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Old 12-11-2001, 09:48 PM
Posts: n/a
Angry 190e overheats only when Idling for 20+ minutes

If anyone can answer this one you will be my Hero!!!!

car: 190e 2.6 1993
Problem: car overheats and/ or runs right beneath red temp line only when it idles for more than 20 minutes.

Recent work:
1.) replaced the water pump with an OEM graf water pump, changed hoses

2.) changed radiator fluid (60:40 anti-freeze to H20 mix),

3.)tried both the old Mercedes thermostat and a wahler thermostat.

There are no leaks in the system by visual inspection.

Operating temp when driving is just a touch above the 80 degree Celsius mark. No problems what so ever when the car is moving.


If I just let it Idle for more than about 20 minutes, it overheats or hits the white (120 degree Celsius) line (depends on the mood the car is in I guess). This occurs with the heater on, heater off or AC on. It seems like it warms up faster when the heater is on.

The Auxiliary fans kick on when the temp hits around 100 degrees Celsius, and does and adequate job cooling the radiator down (I can touch the radiator and it cools off when the aux fan kicks on).

If the temp gauge hits 120 degrees Celsius when Idling, I can rev up the rpms to 3000 and the temp drops to 90 degrees Celsius.

Please help!!!!

Some of my questions are as follows,
What else could be wrong?
How else can I test the cooling system?
It appears that the auxiliary fan is working appropriately.
I tried two different thermostats with the same result.
Could it be that the OEM (graf) water pump can not pump enough fluid when at Idle speed to keep the engine cool when idling?
How can I a mechanic look at this, and feel sure that I'm not getting screwed (e.g. what would be the normal number of hours billed to trouble shoot this).
Can anyone with a 190E (that is working well) tell me what happens to their temperature (e.g. what is the temperature range) if you let you car Idle for 20-30 minutes.

Again I'm desperate, and ready to blow up this car!!!!!


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Old 12-11-2001, 11:43 PM
dacia's Avatar
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Join Date: Mar 2000
Location: Here.
Posts: 315
Check the viscosus-coupling fan clutch. It is the big fan attached to the front of the engine between the rad and the engine. When you rev the engine it should change speed. If it does not there is your problem. It is about $200.00 give or take and easy to change. The fan blades can be removed from the clutch.
Good luck.

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Old 12-12-2001, 12:06 AM
Registered User
Join Date: Apr 2000
Posts: 412
Make sure the electric fans are pushing air thru the radiator towards the engine. My 190e 2.6 was running a bit hot. One of the fans was replaced and was wired backwards. It was pulling air from the engine compartment. A simple test would be to place a sheet of paper on the electric fan grille and see if it sticks to it,if it does its working right.
Also you should checkthe operation of the thermostat by boiling it in a pot of water and examine when it opens and if it stays open. I had a similar problem and was puzzled that the car would heat up rapidly in traffic but would run cool on the highway. I discovered by boiling the thermostat, that it was warped and would only open a crack thus poor circulation at idle. My cooling system now works perfectly.
Good luck.
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T
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Old 12-12-2001, 02:54 PM
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Wink Correction to the radiator fluid mixture

I apologize there was a typo
the radiator fluid mixture is 60% water and 40% antifreeze.

Thanks for the input. I will check and try the recomended evaluations and see what happens.

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Old 12-12-2001, 04:59 PM
Registered Diesel Burner
Join Date: Aug 2001
Location: Northern Virginia
Posts: 2,911
I don't have this particular car. But in general, when the engine compartment is warmed up with the engine off, you should NOT be able to spin the fan much more than 1/4 or 1/2 turn by hand. You know, grabbing it on a blade and giving it a spin.

If it spins for a couple turns you need a new fan clutch assembly.

Hope this helps.

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Old 12-12-2001, 05:14 PM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,232
I'm sitting here wondering if the thermostat is installed in the correct position. Was it running hot prior to the work? Is this the reason the work was performed? If the electric fans are operating correctly then the other item I would question is the condition of the radiator - sounds like you may be experiencing some pluggage. Also, make sure that block is filled with coolant/water too (no air in system).
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Old 12-12-2001, 11:41 PM
Registered Diesel Burner
Join Date: Aug 2001
Location: Northern Virginia
Posts: 2,911
Hi tkamiya

Let me explain the test a little clearer. I'm talking about how far the fan will go with one push.

Yes, of course if you keep pushing it again and again it will keep going around. But with one push it should not freewheel very far.

The fan clutch controls how tightly coupled the fan blade is to the engine shaft running it. Under cool conditions, the fan doesn't have to move much air - so to save engine horsepower the fan clutch slips a lot. However, under hotter conditions more air is needed, and the fan clutch tightens up to make the fan run harder.

Hope that explains it better!

