1987 300D is running too hot! Where do I look first?
 

I did a forum search and was overwhelmed by the amount of info. Where do I begin? Sorry, bit of a newbie here...

My car normally runs at 85-90 degrees all the time. The other day I'm sitting in traffic on a hot day, and my temp is climbing to like 110-115 degrees. I get home and open the hood with the engine still running, and I see that neither of the fans are spinning. The temperature goes back down if I can get up to speed, but when sitting in traffic, it quickly goes back up.

What is the first thing to suspect? Is it the thermostat that controls the fan? Or is it something in the fan clutch that activates it at the right temperature? The fan should be spinning if the temp is that hot, right?

I do have a greasecar kit installed, but that has been in place for months now, so I don't that is related to the problem.

Where do I begin troubleshooting?

Thanks!

in your coolant resevor. then check your thermastat

Kinda hard to diagnose but I'd start with the clutch fan. The next time the gauge reads over 110*C, pop the hood and stop the engine using the stop lever on the IP. The clutch fan should stop within a blade or two. If several blades pass or it freewheels, you've found a culprit if not the culprit.

Do a search on the 3-pin thermo switch on the upper radiator hose fitting. It looks like a thermostat housing but that ain't where the thermostat is in your engine. Anyway, I think that's the switch that tells the auxiliary fan to turn on a 115*C or some such setpoint. Do a search to confirm which thermoswitch controls the fan. You can ground one of those pins to test the fan.

If this occured with the AC running then do a search on which of the receiver/dryer pressure switches triggers the fan.

Sixto
93 300SD

If you want a temporary fix until you figure out the root cause, you can jump the two terminals for the aux fan at the temp sensor with a short piece of wire and it will keep the car cool, even if the radiator fan isn't working. That's assuming that your aux fan isn't shot. Also check the two fuses for the aux fan, they may be shot too.

In addition to the clutch fan, many of these old vehicles have issues with airflow through the radiator and condenser.

My SD has now taken on a dose of the "100's". Even in 50 degree weather, it can creep up toward 100C. in low airflow conditions.

The clutch fan is working correctly so, I'm quite sure that the passages through the condenser and the radiator are partially clogged with dust and debris. If you take a look at the front of the condenser, you'll find it unbelievable that any airflow whatsoever gets through to the radiator.

So, to remedy this situation, you'll need to remove the radiator from the vehicle and thoroughly clean the fins with condenser cleaner and compressed air or a low powered pressure washer. It's a long tedius job to get all the debris removed. But, hold the radiator up to the sun and peer through it. You'll see the task at hand.

The condenser needs a similar treatment, however, it's more difficult because you can't remove it from the vehicle. I have not done the compressor, personally, but, I'm fairly sure that it's due for the same treatment.

With restricted airflow through the radiator, will the fan clutch get hot enough to engage?

Sixto
93 300SD

The entire situation with the fan clutch leaves me with questions.

Dave has stated that the clutch won't "engage" until it sees 100C. But, if this were true, a brand new clutch and radiator would allow the engine temp to climb to well over 100C. until the clutch "engaged".

Personally, I don't believe that it "engages" similar to a step function at a given temperature. It probably happens more gradually, beginning at a temp. of 85C. and finishing (fully coupled) at a temp. of 110C. These figures are just a guess.

With restricted airflow, the temperature at the fan would likely be hotter than with full airflow. The reduced quantity and velocity of the air will be warmed to a higher temperature and thereby cause the fan to engage sooner. This would be a desirable result of a partially clogged radiator.

