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Old 10-30-2000, 10:41 PM
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I hope someone can help me with my 98 C280. I have owned it since it was new and I take methodical care of it. However, About a month ago, it started running hotter than it has at any time in the last 3 years. There is no apparent damage to the radiator or cooling lines and all frontal shrouds are in place. The temp has never been above an indicated temp of 80-85C. Now, the Temp is always 85-95C. The electric fans now run in high speed a lot more often than they use to and the front right quarter panel is extremely hot to the touch. I verified with a calibrated temp meter that the temp of the top cooling line at the engine is running between 88-93C at idle with an ambient temp of 75F and AC on. The dealer has replaced the coolant tank cap, flushed the system and changed the thermostat. Oil level is in spec. (Mobile 1 10-30). The dealer states that that temp is in spec for my car and are happy with the way it is running. However, they have no explanation why the outside front right quarter panel is so hot or why the temp is indicating higher and why the cooling fans are running more often. The car has never had any damage or mods done to it. Any suggestions would be appreciated. Should I insist they change the water pump? The car is still under warranty. Thanks!


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Old 10-31-2000, 02:39 AM
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Join Date: Oct 2000
Location: Taiwan
Posts: 21
This is a common problem as many professinals talked here. You may have a burned fuse in the low speed fan relay.
Here is my experience on C220.
Find the relay box under the hood in driver side right next to fuse box. Screw off 5 screws then open the cover. You can see a relay with 15A fuse, this is the one for low speed fan. Replace it with 25A or 30A cause 15A is too conservative for the current the fan consumes.

I also know it from this great site. Thanks to all who contribute to this site.
I am so glad to have my first post here.

1994 C220
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Old 11-12-2005, 05:42 PM
clankford's Avatar
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Join Date: Dec 2003
Location: Mesquite, TX
Posts: 134
'98 C280 - looking for coolant fan lowspeed relay?

I know this is an old thread, but I seem to have the same problem. My '98 C280 runs about 90c to 94c and the coolant fan is either full on or full off.

I tried to use your description to find the lowspeed relay/fuse, but mine has several fuses and relays in the described box!

Can someone with a layout tell me which relay and fuse is which?

Thanks again guys!

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Old 11-13-2005, 01:47 AM
Ali Al-Chalabi's Avatar
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Join Date: Nov 2000
Location: Knoxville, TN
Posts: 1,837
In '98, the fans are no longer limited to low speed/high speed. Electric fan speed is infinately variable and based on coolant temp and refrigerant pressure and is controlled by the Motronic control unit.

On the '97 model year, the lowest trip point based on coolant temp was 95C. 90-94C is normal, I would be concerned if the temp did not get to the 90-95C in traffic, because then something would be wrong.
Ali Al-Chalabi

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Old 11-13-2005, 02:48 PM
clankford's Avatar
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Thumbs up

Thank you so much for the information!!!! I feel better now!

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Old 10-20-2007, 10:12 AM
Tony P.
Join Date: Jun 2007
Location: Near Atlanta Georgia
Posts: 7
Thumbs up

Charles was right on the money with my problem - Thanks!

Hi everyone! Just an update - I have a 1995 C280 with only 63k miles and have been having the same coolant temp problems since I purchased the car a year ago. I went through all of the normal updates: new thermostat, flush and drain, even purchased from JimF the "cool harness" - but the real symptom never changed.

There was another post (Charles ) where someone mentioned that in the low speed fan circuit for his 1994 C220 - there was a relay that controled this circuit in the section "behind" the fuse box on the drivers side of the engine compartment. This relay has a "piggy-back" fuse installed at the factory as a 15A fuse. The indication was that the fans draw over 20A at times and that a 25A or 30A fuse should be placed here.

When I looked - that was my problem - a simple fuse replacement would have solved the problem.

Here are the symptoms:
1) At some temp the low speed fan circuit should turn on the fans and they should run continuously until the temp gets low enough to turn them off - or - the high speed circuit kicks in.
2) If your fans only turn on and of in high speed and typically stay on only for 20 seconds or so until extreme high temps are reached (110-120 degrees C) and you never see a slow speed fan condition. CHECK THIS FUSE
3) Most of the time the temp stays between 85-95 degrees C when operating at speeds of 30 MPH or more, but then in stop and go traffic - or low speed driving - temps can move up to over 100 degrees C and stay there until "something changes" (no clear indication of what made the temp go down). CHECK THIS FUSE
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1998 C280 Temperature running higher.-im000003.jpg  
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Old 05-19-2008, 11:51 PM
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Join Date: May 2008
Posts: 3
1999 C280 Radiator cooling fan

My cooling fan runs only at the slow speed is there a fuse or relay that is bad??
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Old 05-20-2008, 03:57 AM
thevtechater's Avatar
Join Date: Jan 2008
Location: West Java
Posts: 40
slow speed only? that's new.
u should really check the fuse on 'em.
coz the low speed fan is usually triggered only by the refrigerant pressure and not the water temp.
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Old 05-20-2008, 09:05 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
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Engine cooling fan is computer controlled. Most likely a problem with that control unit.
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Old 05-20-2008, 09:05 PM
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Originally Posted by ralph spears View Post
My cooling fan runs only at the slow speed is there a fuse or relay that is bad??
Is there a problem with your temp? If the temp is fine then that could be why the fan only runs on the low speed.
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
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Old 05-20-2008, 09:40 PM
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Engine cooling fan

I have owned this car since new, it runs at 90c when you stop for a traffic light the temp starts to climb and when you start moving the temp comes down. The high speed fan never comes on like it used to.
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Old 05-21-2008, 11:11 AM
david s poole
Join Date: Mar 2005
Location: dallas
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if your car heats up at a stoplight and then cools down when you take off again,[assuming that the cooling circuit is full] the radiator tubes might be shrunk.
David S Poole
European Performance
Dallas, TX

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Old 04-05-2011, 02:02 PM
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Join Date: Apr 2011
Posts: 1
Hi, I have a 94 C220 and sometimes in the morning when I first start it the cooling fan comes on. Ill drive it for a little and it may turn off. The temp is fine, no strange changes. Could this be a fuse?

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