Strange cooling system problem - exhaust gas entering system??
 

Hi all,

My 1987 300D developed a strange problem suddenly. The cooling system remains under high pressure even when stone cold (left overnight). Yes, I have replaced the radiator cap. The car has never done this in the previous 4+ years I've owned it. The only way I can think of abnormal pressure in the cooling system would be from exhaust gas entering. How do I test if this is happening? The coolant looks clean and smells fine (to me.) There is no oil in the coolant or vice-versa. I suspect either the head gasket or a crack in the head (shudder.) I'm at a loss here... Help!


Dave M.
Sacramento, CA
1987 300D - 228kmi (weird cooling system problem)
1987 300D - 234kmi
1984 300D - 205kmi

exhaust gas in radiator test
 

Hi GSXR: Before I bought my 500 sel, I was leary of owning an aluminum engine, cracked heads, etc. So I convinced the owner to let me take the car to a smog shop in San Diego and they put the probe that they normally check emissions at the opening to the radiator cap and it will sniff any exhaust you may be getting from a cracked head, etc. Hope this helps, woody

The way you discribe,things it dosnt sound as if your car has a problem.It sounds as if the radiator cap you replaced is just doing its job well.

My '87 300D holds radiator air pressure a long time.

If you are not losing any coolant, I can't imagine you have much of a problem. I think your cooling system is just doing a good job now at holding pressure.

Ken300D

Hi Ken,

The problem is that about 12-24 hours after the engine is shut off, the pressure forces coolant out somewhere near the water pump or thermostat area - I can't tell exactly. (I'm guessing the water pump seals.) When the engine is hot it doesn't leak. I'm speculating that when the metal w/p body cools, the seals shrink a tad and allow seepage. After all, the system is designed to hold 1.4 bar at full operating temp, not at ambient. If I find it is coming from the w/p I'll probably replace it anyway.

However, I don't feel the real problem is the leak (although that's not good), I think it's the fact that there is high pressure when cold - which is NOT normal! Usually, when the engine cools off the system is under slight vacuum. The upper radiator hose may even be "compressed" a little bit - but there is NEVER any pressure present when cold.

Almost the entire cooling system was replaced ~3 years ago - new radiator, water pump, fan clutch, thermostat, all 5 hoses in the engine compartment, new plastic reservoir/tank, radiator cap, and factory MB coolant installed w/RedLine Water Wetter. It's been doing great up until a few weeks ago.


[Side note: This proved the dealer to be totally wrong in their claim that "if it's not in the red, it's normal operation." What a load of crap. The car used to run at 105-115C in the summer, and after replacing all the above it now refuses to ever exceed 90-95 except under the most brutal conditions (i.e., 110F ambient, climbing a hill with the A/C on). The problem in my case was a bad radiator AND a bad fan clutch. I changed the other stuff as preventive maintenance. My experience with several other 1987 300D's is the same - they should never get over 90-95 most of the time, and 105+ indicates a serious problem.]


Dave M.
Sacramento, CA
1987 300D - 228kmi
1987 300D - 234kmi
1984 300D - 205kmi

I have had cars over the years that when cold still had pressure.

I know, I've heard that from other people too. My point is that this car NEVER, ever did this until recently, and my others don't either. I'm not talking about a little pressure, I'm talking about a LOT of pressure; 10-15psi or so. The cap almost shoots off the top of the reservoir when I loosen it. That's not normal.


-DM

Head is cracked
 

No doubt about it, crack in a combustion chamber. Extreme pressure in that engine forces gasses into the cooling system, the crak has not gotten large enough to allow coolant to be forced back into the cylinder, not yet.

All cooling systems should not only drop pressure from hot to cold but will actually develope vacuum when cold.

sorry for the bad news.

Mark, that's what I was afraid of. I'm hoping it is the head gasket and not the head itself. I'm probably going to try K&W Block Seal before tearing into things too far - it worked last time (to stop an oil dribble into the coolant, 3+ years ago) so who knows, it could work again! If not I'm in for a $1-$3k repair. Ouch... too bad the rest of the car is pristine, and I'll have to actually fix it... [;-)

I think people are confusing what happens with a conventional US car (unpressurized) coolant overflow tank vs. the Mercedes pressurized tank. In the US system, the car burps fluid out under pressure into the overflow tank, then pulls it back when cooling off. The Mercedes system is simply a radiator with part of it (the plastic tank) being "see through". In the US system, there is not supposed to be much air in the pressurized area. In the Mercedes system, there is significant pressurized air inside the system.

Since people that have this engine are telling you that this is normal, and you also indicate the radiator cap is now new, maybe what you need is a new water pump and not a new head?

I know the dealer will not be as happy........

So, we should get more people in here that actually have a 603 or 602 engine to tell you their experience. Maybe we both have cracked heads (in the engine). :)

Ken300D

On my 300D that coolant reservoir seems to stay pressurized for at least 24 hours after shutting the car down. In all honesty I have never seen anything like it and have pretty much come to the conclusion that it is normal.
I do not see any indication that I have an engine problem. Car starts and runs good and maintains level in the reservoir and I do not see any oil residue that would indicate a problem.

What an intresting post. Sure am glad it is not my car though!

Unfortunately, I agree with Mark Elrod.

Starting with a cold system, no pressure, and run it as hot as you
like, once it cools it will return to the same volume.

As Ken rightly states, the MB system keeps all of the coolant under pressure, and accounts for the natural expansion by
the elasticity of the plastic resivoir in the loop.

The only way the pressure could increase to something greater then what was in the system on startup is if there was a leak adding pressure.

Craig Amos
1987 300D turbo
270,000 miles

Thanks, Craig. That's what I think too. I'm really puzzled by the number of folks who say their systems hold pressure when cold - I posted to the MBZ.org diesel email list and got similar responses over there. I'm not sure if they're confusing the "rushing air" noise when opening the cap to be pressure instead of vacuum, or if there are a bunch of other 602/603 engines that are all going to need head gaskets soon as well! :)

Anyway, follow my logic here if you will:


The cooling system (602/603 engine specifically, but should apply to almost any engine) is a sealed system, with the radiator cap only acting as a pressure relief valve at 1.4bar (~20psi). When it's cold (ambient temp, 50F at my house) if you open the cap, there will be zero pressure in the system. Close the cap - same thing, zero pressure. Drive the car - the coolant gets hot, and expands, which causes pressure in the system. Shut down the engine, it cools, the coolant contracts, it returns to ZERO. If it doesn't there is something entering the system. If there were a leak, it would either lose coolant, and/or not hold pressure in the first place!

To explain how vacuum can exist, picture the pressure relief valve (rad cap) opening when the engine is hot, and releasing some pressure into the overflow tank. When the system cools, there will be less coolant in the system, which will result in slight vacuum. As I said, this is how my car acted for years prior to this month.

I'm going to try the K&W Block Seal route before tearing into the head job. I'm almost afraid to ask the dealer for a quote on the job. Any comments on things to replace while it's apart? I was going to have the timing chain & valve lifters changed, wasn't sure if there's something else I should add to the list...



Thanks again,

Dave M.
Sacramento, CA
1987 300D - 228kmi
1987 300D - 235kmi
1984 300D - 206kmi

An additional source of air pressure is a certain amount of liquid water boiling off into water vapor and that water vapor is contained in the relatively large air pocket in the pressurized recovery tank.

When the system cools off that water vapor does not fully condense back into water - therefore some residual pressure.

No matter what creates the pressure, whether water vapor, heat, or leaking exhaust, it won't get any higher than the release value of the radiator cap. So, you will always have the same pressure in the cooling system at engine shut down (given a reasonable period of operation in which the system heats up fully).

So my theory is that the reduced volume of the coolant when it does cool down is not sufficient to "draw down" the large pocket of pressurized air in the recovery tank.

So, with a non-leaking Mercedes coolant system you get residual pressure. It is a unique feature of the design that keeps the "overflow" tank pressurized. Being used to the unpressurized American/Japanese overflow tanks, I was a little startled too when I took the Mercedes radiator cap off the "recovery" tank the first time.

If you had a small exhaust leak that was pressurizing the coolant system, it still would not pressurize the system beyond the radiator cap rating. And we know a non-leaking system holds that pressure even when cold. I say its just water vapor, and drive on.

--------------
OK. It's not like my theories don't get shot down sometimes. :)
--------------

The whole reason I got the '87 300D so cheaply is because the Mercedes dealer had the owner primed for a head replacement when all it needed was one glow plug - so he dumped it at a "quick sell" price. I guess the dealers just see dollar signs when these engines come in with any issue - because they know its an easy $2-3K. It's an easy shot, "Oh yeah, ALUMINUM head, yeah that needs replacing......." :)

Ken300D

Easy test. With the engine cold remove the cap, then start the engine and let it run. Once warm give her a little throttle, not much just a little. If coolant starts running over through the neck on the tank, chances are good your need a head gasket (or head). If nothing happens hmm...nothings wrong. I don't think the water pump will circulate hard enough to flow out the expansion tank on this system.

I had a similar problem with my 603 motor. The system held a LOT of pressure, sometimes for days. Turns out I had a cracked head. By the time the new head, gasket, valve job, etc were installed, I was looking at a $5k repair bill.

I hope you are not in the same boat, but if you are, just remember once it's fixed, it should stay fixed for a LONG time.

Best of luck!

I've replaced the water/ethelene glycol antifreese mix to Evans waterless antifreeze in my '87300SDL. I costs about $25 a gallon but I think it is worth it. Since it doesn't boil until 375F, yes three seven five, there is no pressure needed in the system to keep it from boiling. To keep the pressure to zero, just leave the cap loose.

This makes water pumps, hoses, radiatores, heater cores ETC. last much longer because the are not operating under pressure and the waterless anti freeze is not corrosive to anything like a water/antifreeze mix always is. It eliminates the need for frequent anti freeze changes so in the long run may cost less.

P E H

wow PE - do you really leave the cap loose?

Crack in Head...
 

How would a vehicle owner Prevent a crack from happening?

Cracked Head
 

Usually......it indicates that the engine has been run hot. This may have occured MANY miles ago and the fatigue has just now took its toll. Loose head bolts can create the same problem, and a leaking injector can shock the head, especially in a diesel.

Then there is always the "it just plain got tired".

New heads are expensive, but far cheaper than another car and will last a LONG time.

Note here, NEW head, if it is temperature or age fatigue, a repaired head will last less than one year. The repair may be great, but the rest of the head is fixing to go.

Good Luck.

(Been there done this have the tee shirts.....)

Oil dribble into the coolant in a bad head gasket most of the time. I'm watching mine (on a trip to Florida this week) to see if it is still collecting or just left over from when the rad blew (new rad when I got the car).

If Block Sealant fixed the oil leak, the gasket sealed enough to prevent the oil leak, but is now to the stage you need a new gasket.

I've heard the Elring gasket is a problem, use the other suppiers (name forgotten at the moment!)

The original head was a problem -- warped even in normal use, and cracked when overheated, sometimes without overheating. Replacement is MUCH better -- all rebuilt motors come with new head.

Peter

In a truely 'closed' system, if you have zero pressure at certain temperature and you vary the temperature, you will get expansion and contraction and whenever the system returns to that zero pressure temperature, the pressure will ALWAYS be zero. If in real life it does not adhere to these thermodynamic laws, then you don't have a closed system. There is a leak somewhere.

I am suprised to hear of so many others out there who also have this as normal operation. I'd be curious to hear what the cooling system engineers at work would have to say about this.

Tell me more about this Evans waterless system.

If you have a leak at the water pump, fix that before assuming a head gasket problem. My guess is still a head gasket, but I'd replace the water pump first. Big pain, ain't real cheap, but beats doing the head!

Peter

I found out about Evans on this site. Goto: Evanscooling.com.

P E H

A no pressure system may solve a leaking water pump problem and that in itself would pay for the cost of the Evans waterless anti freeze. I plan to eventually convert all my engines to the Evans system.

P E H

HI. Is it possible the old radiator cap was not sealing correctly until the first time you experienced the condition which meant that the system was not working correctly until it started holding pressure?...Given the responses posted to your inquirery it's just a thought.


Brian

This thread made me curious. Just went outside to check my 87 300D. The car runs great in all respects. After 4 hours of cooldown there is zero pressure in cooling system. I suspect, as others have said, that this is the norm.

Cracked Heads :(
 

Dave M.,

Thanks for pointing me to this thread. Some how I missed it in my search for coolant leaks. As you say, the verdict is still out.

If I understand the theory of the cracked head keeping the system pressurized, the cylinder with the crack would need to be compressed at shutdown to force gas into the cooling system and keep it pressurized above the cold state that it started on.

You also mentioned that building pressure fast is suspicious. How long should it take to fully pressurize the system?

Nope, a cracked head will allow the 1500 psi combustion gasses to leak out into the cooling system any time the engine is running. Usually not enough pressure to force the coolant back in (a good thing, as the rods will all be bent if you try to start an engine with water in it!)

Evey compression/firing stroke will drive gas into the cooling system, the amount depending on the size of the crack or leak in the head gasket. Some cracks work the other way, slowly sucking coolant into the combustion chambers -- coolant dissapears without a detectable leak.

The cooling system should be almost completely de-pressurized until it get to operating temperature, and even then won't get to full pressure unless you have a large heat load, as in driving in traffic with the AC on. If you get substantial pressure below operating temp of within a few minutes this time of year, you have a combustion leak into the cooling system.

Peter

Evans WaterlessCooling System?
 

Has anyone used the Evans Waterless Cooling System in their Diesel or Turbodiesel? If so, I would sure like to hear about it - cost, benifits, ease of installation, etc.

Uh oh!
 

Peter,

That doesn't sound good. I have to check again to make sure, but I believe that one of the times that I went to add coolant I thought that the car was basically cold, but wham, I got hit with full pressure. :(

Typical problem with these cars. Usually only a head gasket unless it has been overheated. Mine is using more coolant than I would like, and I have oil in the coolant tank, too. No trouble, even on my trip to Florida, but I still believe I have a head gasket in my near future!

The original head was trouble. The re-design replacement is much better, but not cheap.

Peter

About the Evans coolant stuff - has anyone put that in a Mercedes OM617 or OM60x engine? It sounds fantastic at first, but after reading the fine print on their site I have serious doubts. Water pump modifications? Capacity increase required (to 3-4 gallons)? Possible flow issues? It sounds like they cater to American V-8's, I don't know if they even have a clue about Mercedes diesels. But if it is a drop-in replacement, I'm sure interested!

:-)

Craked Head!
 

I guess I'll be weighing in on the "cold pressure in coolant system means bad things" side of this discussion. Read on for further info.

Well things aren't going so well. I went to the parking garage without calling first so that I could see the car cold. First thing was the large amount of coolant under the car. Next was the pressure in the coolant system. Then I released it an confirmed that the pressure builds up promptly upon starting the car. No rough gurgling under acceleration, but quick pressure build up.

So I decided immediately to take it to my mechanic, Nick. They carefully washed the entire engine and inspected it for all the leaks. When the belly pan came off we had all three fluid types in great quantities: engine oil, ATF, and coolant. :( This was a dramatic change from 2500mi ago when I had the pan off to change oil and had small quantities of ATF and oil.

Now for the bad news. The coolant comes out of the head at a place above the head casket on the rear cylinder (I saw the fresh coolant on the clean head too). Nick says that in his experience this nearly always proves to be a cracked head. The oil leak at the casket and front seal is pretty heavy too. And the transmission seal leak is too bad to ignore any longer. I also have a rear bearing that needs replacing.

My wife and I have decided that we like the car well enough to continue to invest in it.

I'd appreciate any opinions on the following prices. Also anything I should be sure to do while I have the head off?

Labor to remove and replace head and front seal: $1300.
Labor to replace the transmission seal & rear wheel bearing: $500

Nick recommends a new head only. Nick gets his for $1850.

Thanks,

Hi Mike,

Wow - bummer! Sorry to hear the diagnosis. Yours appears to be in advanced stage of illness, relative to mine. Anyway, I recently called the dealer and was told the front main seal is ~3 hours labor, including removing the radiator. I was told (by a friend) the head gasket is 6-8 hours if done by someone with a clue, otherwise I guess it could be more like 10. My dealer's labor rate for "B" labor is $106/hr. So the labor you quote sounds a tad high, but not ridiculous. (Anyone else care to comment?)

I don't know about the tranny stuff, but if it's the front pump seal, the tranny needs to come out. You may want to replace the pump itself, I've heard that a new seal on the old pump doesn't work well because the shaft wears or something, the proper fix is a new pump (and seal). The pump would tack on another few hundred $$$.


As to what else to change while the head is off, unless they've been done in the last ~5 years or ~50kmi:

1- Injection pump vacuum shutoff valve ($20-30)
2- All 6 glow plugs (~$75-100)
3- Closely inspect the serpentine belt tensioner ass'y ($25-250)
4- Have all 12 valve lifters inspected for wear (~$20 each)
5- Have the timing chain inspected for wear/stretch ($???)


The BenzBin lists the head for $1495, the trans pump for $265, valve lifters for $16/ea, and the timing chain for $62. Rusty will usually at least meet their price, if not beat it - and his service is reportedly superior to BB.

MegaParts has the transmission pump for $235, but their prices were higher on the other stuff.


Good luck, and keep us posted!


Dave M.
Sacramento, CA
1987 300D - 229kmi
1987 300D - 234kmi
1984 300D - 206kmi

Mike:

Sadly, I suspect you mechanic is correct. At the very least, the head needs to be checked carefully. If it has not been replaced, the new head is much more resistant to both warping and cracking.

The coolant and oil leaks are typical of a failed head gasket, too, though, so you may in fact not have a cracked head. It is, though, probably cheaper to replace it than it is to have the work done twice!

The other prices are pretty much what I would expect. The rear wheel bearing is a pain -- seem to remember about $400 to change the one on my TE (previous owner's records).

Peter

Msyoder,

Does the new head come with the valves installed?

The labor cost is very high, sounds like about $100+ per hour. There is no mechanic in the world worth that much an hour to me. Of couse I would do it myself. Where else could I make $100+ per hour tax free? You could too.

I wouldn't replace any glow plugs unless the old ones were bad or the vacuum shut valve. There parts rarely go bad and if they do, they don't prevent the car from running or do any damage. If the cam timing is 3 degrees or more late, then a new timing chain is should be installed and maybe new chain guides..

P E H

GSXR
The only dynamic test that I can suggest to solve your dilemma is to leave sack of tomatoes(Sacramento)and head up 80 to Tahoe.If you have a blown headgasket or cracked head your temp gage will rise toward the red because of the exhaust gasses in the cooling system.
Good luck,
Peter

PEH,

Remember - this is an OM603 engine, not an OM617. TOTALLY different animals!There is a specific reason I said to replace the glow plugs and vac shutoff valve. Both jobs are a NIGHTMARE with the intake manifold in place. It takes 5 minutes to R&R the shutoff valve with the manifold off, and 1.5-2.0 hours with it on - BT, DT. Ditto for the glow plugs - they're nearly impossible to access. With the head removed, it is incredibly simple to replace these parts. If they have 5-10 years, or 100k+ miles on them, it's simple preventive maintenance that's well worth the extra $100 part cost, which is negligible considering the job would be $3000 without doing those two things, or ~$3100-$3200 with (assuming a new head is needed.) There's no way I'd leave the old stuff in unless recently replaced! The intake manifold R&R is also several hours (with cleaing it up, etc).

I agree on the timing chain, if stretch is less than 2-3 degress it's probably OK. Changing it as preventive maintenance is a judgment (or budget) call.

The heads come totally bare, except for seats & guides I think. No valves or lifters. The lifters are common failure also, they collapse and "tick". Again, it's easier to have these replaced with everything apart, yanking the camshaft to do them later is not fun...


Best regards,

Cracked Head :(
 

Nick says that the heads come bare (no valves or lifters).

I have already done the glow plugs, serp belt tensioner, and fuel pump shut off.

Luckily when a glow plugs started going bad they started with ones that I could change. Can't remember how many I was able to do without taking off the intake manifold, but IMHO it is impossible to do them all. I got the rest done when the manifold came off to do the fuel pump shut off.

I'm going for it -- i.e. I'm in for the head removal labor to see if it's cracked. May know by end of day or tomorrow.

Thanks,

Now ya'll have got me wondering about my 300D. It is strange. The car runs/drives/starts up great, no problems whatsoever but sometimes when I drive it and let it sit for a day or so I still have pressure in the coolant reservoir which results in a slight leak at the seal for the aux water pump (I am figuring because of the elevated pressure). I am not seeing any oil in the coolant nor white smoke. I do see the slight loss of coolant because of the aux pump. Once the 240D is up and running I may pull the head just for the heck of it to see if there is anything obvious. My narrow minded way of thinking would lead me to believe that if there were a problem then the "pressurized" coolant would eventually wind up in a cylinder somewhere which would cause a whole different type of problem (bent parts). Today when I got home I opened the reservoir cap and relieved the pressure which seemed to be comparable to the amount of pressure that is there after a day or so of cooling off. Funny thing is, during this time, the radiator was hot but the water temperature in the reservoir was not even warm. Also, when I opened the cap the level in the reservoir did not move.

It's normal behavior, but I dropped out of the thread because there's no way to prove it to someone used to the American/Japanese coolant systems.

Granted, a real crack can leak combustion gases into the coolant system. If that happens you'll start to see a negative effect on the running temperature.

I'd hate to see someone have a complete head job or even replace their head gasket when their car is behaving normally. If its not overheating, losing coolant, or showing any bubbles in the coolant, drive.

:)

Ken300D

Ah, Ken, Ken, Ken. I'm not as stupid as you (and others) may think! ;) It is not normal if there is HIGH pressure in the system when cold. A little pressure is no big deal, and could even be called normal. 15+ psi is way wrong when cold, period. I don't know why you think American/Japanese cooling systems aubmit to different laws of physics than German (European?) cars do. Try the simple squeeze test on the upper radiator hose with the engine cold. If it can be "twanged" like a guitar string that's not right. It should be soft & squishy. The cars never did this before, so do you mean to imply that zero pressure when cold indicated a *problem* with my cars, when they were running perfectly?

I don't think "engatawork" necessarily has a problem, though - it depends on the amount of pressure being described. I say that because he has an OM617, which are MUCH less prone to this type of failure. The OM603's have a known issue with head gaskets and cracking, 617's don't. I do think it's odd that the liquid in the tank was cool with a hot engine, sounds like possible flow issues? Thermostat? The level not changing doesn't surprise me, it usually won't unless the coolant is quite hot. But, as you say, if there is no coolant loss or overheating it might not be worth investigating.

Remember: Both of my 1987 OM603-engined 300D's, with high pressure when cold, ARE LOSING COOLANT!! Quite rapidly, too - a quart per 400-800 miles.


Regards,

Jim:

Sounds like your aux circ pump is dying -- it shouldn't leak even at 20 psi hot. A little residual pressure is normal, and a small leak will make it works -- air will get drawn in at the small leak rather than via the radiator cap.

I'm suddenly loosing coolant in the Volvo, which leads to poor milage and drivability problems when the cold start device stays on (no injection timing increase with engine speed). I smelled hot coolant last night, so I think it is time for all now hoses and a change to fresh coolant, along with new glowplugs and a check on the d.....d glow plug relay -- I think the glowplugs aren't heating proplerly.

Dave:

Mysterious coolant loss, especially if accompanied by high coolant pressure cold or oil in the coolant tank is a sign of cracked head or blown head gasket. A blown head gasket will eventually allow enough coolant loss to overheat the head, at which point it will crack. Best to replace gasket before more damage occurs, especially hydrolock!

Mike:

And anyone else faced with a cutoff servo replacement on a 603 -- pull windshield washer reservior, take two Cresent wrenches, and take off the ALDA (hex flats on ALDA and captive nut) -- it tips over toward the engine and rotates out from under manifold. This will give you enough clearance to remove the servo. Total job was less than two hours, next time will be on the order of 30 min. Much faster than removing the intake manifold.

Get a flex socket for the glowplugs, they can also be removed without removing the intake manifold.

Peter

Peter,

So far I haven't had any hint of hydrolock, or other obvious signs of coolant entering the combustion chambers. (knock on wood!) But I agree that I need to get this looked at no later than early spring, when it gets hot here in Sacratomato and the cooling system must be at 100%.

Now, about the ALDA - I've always wondered how hard it is to R&R. What does it connect to inside the I/P? If I wanted to "tweak" it to enrich the mixture a little, I could remove it, turn the screw, and then re-install? It would be nearly impossible to turn the setscrew & locknutwith the ALDA and intake manifold in place!


About the glow plugs, I know then can be done with the manifold and injecotr lines in place, but it sure looks like a multi-hour bugger of a job. Thankfully MB designed an oil leak at the #2 intake runner that develops over many thousands of miles, so when glow plugs are needed often the intake gasket is too. What a convenient coincidence! :) I'll be doing this on my b-i-l's 1987 300D sometime this month, as a matter of fact... already have the gasket, plugs, and vac servo from Rusty (Atlanta Wholesale Parts, 800-741-5252.)



Thanks again,

If your engine starts easily, you are wasting your time and money replacing yout GP. GP are not like spark plugs, after the engine starts they are shut off and have no effect on the operating of the engine. Since you might have to take the head off later, I would not bother replacing the gasket now. You might end up doing it again if you have to replace the head.

P E H

PEH,

I'm not sure I understand what part of my post you don't agree with. I said that if the GP's were recently replaced, leave them alone. If they are old, they should be replaced while the head is off, because otherwise they WILL FAIL eventually and the labor will be 5x as much after the head gasket job is done. An extra $75 in parts on a $3k job as preventive maintenance. Are you saying someone should leave old (or unknown age) GP's in just because?

msyoder's case is different, he just replaced the GP's and doesn't need to while the head is off. My one 300D had them done just before I bought it. My other one will get 6 new ones (IF I pull the head or intake manifold) because I have no records of them being done in the last 8 years and 100kmi.


BTW- do you currently, or have you ever, owned an MB with an OM603 engine? Or worked on one? I can't imagine you saying this would be a waste of time or money if you have...


Regards,

Dave:

The ALDA just sit on top of the actuator in the IP. Held on by a captive nut. Best to use a pair of small adjustable wrenches to get it off if you don't have some "shorty" wrenches -- space is tight (duh, I don't need to tell YOU this!). You will need to remove the windshield washer reservior for access.

My mechanic says he has never had to adjust the ALDA on a 603 -- if you don't get a little smoke at full throttle, check the overboost protection switch and boost lines before digging into the ALDA -- a clog or open overboost switch will reduce power quite a bit. Old tired hoses will give the same result, as will a plugged trap oxidizer, if you still have one, or a tired turbo. To adjust it, you will have to take it off.

The glowplugs can be removed using a deep swivel socket -- the kind where the socket is one side of the swivel. You will need one for the wire nuts and one for the plugs. Use a bit of paper to hold the nut in the socket when you put them back on.

I plan to do the head gasket on mine when the weather warms up, after I check to make sure I don't have a coolant leak. I replaced the thermostat this fall due to low engine temp, and will need to check for leaks there before yanking the head. The only symptom I have of a bad gasket is a slow coolant loss.

Peter

GSXR,

I'm not sure what a OM603 engine is. Is that the engine in a '87300SDL? I got one about a year ago but haven't worked on it yet because I haven't used it much.

However I would not change any of the GP just because they were old or I no records on them. When and if they go bad I will replace them. I always carry a spare GP like I used to carry a spare spark plug when I drove gasoline powered cars.

Even if a GP goes bad, it isn't a show stopper. One cylinder will just miss-fire for a short time after starting and then the engine will run normal until it is started cold again. The bad GP can then be changed at my leisure.

P E H

PEH,

Yes, the OM603.96x is the 3.0L turbo engine used in 86-87 300SDL's and 87 300D's. You are correct about the GP operation not causing anything really bad when one fails, other than a very rough running engine for the first minute of a cold start and a cloud of smoke too.

The whole reason I mentioned it is simply because of the difficulty of replacing them one at a time, only when they fail. On this engine, they are simply awful to replace. It's not like the older (through '85) diesels, where you have pretty decent access to them.

Regardless of engine, though, I believe they should be replaced as complete sets (except perhaps for freak short-term failures) - and more so on the 603 due to the increased labor time. If the plugs are original, or very old, and one fails - it's a bear of a job, and you'll probably end up doing the other 5 one at a time over the next few months or year or whatever. Why do an unpleasant job 6 times? My philosophy is that if one old one of a set fails, change them all - that way you do one unpleasant job one time. And, then you shouldn't have to worry about them for a LONG time, possibly the rest of the time you own the car! :)


Regards,