The fan clutch is a problematic issue to me:
The older fan clutch with aluminum fan in my car (300D 87) was bad. It would allow temp to be close to 105 and then the electric fan kicks in.That is when the car is not moving, once the car moves temp drops to 90-95. The older fan clutch was described as "stepless" in MRBZ cd and may be the newer ones also? which means no gradual engagement??
I replaced the fan clutch with the new style (sachs with a plastic fan @ $250). That was 3 - 4 years ago. The new fan clutch was doing its job very well. It keeps the car between 90-95 all the time. about a year ago, I started to notice the sound of the fan coming more frequently. I thought it is because engine gets hotter. But later I tested the fan clutch and found that its de-coupling mechanism is not working properly. It stays engaged strongly even when it is not needed. I read many posts here and many said that it suppose to be like that (which seems to be wrong to me). Then I read the article in the do-it yourself part in this forum about replacing fan clutch in newer 606 engines. It says that the older fan clutch can be defective due to a failed coupling mechanism which results in excessive fan engagement. In the post, the defective fan clutch is similar to my newer one (sachs) which indicated to me that many of these sachs units can be defective as mine or can fail sooner in this way. The newer one is made by "vemo germany". I am planing to replace mine sooner. The good news is the newer fan clutch "vemo" is only $90!! but you need to have the plastic fan, the old aluminum fan will not fit. I think MRBZ revised the pricing of fan clutchs and lowered them as they are important maintenance items and were price rediculously high. Also, in the older versions, the ones for diesel are diffirent from the gas engines ones. So, my advice to you:
replace the fan with a pastic one, CONFIRM that the newer fan clutch (I think for 606 or later engines) fits in your engine (603) install it and you will be happy.
The other thing is you need to make sure the electric fan will kick in by testing the switches - it should not come in usual situations when the fan clutch works. And you need to check the thermostat (it usually fails open, but still restrictive. If the car takes long time to warm or the temp drops below 90 while cruising, then thermostat is failed). All this will keep the car in good shape unless your radiator is VERY bad, needs flushing, restricted etc., then you need a new one for extra cool engine.

What exactly is the difference between a 300E and 300D (or 300SDL) fan clutch? I have heard of people using the gasser clutch on a diesel, in fact I think that's what I just ordered for mine.

LOTS of crap will come out of the condensor, I hosed mine out on the SD here when going through the AC. Made me want to puke. Tons of bugs, rocks, dirt, etc.

Remove the rad (consider to replace too) and take it to a shop to have boiled out. Then flush the system properly. Green coolant = bad.

I figure the SDL tax. Same one I sent you is on my car...

The best aux fan switch is the RED one. 100°C/110°C (fan on high/compressor off). They're maybe a $20 and never work anymore.

As I inspected the fan a bit closer, I realized that the tips of the fan blades that are closest to the radiator were all clipped off, apparently from abrasion on something. The radiator fins also seemed to be chewed up in a circular pattern; though oddly enough, not matching the location of the chipped fan blades. When I moved the fan manually, it broke free of some obstruction and broke off a chunk of one of the blades. Maybe the blade was already cracked, and I just broke off the already cracked piece. It's really hard to see in there, so I'm not sure where the blades were rubbing. Anyway, it spins free of obstruction when I turn it manually now.

What's up with that?! The fan doesn't move front to back when it engages does it? Why would it be all mangled, and the radiator mangled, but yet it spins free of obstructions?

I'm stumped. :confused:

The aluminum fans have a notch in each blade. An aluminum fan will chew through a radiator and have little wear to show for it.

Is the shroud not sitting properly around the fan? There's nothing close to the circumference of the fan that wouldn't suffer the brunt of contact.

Sixto
93 300SD

I have a plastic fan, and the radiator looks newish, as if replaced by the PO. There is one part of the plastic fan shroud that is close to the blades - I'll have to find some way to pull it out of the way...

Where did the coolant go???
 

I stumbled upon this thread the other day and I have been following it as I have just started to have a problem with similiar initial symptoms. It's not my intention to hi-jack the thread, but I figure if I can get some help without starting a new thread, all the better.

I have an '81 300 SD. When the car is moving the temperature is just above 80*. When I come to a stop, the temp was climbing to 110*. As soon as I started moving again it would drop back to around 80*

When the temp. got hight I jumped out to see if the small fan in front of the radiator (auxiliary fan?) was spinning. It wasn't..

When I got home I popped the hood, and to my surprise, the coolant reservoir was empty. When I first got this car a few months ago I checked all the fluids every other day as a precaution. I learned then that I could not keep the coolant level at the fill line on the reservoir because it would be pushed out of the overflow hose that is by the cap. The coolant would level out about an inch below the full line, or so I thought. Other than some drops of coolant exitiing the overflow hose, I cannot find any coolant leaks.

Where could the coolant be going?

Other than being rought at initial start up, the car runs like a champ.

Anyway, I refilled the coolant reservoir. Now I am not getting the car above the 80* mark. The small fan is still not turning on, but is it suppossed to at this temperature?

I saw the post by Sixto about the 3 pin thremo switch. I did a search for this and came up empty. I'm not sure if it even applies to my car, as I follow the wires from the fan, to an inline plug/connector and then into the bottom of the fuse box. I have no idea where they go at that point. I checked all of my fuses, and they test good. I don't know how to test the releys that are in the box.

