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Old 05-29-2001, 11:02 PM
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New problem issue popped up today. Was driving home from work with A/C on - (1st time in a while as does not get too hot here). Had been driving for about 20-25 minutes at
freeway speeds (little or no hills) when I happened to glance down at the temp gage -- it was within millimeters of hitting the red overheat mark. Screamed a few expletives as I pulled to the right shoulder. Turned the A/C off and the heater on and heat gage started to lower. Drove almost all the way home before I decided to run a second test by turning the A/C back on -- sure enough the gage started to climb again. When I pulled into the driveway, I popped the hood (with A/C and engine still on) and noticed that neither electric fan was operating. Turned A/C and car off and decided I will address tomorrow. But curiosity got the best of me and about 1 hour later I went back into diagnose mode. When I turned on the ignition (engine not started yet), the fan (I don't know which one) went into high speed mode for about two seconds and then shut off. With engine and A/C both on, no fan movement by either fan.

Is one or both of these fans supposed to be on at all times with the A/C on?

What do you make of the short fiery "bust" of the fan(s) when I turned the key to "ON" after an hour?

Any help would be appreciated.

For now, I will just not use the A/C and just "Sweat it out"!

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Old 05-29-2001, 11:28 PM
Zoonhollis's Avatar
Diesel Fanatic
Join Date: Jun 2000
Location: Cary, NC
Posts: 551
I would think that ram-air at freeway speeds would overcome whatever cooling the aux fans could do. Are you certain that your engine temp sensors are healthy?
1995 E300 Diesel (Die Blau Frau)
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Old 05-30-2001, 12:15 AM
Posts: n/a
I failed to state that when I noticed the increased engine temp, traffic had slowed to 20-25 due to traffic.
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Old 05-30-2001, 01:33 AM
JimF's Avatar
'94 S500: only 793 sold!
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,924
check your antifreeze/water ratio for starts. Here's a recent post fyi. There's many more.

Water Wetter compatible?

The fans should do just what they did but should also run when either temp or A/C pressure rises as per above link.

So lots of things to check. Good luck.
Regards . . . . JimF
'94 S500 Cpe

Visit my Mercedes Web Page
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Old 05-30-2001, 02:04 AM
Snow bum
Join Date: Jan 2001
Location: Here and there . . .
Posts: 238
I will be interested to see the outcome of this problem. In other words, I apologize for this post, but it was necessary for me to stay updated as the replys continue.
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Old 05-30-2001, 01:37 PM
Registered User
Join Date: Apr 2001
Location: Hawaii
Posts: 147
A friend had a similar problem like this with a volvo.

Try checking your fuses. It may be blown but on startup it may have just enough juice to arc across the blown fuse to to give a short burst on the aux fan.

Hope this helps.


1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles
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Old 05-30-2001, 01:43 PM
Registered User
Join Date: Nov 2000
Location: Tribune, Kansas. I farm for a living. I fly R/C airplanes for fun.
Posts: 53
My aux fan didn't come on a few weeks ago when the a/c was on. I found that the voltage dropping resistor was burned out on my car. It is located on my 86 300E right behind the driver headlights and on the fender. I tested it by jumping across the terminals with two screwdrivers carefully so as to not short against anything else. Replaced the resistor and my fan worked.
Ron Miller

1986 300E
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Old 06-01-2001, 12:59 AM
Posts: n/a
Problem solved. Not by me, unfortunately . A friend and I worked on car for a while and I lost patience and took to my trusty Independent. He popped hood and probed for about 5 minutes and came up with following problems/fixes:
1) Water pump had very small leak (showed me the leak and
I can't believe I missed it. This was the primary
cause of the overheating.
2) Re fans not coming on, he stated that the sensor that
turns them on was faulty. He replaced.

He replaced above two items and did a cooling system service and I am happy to say that temp gage had not exceed much above 100 degree mark - with A/C on and 94+ degree Fahrenheit weather today in Southern CA.

Thanks for the help -- much appreciated.
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Old 06-01-2001, 09:08 PM
Posts: n/a
I'm back. Problem almost solved.

Got car back last night. Drove it to work this morning. Got out of work and found puddle of anti-freeze under the car (not large puddle but enough to concern me) Also, low coolant light on.

After adding coolant, took car back to mechanic. Water pump is leaking (maybe defective). He states that he has seen this before and that sometimes it takes a while for the seals to seat.?.

Has anyone ever heard this before?

Mechanic says to keep an eye on it and if low coolant light comes back on to bring back for another water pump replacement (at his expense of course).

Thanks for all of your advise -- It is much appreciated!
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Old 06-02-2001, 12:04 AM
Senior Member
Join Date: May 2001
Posts: 104
water pump

Once I had just finished a timing cover job on a 102 engine, was filling the radiator and coolant was pouring as fast as it could out of the weep hole. My boss say's "run the engine and see what happens" after about five minutes it quit leaking and no signs of one the last two oil changes. Surprised the c**p out of me!
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