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1985 500SEC
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613 Posts
Discussion Starter #1
My wife's 1991 420 SEL started running 10 degrees warmer than normal with flucuations on the gauge. My first instinct was to replace the fan clutch. That seemed to cure the flucuations but it still runs too hot. I talked to a reputable mercedes mechanic in Costa Mesa, Ca and he told me that 3 out of 5 new fan clutches are defective. When he replaces a fan clutch he buys used ones and has better luck. Any ideas out there? The car has no leaks and a new radiator. Thanks in advance.
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,290 Posts
Hi Minkoff,

Sorry to hear of your inconvenience.

Q1: Does this occur right after a cold start & then keep it up?

Q2: Does this hapen only at highway speeds? flow or radiator

Q3: Does this happen only in stop & go traffic? Aux fan/fan clutch

Many questions plus general observations, [:(]

Used fan clutch? NO, I don't think so. If your guy has problems with 60% of the new fan clutches he purchases, he really needs to find a different supplier/different quality f/clutch. German Star sells good quality products for example....

Cheers, MBL

Lest I forget.... How's the sender unit?
 

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1988 560SEL sold:
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4,717 Posts
Out of curiosity, at what range of temperatures?

I am somewhat concerned about mine since it used to be in 80-85c range and now, it's more like 85-95c range, mostly around 90c.

It is spring and ambient temperature may have effect on efficiency of cooling, but recalling JDC's post about his remaining a constant 80c at stop and go traffic in sunny Florida, perhaps there is something not completely right about mine.

The fan clutch and radiator are only a year old so I assume they are in good working order.
 

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1984 280SEL AMG
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701 Posts
1) check oil/change oil
2) do a radiator flush, then change the coolent, somtimes people put to much anti-freeze into the radiator... you should run a 70/30 mix water/coolant. Since your in CA, and the temps there are a bit higher. I'm in Washington, so I'd run a 60/40...
3) check your thermostat, somtimes as thermostats get old, they tend to go wacky.
4) check temp sender unit. it's a 1 or 2 wire thingie.. not sure where it's located in your car..
5) try new fan clutch
6) lastly ( and most coastly ) posably a small leak in your head gasket, not enuff to displace water/oil eather way. But enuff to raise temps.. ( not likly that tho )

Check things in that order. you'll find your problem... Always check from the least expensive to most expensive... Cause sometimes it's the cheap things we over look...


GOOD LUCK ON YOUR MISSION [:D]
 

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1988 560SEL sold:
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4,717 Posts
danwatt - 4/21/2005 4:49 PM

I live in Orange County too and I get constant 80C temps. Even while driving up the mountains on the 5 freeway with the AC on it still hovered near 80.
thanks for another performance benchmark. I will look into the list of things to check. I am hoping that it is the antifreeze/water ratio.
 

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1990 300SE
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1,466 Posts
Probably not. I've run only distilled water before and I still maintained 80C. Make sure you have the proper amount of fluid. Also, check to see if your radiator is blocked off (leaves, bugs, dirt in the fins)
 

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1984 280SEL AMG
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701 Posts
To both of you, check your elictric AUX fan... It's the fan right outside under the grill. See if it free spins, or has a bit of a sluggish feel... could be that's not working. That runs when the clutch fan isn't enuff to cool the engine... Tho realy, as long as the temp isn't hitting the RED LINE. Their should be nothing to worry about.


P.S. check your air filter as well...

remember cheapest to most expensive..
 

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1985 500SEC
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613 Posts
Discussion Starter #12
Because I dont have the time to deal w the problem I took the car to Bruce Strauss Auto care in Costa Mesa, CA. have not heard yet what the problem is but Bruce said its either the thermostat, or the aux fans not coming on when the air is on. I am betting thermostat
i'll keep you posted
 

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1988 560SEL sold:
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Nice to know the cause and have it fixed. I'm monitoring the engine temp. on my car and it has stabilized at 85-90C range. While on freeway, it's just above 80C so I am not too worried about it but will probably perform a preventative maintenance by changing the thermostat in August, when the annual take it to the shop with list of concerns is due.
 
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