Other than keeping a closer eye on the coolant level, can anyone offer any suggestions?

I would like to know where the coolant is going and I would like to figure out if my fan is good or not.

Thank you.

What model/year?
 

You don't include any info about the model or year, please fill us in.

On my 87 300D I get a low coolant level warning light before the resevoir gets empty. Mine is leaking around/at the aux coolant pump. Right now I am feeding it and watching it.

And looking for another aux coolant pump. Anyone have a spare????

-Jim

1981 300 Sd

For my '87 300D, can anyone tell me where to find the main thermostat, and also the switch/thermostat that controls the smaller fan? What do they look like? Where are they located specifically? My small fan also does not come on even at 110 degrees. Just found out that I have the #14 head, so I'm extra paranoid about heat issues! :eek:

Thanks!

Others will be able to help you more than me, but here is a short list:
Check your oil. Make sure that it is black and not creamy/emulisfied. (If you just changed the oil it will be black in a couple of blocks. :) ) Creamy emulisified oil means there is water/coolant in your oil. That is bad.

Park in a clean spot or put some card board under your car. This will at least give you a hint on where to start looking.

Umm, that is about all I can think of. Good luck with that!

-Jim

Usually the coolant is leaking somewhere. I'd first advise a pressure test of the system and search for any leaks.

If you are sure that you have no leaks, then the coolant is disappearing into the oil via a bad head gasket or a cracked head. An oil analysis will confirm this. Don't delay in diagnosing this issue. Coolant is not healthy for bearings and camshafts if it accumulated to any significant amount. I had the same issue on my SD. Had a cracked head that needed replacement.

Thanks, guys,
The oil looks fine, on the dip stick anyway. The only coolant leak I have ever found on this car is what comes out of the over flow hose by the the reservoir cap.

Is a Blackstone oil analysis the only way to derermine if there is coolant getting into the oil?

Any tips on trouble shooting the aux. fan on this '81 300 SD so I can determine if it's doing what it should?

Forget the look of the oil. If you wait until the oil turns milky white, you've waited far too long.

Blackstone or the Mobil analysis that I use are fine for checking whether Glycol is positive in the oil.

Disconnect the fan at the plug and apply 12V and ground to the plug. See if the fan is working. Many times they are toast. I'm replacing the fan on the SD as we speak.

Stupid questions?
 

Maybe dumb questions, but if I'm losing that much coolant into the crankcase oil, wouldn't I see the oil level go up, or at least stay steady, rather than having to add a quart every few hundred miles?

Regarding the fan, does it matter which side of the plug I apply the 12 volts to?

The coolant boils off almost instantly, unless you're really leaking a serious amount and it gets emulsified. But, you won't see any increase in oil level if you're drinking a quart every 1000 miles or so.

Only if you care which direction it turns............;)

Replace the t-stat if it's not recent - use OE/OEM only (Behr, Wahler). It's located where the lower radiator hose connects to the engine. Unscrew the round sensor with one wire attached directly in front of the housing, this will make it MUCH easier to R&R the t-stat. (Trust me.)

About the overheating, assuming the t-stat is good, rad cap is good, there's no leaks and the system holds pressure, and the radiator & condenser fins are clean... you either have a bad fan clutch, internally corroded radiator, or both. The clutch is more likely especially if it's original. You can refill it with silicone if the bearing is good (search for details).

The electric fan should trigger at 105°C... it's controlled by the 3-prong switch shown in the photo below. With the engine running, unplug the 2-pole connector and short the two female sockets together... the fan should turn on. If so, replace the switch. If it doesn't, figure out why (and I'd still replace the switch on principle... I've yet to see one that still works after 15 years.)

http://www.w124performance.com/image...ch_105-12x.jpg

Thanx, GSXR
 

The lower radiator hose is looking like it's in need of replacement, so that will be a good time to do the thremostat also. Thanks for cluing me in on the location of the t-stat. I thought it was at the upper hose.

Since topping off the coolant, it hasn't gotten much above 80*, but I do plan to investigate the fan further. On my '81 300 SD, where is the 3 prong switch that you show the picture of located? In re-reading this thread, I think it's by the upper hose, where I originally thought the t-stat was. Am I correct? Is accessing it and changing it out as straight forward as one would imagine?

Before I do much, I want to further investigate where the coolant is going. With my next oil change, I plan to send a sample for analysis to see if it's a cracked head. I know the system is holding good pressure, as even after the car has sat overnight the radiator cap comes off with a "POP."

