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Old 12-09-2002, 11:59 AM
jsmith's Avatar
Join Date: Aug 2001
Location: At Sea
Posts: 1,729
activation for the viscous fan clutch is at a very high temp. although they may go out, they typically are not at fault. you can do a search on viscous fan clutch or VFC to get more info on this. it's difficult to get a sense of how hot the radiator fins are because they are very efficient in dumping heat specially with wintertime ambient temps. the top of your radiator should at least be very hot to the touch. if you think the radiator is not cooling then either it is clogged or the thermostat is not functioning properly. there was a report that there is possibly a bad batch of thermostats out there. re: the water pump - it will start weeping coolant when it is shot so if you have no coolant on the floor it's probably ok.

BTW, "Mercedes" thermostats are either Wahler or Behr. the Wahler thermostat is stamped with the brand. the Behr has a "made in Germany" & "BTT" stamped on it...
1993 300e-2.8
- gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
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Old 12-15-2002, 02:25 AM
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Join Date: Dec 2000
Posts: 368
If it free wheels that much with the engine at operating temperature replace the clutch. I just had the same problem with a 94 C280. New clutch solved the problem.

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Old 12-15-2002, 12:28 PM
Posts: n/a
Do you HEAR the fan lock up when the temps rise, say around the 100' mark or higher? I can hear mine whirring starting at about 90' on up off idle. Very noticeable, you won't miss it unless the radio is cranked


95 E320
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Old 12-18-2002, 09:09 PM
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Join Date: Feb 2002
Location: Canton, MI
Posts: 54

1. I can not hear it "roaring" as I have heard described.

With the engine (99 deg C) I shut it off and watched the fan spin. Spun many times as I stated before, but this time I checked for play in the bearing. Seems there is about 1 mm movement in the fan clutch when push/pulling at the 3 and 9 o clock positions on the fan. Problem? I think so. Agree?

Could not get the temp any higher.

2. Pulled the sensor that controls the fan (two prong) and shorted the two terminals. Fan turned on fine. Read this in another thread.

3. The rad is warm all over after the car had been idling for a few minutes. Cool though after driving. I think Joe is correct, the rad was dumping the heat in the 20 deg F temps in MI. My bad.

4. Oh, the T-Stat is a Behr, and replaced two months ago.

5. I checked the cap on the tank after sitting overnight and it still had slight pressure that was released. This leads me to believe cap/tank is ok.

6. I did the water wetter. Figured for $8 maybe I will get a little less surface tension near the heads/combustion champber and get better cooling locally. Temps do seem to drop back to normal quicker after being stopped. Still go to 99 though.

I will keep at it and let everyone know when I do solve this puzzle.

Fan Clutch loose......problem?
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Old 12-18-2002, 10:40 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,509
I'll post the same response to your problem that I post to everyone who thinks their E320 is running hot at 90 degrees.

It's not. It's perfectly normal. It's the temperature the car was made to run at.

If you think about it, with an 87 degree thermostat, the temp that your t-stat starts to open is 87 degrees - not the temp that it is fully open, but the temp that it starts to open. I'm sure your car should be running between 87 and 95 degrees most of the time when running on the freeway, and will probably run about 100 degrees at an idle in hot weather. Here is what the CD says about the cooling system and temperatures on M104 engines:

Thermostat will start opening at 85 to 89
Thermostat will fully open at 102
Viscous fan clutch will cut-in at 96 to 104
Viscous fan safety cut-off will ocurr at engine rpm 4500
The same will ocurr at fan rpm 3250
Electronic fan (1st stage) will cut in at 16 bars of refrigerant pressure)
Electronic fan (1st stage) will cut out at 11 bars
Electronic fan (2nd stage) will cut-in at 107
Electronic fan (2nd stage) will cut-out at 100
A/C will go into 50%on, 50%off cycle (20 seconds interval) at coolant temp 121 to 123
A/C will go into emergency shut-off mode at 126 to 128
Pressure cap will open at bar 1.3 to 1.5
Coolant temp max is 130

Remember that water boils at 100 degrees celsius, but with a 50 / 50 mixture of water to coolant, your boiling point is raised to 120 degrees, and Mercedes designed this car so that it isn't considered to be overheating until the temp exceeds 130 degrees.

MB designed these cars to run hot, and 100 degrees is not even considered close to being hot. Your thermostat isn't even in the fully open position until 102 degrees. Further, the 2nd stage high speed fans comes on at about 107, and shuts off at 100! How can 100 be considered hot if that is the temp that the high speed fan shuts off at?

Now, many of us on this forum (including me) second guess and doubt the wisdom of the German engineers for these cars, and carry out modifications to prevent the car from going much over 100 degrees.

I have installed the "cool harness" that JimF sells, and it works by changing the electrical resistance. It fools the high speed auxillary fan to engage at 100 degrees, and it continues to run until the temp reaches 82 degrees when the fan shuts off.

I am using this "cool harness" as a crutch, I guess, but I don't think I really "need" it. My car is the same as yours, and mine runs between 92 and 95 degrees on the freeway. When I pull off the freeway, the car runs between 95 and 100 in city driving.

In any event, I am 100% completely convinced that your car is running at exactly the temp it was designed to.
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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Old 12-18-2002, 10:42 PM
Ken Downing
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When you look at cost... After checking the Belts and Thermostat the next thing would be to replace the fan clutch.. They are not much work and do not cost a lot..

Worst thing that could happen is you would have a spare..

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Old 12-18-2002, 11:19 PM
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Join Date: Aug 2002
Location: So Cal, Beach
Posts: 250
Welcome to the black hole...................
280SE 4.5
Sandals (size 11)
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Old 12-18-2002, 11:37 PM
Posts: n/a
Tim, you hit the nail on the head. I can't tell you how much money I've spent on my cooling system thinking there were problems. I did, however, have a bad fan clutch (after the engine was hot I could grab the fan at the 12:00 o'clock position and move it about and inch forward and aft. Definitely bad fan clutch!! But to get used to an engine running around 212'F is still more than I can handle. I recently installed a 82'C Thermostat and now it never goes above 90'C (it is fairly cool out too so I don't know about this summer) so at least I feel better. But I can gaurantee most people out there are chasing a ghost problem that really isn't a problem at all.

Having said that, I found a radiator shop that is going to build me a custom radiator (thicker and wider) for $350.00. Why you ask would I do such a thing, because I too am obsessed with keeping the engine as cool as possible (around 80 to 90) at ALL times, not just in the winter like what we're in right now......I sure wish Mercedes had just installed a temp. sensor with a null area in it like most all other manufacturers, then no one would really know how hot the engine is running until the aux. fans kick on.

Okay, I'm insane.........maybe I should just unhook the damn temp. gauge and forget about the whole thing...Just kidding....

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Old 12-19-2002, 12:57 AM
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Join Date: Aug 2002
Location: So Cal, Beach
Posts: 250
Dale, I think we just have a hard time thinking or beliving all this new sh#t, look at the cooling system on a 95 or so Honda car, the radiator is about the size of a poastage stamp, Go Figure?

Just like Stephen Stills said in the 60's " Somepthing's Happening Here"

Maybe us old guys need to take the "Black Pill"

280SE 4.5
Sandals (size 11)
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Old 12-19-2002, 01:13 AM
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Join Date: Jul 2002
Location: Middletown, DE
Posts: 739
I'm with suginami, my 190 D runs at about 95-99C on freeway. in winter with heat on I don't believe t-stat opens at all (so-cool rad). the main fan (hydromatic clutch) kicks in at 110C and shuts off at 100C. the aux fan starts only with ac on or temp at 115C.

The way I checked both fans- turn off the heater/clime control completely. drive hard for 1/2 hours (or less), stop and idle. in winter it may take about 15-20 minutes. finally, open the hood and look at the fan (kinda like watch grass grow). your main fan should kick in at 104C and should stop at 96 C. And you will know when it stops.

I did not like how slow the temp dropped, so I slaved the aux fan to the main. Now the temp drops in about 10 seconds. My advise (and I was KILLED for giving it on this forum), leave the car alone. As long as the temp does not exceed the one where the main fan should start at (104C ?), you should be OK.

BTW I replaced 85-95 t-stat with a 80-90C t-stat. The result - the running temp in summer did not change, but in winter the car is running too cold (80 C instead of 95C) and it takes a while to heat up. I'm going back to the original T-stat.
1985 190D 2.2l Sold-to Brother-in-law
1996 Mustang 3.8l -"thinks it's a sports car"
1988 Grand Wagoneer - Sold (good home)
1995 Grand Cherokee Ltd -"What was I thinking??!!"
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