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Old 12-13-2001, 03:53 AM
Neil Eglintine
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Aaron, I'm not afraid to ask the dumb question!

Are you sure your motor is overheating and it's not just your temp guage playing up? Or maybe you're just too anxious about it. You say you can touch the radiator while this is happening. This does not sound like an overheating motor to me.

My 190E will run up to about 110 when the fans kick in and it cools down. Been doing that since I bought it 50k ago and no overheating probs at all. I might worry if the guage went into the red on a regular basis but otherwise I stay cool, just like my motor
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Old 12-13-2001, 06:39 AM
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Join Date: Sep 2001
Location: Lathrup Village, Michigan
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My 190E will run 80-85 degrees.

Make sure that the aux circulation pump is working. It is mounted next to the exhaust manifold. It's purpose is to make sure that coolant is flowing at idle. Apparently, the water pump cannot flow enough at low rpms.
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
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Old 12-13-2001, 08:10 AM
Dave McDonald
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I have a 230CE on a '85 123 chassis. 2.3 motor. It ran hot too, so I installed a 70 degree c. thermo, and then I got rid if the electric fan ,drilled through fan into the pully and now it spins all the time like a conventional fan. I suppose some may not subscibe to this , but hey it runs cool now!! Dave
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Old 12-13-2001, 06:27 PM
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Well, did you R&R your fan clutch magnet? Did the new magnet fix your problem? I'm curious if you've resolved your overheating problem.

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Old 12-14-2001, 06:11 PM
Registered User
Join Date: Aug 2001
Location: Toronto, Ontario
Posts: 33
Another item to check....

Make sure that the thermostat is positioned correctly. The hole of the thermostat should be placed at the highest point to allow any trapped steam/air to escape.
190E 2.3, 1988
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Old 12-14-2001, 06:48 PM
ymsin's Avatar
Driver, Mercedes-Benz
Join Date: Feb 2001
Location: Malaysia
Posts: 1,645
From what I have read, I am sure the fan clutch is the suspect. The coolant mix-ratio will not influence the rise in temperature as much as a faulty fan/clutch would.
... Kerry

126 tailed by a 203, 129 leading the pack.
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Old 12-16-2001, 11:31 AM
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Cool Thanks to all. Here is an update

Update info,
1.) Again coolant is 60% water and 40% coolant

2.) The viscous-coupling fan clutch:
- it spins one third to one half turn with a Single push
- it speeds up when the engine RPMs speed up
- not sure if the fan clutch is allowing the fan to speed up
when the engine temperature is increases and the engine is
at Idle speed. (what is the best
way to check this? there is no obvious increase in speed from
visual observation)

3.) the electric fans are pushing air towards the engine (e.g air flow in the correct direction from both the auxillary fans and the fan clutch.

4.) Thermostat opens when boiled

5.) thermostat is postioned in the correct position ( I checked this multiple times.) The car was not overheating prior to the changes made, that is why I question if I damaged the fan clutch assembly or have not installed it correctly when replacing the water pump (I changed the water pump because it was leaking) This also suggest that the auxillary cooling pump should be working (e.g. I have monkeyed with it and it was previoiusly working)

6.) The block is filled ( I filled it up so that there was fluid leaking from the second opening then tightened down both of the nuts). Is there another way to make sure that air is not trapped)

7.) I change the tensioning device to ensure the appropriate tension on the v-belt.

How do you check to make sure that:
- the auxillary water pump is working
- there is no air in the system
- there is no pluggage in the radiator
- the viscous fan clutch is working appropiately

I have found that after running the car such that the temp rises to 80 dergrees C, and let it Idle. The temp begins to creep up rather quickly up past 100 C (it will overheat if I let it go). The auxillary fans kick on but does not cool the temp down. If I then rev the rpms to 2000 the temp quickly decreases to 85-90 within 30 sec to 1 min. The radiator is heating up approppriately (e.g. appears to disipating heat appropriately. The radiator also cools down after the aux fans have kicked on and I rev the rpms up)

I suspect that the causes are either the fan clutch assembly or the auxillay water pump.
I suspect that the most likely culprit is the fan clutch given the above findings and the fact that I took it off to change the water pump (e.g. I broke it or did not put it back together correctly)
However, it does seem that if there is not enough coolant flowing when Idling that this could also contribute. I would like to know how to test the auxillary pump without having to change it.

Thanks again for everyones help.
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Old 12-17-2001, 01:46 PM
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Aaron_190E, et al,

My fan clutch magnet was replaced but there is still no resistance when I give the fan a light push. Even with the engine running, I can manually stop the rotation of the fan. I'm suspecting a bad sender. BTW, my auxiliary fan is always on from start up to shut down. Despite the non-functional fan, the temps never get higher than 95. Any other ideas on what to check? Thanks all.

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