1987 300D is running too hot! Where do I look first? - PeachParts Mercedes-Benz Forum

Diesel Dan · #1 10-07-2006, 01:26 AM

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!

midenginev8 · #2 10-07-2006, 01:31 AM

in your coolant resevor. then check your thermastat

sixto · #3 10-07-2006, 02:56 AM

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

Jmana · #4 10-07-2006, 10:56 AM

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.

Brian Carlton · #5 10-07-2006, 11:48 AM

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.

sixto · #6 10-07-2006, 02:07 PM

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

Sixto
93 300SD

Brian Carlton · #7 10-07-2006, 02:16 PM

Quote:

Originally Posted by sixto

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.

toknow · #8 10-07-2006, 02:59 PM

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.

Jmana · #9 10-07-2006, 06:42 PM

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.

Hit Man X · #10 10-07-2006, 07:40 PM

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.

Diesel Dan · #11 10-07-2006, 08:20 PM

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.

sixto · #12 10-07-2006, 08:25 PM

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

Diesel Dan · #13 10-08-2006, 11:36 AM

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...

firemediceric · #14 10-08-2006, 05:47 PM

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.

Jadavis · #15 10-08-2006, 06:23 PM

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