I find it odd that whenever I look at the bottom of the overflow hose, there is fresh coolant dripping out. Only a drop or two when I look, but it is visibly moist with coolant. As an experiment, I have just place that overflow hose into a plastic bottle in an effort to see how much is collected over the course of a few days.

Sorry, firemediceric, the info in my post is for the 1987 300D (original post topic), not your 1981 300SD. That 3-prong switch doesn't exist on your car, AFAIK. And, I think on your engine, the thermostat is at the upper radiator hose, not the lower. The 124/603 and 126/617 are TOTALLY different systems.

:(

The radiator cap should not come off with a 'pop' when the engine is cold. In fact there should be zero water pressure. You could have a crack or head gasket allowing combution gasses to enter the cooling system. Cracks or failing gaskets do not always result in oil and coolant mixing.

Dave, you rock! Thanks for the picture and description of location. Yes, I'm pretty sure I need to replace that switch.

gsxr,
Thank you for the clarification. I was looking at the wiring for the fan and it seems to run straight into the fuse box with only an in-line plug between the fan and fuse box, so I'm not sure how to see if the fan is getting the signal it needs at the proper time/temp.

rrgrassi,
given the car's symptoms, how do you suggest I proceed? Especially if a UMO analysis may not show coolant in the oil even if the head is cracked? The car, after it warms up, runs great. I hate to go looking for problems.

Do the oil analysis, as instructed, because even if there is no mixing, vapors do condense and can leave a tell tale residue the anaylsis can pick up. It possible to have mixing, but not enough to give the oil a "milk shake" look to it, like Brian Carlton said. Also do a compression and leak down test on the cylinders. You can also check for bubbles coming in to the coolant tank, with the cap off, and engine running. Take the cap off while cold, start the engine and let it idle until it reaches it's normal operating temp. Look for bubbles while the car warms up. When the engine is cold, it is possible for the cracks to seal due to the contraction of the metal, and then open a bit as the heat causes the metal to expand. I had a gasser Datsun F-10 do that. Started running hot, and losing coolant. The radiator showed bubbles when the engine ran. The Datsun also had some water on the #3 piston. Turned out to be a head gasket, and that was only seen after disassembly. Also repaired a Ford 460 that blew a head gasket. Only way to tell on this one was the water drooling out between the head and the block on the front of the engine. No visible oil/water mixing in either case. So do all the testing you can before throwing money at repairs.

Well, I guess I'll be scheduling with my mechanic to have him do the compression and leak down test.

It may not be related at all, but my oil pressure is pegged to the top when I'm driving. I guess that doesn't indicate that the engine is healthy and has good compression?

It's really puzzling, as the car runs fantastic, once it warms up.

I wish I had a good mechanic that knew these cars, but no one has been recommended to me in this area

A compression & leakdown test likely won't show much of anything. The oil pressure should be pegged anywhere above idle, that's normal, but only indicates that the main bearings are not worn. If you are continually losing coolant internally, my first guess is a head gasket, as the 617 isn't known for cracked heads. If it was a one-time problem, forget it. I assume you have a new or recent radiator cap?

BTW, the electric fan on the W126 (and W123, 124, 201, etc) does very little for engine cooling, it is there almost exclusively for the A/C system (to provide extra airflow at idle, when the main fan isn't doing a whole lot at low RPM). The main mechanical fan provides 90%+ of engine cooling. For some years/models, the electric fan will NEVER turn on based on engine temperature (for example, the 82-85 300D), only based on a signal from the A/C system.

You should probably start a new thread under the topic 1981 300SD, since your problems are in no way related to the 1987 300D...

:wacko:

Different opinions
 

Thank you all for the input. All of you are a lot more knowledgeable than myself in this area, yet there seems to be some difference of opinion as to the best way to diagnose the problem.

I think I will definitly send the oil off for analysis, but not rush right out to drain the fresh oil to do so.

I will take rrgrassi's suggestion of looking for bubbles in the reservoir as the engine comes up to temp.

Some feel that a compression and leak down test will tell the tale, others are not so sure. I will ask my mechanic (who is great on my F-350, but has little experience on these old MBs) his opinion, but once again I may not call him today, as I want to see how much coolant is forced out of the reservoir, through the overflow hose and into the little catch bottle I made.

I may pick up a new radiator cap some time this week, just to rule it out. If the cap were the problem, wouldn't I see moisture on the reservoir around the cap? Also, wouldn't the cap not hold pressure?

