolt is just out of reach of the socket and I could barely get my finger on it. That coupled with the goofy routing of the line to the expansion tank just seems to get in the way. I was so temptemted to remove the air supply duct but I also remembered how hard it is to get it back on around the sheet metal heat shield. Anyway, got it out, checked in hot water. Both opened at about 176Deg F and where fully open at boiling. at least I guess thay are. No real way to tell if they can or should open more. I wish the manual had some measurement info on the t-stat operation. So two good t-stat's. Went back to the MBZ one. Car still runs hot. On the power run at 85mph, with ambiant at 63deg F. the temp gauge went up to a needle width of 100deg C and on the hills sneaked ever closer. I am truly confused. I can only assume that the head has some minute crack that was missed on the pressure test and it is not contributing to coolant loss or system pressurization or I have some strange back pressure problem on the exhaust. The timing on the car seems to feel right. That is what I will checked next. I recall the manual has some test that was done to check if the trap was plugged. Glad that there is no trap on this car. Or what I would like to think is that the original t-stat in the car was different than the ones currently available. (I must remember, NEVER THROW ANYTHING AWAY)

I would guess that timing issues that would cause the car to run hot, would also affect cold starting and power. this car has none of that.

Did a search on the running hot problem and this seems to be an issue for a bunch of these cars. Also, there is a lot of dicussion about bleeding air out of these engines. I remove the top hose from the radiator and pour in the fluid until it starts to spiil out, then fill from the expansion tank. Then set the heater on high and let the car get warm. Seems to work. I do miss having a cap on the radiator.

henry

Henry,

If your hose is soft your head is probably fine. I doubt it's cracked. I know it sounds crazy but I suspect your "new" (6-mo old?) radiator. Is there any way you can get a different (new) one to test? Marshall Booth (MBCA Tech Advisor) pointed out that if the last one plugged, the system should be cleaned BEFORE installing the new one, or residual crud may plug up the new one ASAP resulting in the same problem. Did you do a citric acid flush at any point? Your t-stats are OK too. (BTW, a tip to ease removal is to yank the temp sensor in front of the housing - makes it a LOT faster too!) I also doubt you have air pockets, as long as you are getting 2 gallons back in after draining. Timing, as you say, probably isn't it either. Wouldn't hurt to check though. Did you ever check the A/C condenser for crud? Is it nice and clean?

Not to confuse matters (any more than they are already) but my car was running a few degrees warmer than it had been last night (and it was COLDER 40F) so I let the car sit overnight and check for coolant pressure in the AM - YES :( Wheeled straight into mechanic this morning asked about coolant hose should be able to touch sides together, "yes" was answer. Said I couldn't do it, eyes light up was his response. He seems to only have seen diesels with head that have REALLY cracked because he said you go down the street and you are done. Will find out more on Wednesday when it gets some new A/C parts. The odd thing is that it WAS running 90C steady at first and then seemed to over a few days get a little warmer.

If I had a small head crack (could is be as simple as a bad gasket?) what are the chances of it getting worse? Should I just leave it? The car never goes past 98C, its basically the same as HGV's right now.

Brian

Brian,

Yes, it could be the head gasket. But given the history on this engine (OM603.96x) it's more likely to the the head. The only way to tell is to pull the head and check. Maybe you'll get lucky! :D

As to whether you should just leave it, it's up to you. I bought a car with this problem last August, and have driven it 8kmi since then. It had lots of oil in the coolant tank at the time. I flushed it out, tried K&W Block Seal (no luck), and have been driving it anyway. I don't have oil in the coolant anymore but I get high pressure after one full throttle run to 60mph! All winter the car ran at 82C on the gauge, almost never budged over that. Yesterday it got to 85F or so and I had the A/C on. The temp would fluctuate between 85-98C, which isn't *that* hot, but it should move around as much as I saw. Last fall when I bought it, I noticed that heavy load when warm would raise the temp FAST. My other (good) 300D does not have these fluctuations. I plan to yank the head in the next few weeks (been finishing up my other cars first).

So yes, you could drive it for quite a while like this - just be aware that it could be a ticking time bomb. Watch the temp gauge VERY closely, especially when the weather gets warmer and/or you start using the A/C. I know another guy with the same car (1987 300D), with similar symptoms, who is also driving it - with no head removal plans. When I do pull mine I'll be taking pictures and posting my findings here, so y'all will know what happened...

:cool:

Yes, I did check the condenser and it is clean. I also changed the radiator with a new one and it had no impact. I will drive it until it gets in the red then I will attack it again. I will put some wet water stuff in it and see if it makes a difference. Until then, I have given up on this one. Will continue to keep a close I on pressure in the hoses and check for oil in the coolant.
What temp should this car run at and when whould I worry?

Henry

Normally it should be 85-90C. In summer with A/C on more like 90-100C. Anthing over 100-105C isn't normal. The "Worry Zone" is 110C and higher.

At 120C you better turn the heat on full and/or shut off the engine ASAP... :eek:

Well I went out and bought the water wetter and I have a 300 mile road trip up to the Geysers in California. There is one long 18.5% grade that I have recently ended up with the heater blasting and all the windows open. I will see if this does the trick and report back. Thanks for all the advice.

I was also looking at running synthetic oil, but at $40 every 5K miles it seems pricey. What is the upside? Can you spread out oil changes?

I have always specified synthetic oil for rotatiing equipement that must run 24/7 for 12 months at a time. This is what it was it meant for. It seems that if you can change oil on a regular basis, it does not warrant the cost.

Am I all oily behind the ears?

henry

Henry,

First, using synthetic oil won't solve your hot running problem. :( With that said, yes, you can run an extended drain interval when using synthetic oil. Assuming you don't operate the car under "severe service" conditions (i.e., mostly city driving, stop & go) you can push out the oil changes to 10kmi easily with most any synthetic (Mobil 1, etc.) Beyond that I wouldn't do it unless using diesel-specific synthetic - Mobil Delvac-1, Shell Rotella Synthetic, Amsoil Diesel, etc. These are specially designed to handle the extra soot that will develop over the longer interval. Delvac-1 is one of the best out there, the Amsoil is good also. The Shell stuff is new and unproven but should be OK too. Using these, maybe 15-20k would be possible, especially with lots of freeway driving.

The only way to verify the "safe" limit is with an oil analysis, which is available from numerous sources. I use the Mobil Delvac AccuTrack "extended drain" analysis, it's $13 for the kit (plus S&H both ways, figure ~$20 total per analysis.) I am using Delvac-1 oil, changing the oil every 10kmi, and changing the filter every 5kmi. My oil consumption is 1 quart per 7500 miles or so. The oil analyses (sp?) shows that at a 10k interval everything is peachy. I could probably go longer, but I only put ~10kmi per year on the car so I figure an annual $45 oil change isn't bad. I drive a mix of city & freeway miles. If I drove all freeway I would change it at 20kmi (assuming the analysis was OK.)

Other benefits include lower oil temps, marginally lower coolant temps, faster cranking, faster cold oil pressure building, faster cold starting, less wear on startup, higher "safety zone" under extreme operating conditions, and some other things I can't remember right now. I've heard (Edmund?) that using synthetic ATF helps lower coolant temps a hair as well, since the ATF cooler is inside the radiator. I plan to switch to Mobil-1 ATF at my next tranny service (21kmi and 11kmi away on both my '87's, repsectively.)


Good luck,

I have been waiting to let everyone know what the results are of everything I have done to the car and how it is running. I have replaced every possible component of the cooling system and have come to the conclusion that as long as MY car does not overheat into the red, I will live with the results of my labor. I went up to Tahoe on monday at a sustained speed of 70 with an ambient temp of 75-80 deg f. The car ran between 95 to 110deg C. This is hot but not overheating. On the return trip going through Sacto with AC on and ambiant at 85-90 deg F, the car ran about 90-105 Deg C. For me this will have to be acceptable. I also got 26.5mpg on the return. Car burns about 1qt/1500miles and I can live with that. I do admit that the car runs hotter than before, but I will have to life with that akso. My car has 203000 miles and if I can make it to 300k, I will drop in a factory rebuild. I put about 30k a year, so maybe if I am lucky, I will put a new engine and go for my 500k badge.

I have finished the head job on the 300D and today was the first day I have driven any distance so I will pull the radiator cap around lunch today to see if there is still any pressure. I did drive around town day before yesterday (about 10-15 miles) and when I returned home removed the radiator cap and there was not any pressure to speak of although the engine was up to operating temperature based on the temp gauge. The temperature did not get above around 90-95 dC on the freeway run into work this morning (75 mph). Car runs great although I do have some fuel leakage issues that are causing a little idle roughness during the first start up in the mornings. I will get these issues resolved this weekend.

For those of you with to much time on your hands, try the following:
Remove the temp switch that is located on the t-stat housing and install a temp sending unit. It looks like it should fit. Disconnect the temp sending unit on the cooling water return line near the fuel filter. Run both leads into the passanger compartment and attach to a switch. Then run the leads of the switch to the temp sending unit lead. Drive the car until it reaches normal operating temp and toggle the switch between the temp sending unit on the cooling water supply and return. THis will give the temp rise across the engine. This will give the true status of the performance of the cooling system. Do this on a hot car and one that runs normal. Once a base line is set for temp rise accross the engine, use this as a bench mark. IN conjunction with this test, attached a T fitting in the line on the air bleed line at the expansion tank, and run a tube into the passanger compartment and attached a 0-20psig pressure gauge. Then calculate the vapor pressure of the glycol and water mixture in the cooling system and compare it to the actual running temp vs. pressure relationship. If it is higher than the predicted value, this would indicate a leak from the engine into the cooling system. It should always run below the relief pressue of the radiator cap and within the pressure temperature relationship of the fluid. Remember the Molier diagram?

For those of you with to similiar cars, you can always check the temp gauge accuracy by cross connecting the temp sending unit from on car to the other. Make sure both cars are grounded together and compar ethe readings. As important as the cooling system temp is the oil temp. Have not figure out how to test this. But just give me time.

SO who is up for the challange?

Henry