I'm glad gsxr straightened me out on the aux. fan, before I pursued that further with wrong expectations in mind.

I had hoped to avoid starting a new thread and cluttering up the forum, as I thought I had a simple issue that I was just too ignorant to recognize.

The cap holds pressures to 18psi IIRC, Mine is by JOST and I do know what it's rating is. If the pressure exceeds what the cap will hold, then the spring will be forced open and excess coolant or pressure should be vented via the vent tube that is attached to the filler neck of the resivoir tank. You might not see coolant on top of the tank it self, and since it is in a wet environment, you will more likely yhan not see coolant around the cap seal and filler neck.

rrgrassi,
You educating me on something so simple may have just solved the problem.

If I am understanding you correctly, a bad/worn out radiator cap would allow the coolant to exit the overflow hose, as I am seeing idications of. Am I correct?

Why would I be feeling and hearing the slight "POP" when removing the cap, even when the car has sat overnight, if the cap is bad and not holding the pressure it should?

Glad I can help. I get so much info from this forum, it's good to able to give back.

Yes, you are correct, but if pressure exceeds, then the cap is supposed to allow escaping, but I have seen scale and rust buildup on the cap that does not allow pressure to escape resulting in other part failures like W/P seals, etc, as the pressure cannot escape, except from the next weakest link.

The popping should not occur at cap removal, and if the pressure is below the cap's rating, it will not escape. Is the upper hose hard to squeeze cold like it is after a good hard run on the highway? The upper hose should be easy to squeeze when the engine is cold, and cap on the tank. If the hose is easy to squeeze, then odds are in favor of not having combustion gasses pressurizing your cooling system.

If pressure is there, you should get a hissing at the first indent at cap removal, and even more hissing, or nothing at the final indent, when you pull the cap off the tank, like when you remove it when hot. The first indent is designed as a pressure release so you do not spray hot coolant all over you.

Where does the pop originate? It just be the rubber seal flexing on cap removal, kind of like a cork on a wine bottle. No pressure, but still a pop.

Mixed results
 

rrgrassi,
I checked what you suggested and came back with what I think are mixed results.

The car has been sitting for the past 9 hours, so the engine is cold. The top radiator hose is soft and pliable. I can squeeze it easily. Good?:)

When I went to remove the radiator cap, it hissed and spurted some coolant, spraying it across the top of the reservoir. Bad?:(

Since some coolant has been seen dripping out of the over flow tube, and at the same time the cap is holding pressure, doesn't that mean the cap is good?

On a positive note, the coolant level did stay where it was in the reservoir on the 40 minute drive to work early this morning. I hadn't lost a drop to the catch bottle I set up at the end of the overflow tube or any where else, as near as I can tell. The car also never got much above 80*

Top hose soft and pliable cold is a good thing. That is how it should be. Your cap could be good, but if it is weak, then is is not letting the system pressurize normally. That is bad, as the pressure helps keep the coolant from boiling, which results in air pockets.

You can also get overflow like that if your tank is too full. No room for expansion will results in higher pressure, so the cap the acts as a pressure relief. It is possible to have a little pressure that can cause hissing and spraying of coolant when cold. That is also caused by the cap and the rubber seal holding onto some coolant that did not drain back into the tank, or the drain tube. If the drain tube is restricted, that can give the same results, but it is caused by a vacuum instead of pressure.

Try replacing the cap, and check your drain tube for a restriction. Keep an eye one the coolant level.

Problem solved!
 

I just noticed that I never did resolve this thread.

Boy do I feel like a dumb-ass! My fan blade was lodged against the radiator. As I tried to move it, a chunk of one of the plastic blades broke off, and the fan was freed. Now I wonder why my fan was in contact with the radiator all of a sudden, when it was spinning freely before?

The front radiator support on these cars bends inward VERY easily. If you tapped a curb with the front of the car when parking, this pushes the bottom of the radiator into the fan blade. With the metal fan blades, this destroys the radiator. To be fixed properly it really needs to go to a body shop to have the support pulled out. The lower engine shield also won't fit properly, as the holes won't line up anymore.

If this is what happened, you need to fix it ASAP. You can attempt a partial fix using a bottle jack against the support, braced against the sway bar, with a wood block between the sway bar and oil pan. But it won't fully correct it, and it's not the right way to fix it. I'd be surprised if this wasn't the cause... I've had this on both of my '87s.

:kid: