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Discussion Starter · #1 ·
At Ambient ~27C +/-10C
My 1985 500SEL runs around 60C
My 1986 560SEL runs around 90C

Is 90C high?
 

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81' 300SD, 82' 300D
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Your 85 sounds like it's running low. You should be around 80C. The 86 sounds like it could stand to run a little cooler, but it sounds ok to me.
 

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Your 85 sounds like it's running low. You should be around 80C. The 86 sounds like it could stand to run a little cooler, but it sounds ok to me.
 

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Smoke Silver '87 560SEC, Black Pearl '87 560SEL
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It depends on which thermstat is in there and you can't tell without disassembling the t'stat housing. Also, the thermostatic (viscous?) clutch on the engine fan makes a difference too.

My '87 560SEC and '87 560SEL both run around 90 degrees C unless it's hot outside, then the engine temperature in C is pretty close to the outside temperature in F (105F ambient gets around 105C engine temp, well within tolerance).
 

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1991 300 SE
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The condition of the aux fan is important as well, at least in the South. If it’s not running the car will over heat even with everything else in good working order; sometimes the aux fan just dies or the aux fan temp sensor set for 212 F stops working.

The 500 SEL settles in at about 95 C, the 300 SE at about 85 C.
 

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Discussion Starter · #6 ·
Assume I know nothing (won't be far from the truth).

(1) The main engine fan (the one on the front of the engine) spins when the engine is running, I assume there is some sort of clutch. I assume as the engine heats the fan clutch engages more firmly. Correct?

(2) The aux fan (the one behind the grill and on the exterior and in front of the radiator) does not seem to ever move. I assumed it would turn on if I used the AC. My AC does not work at this time and I have no call for it. Should this fan turn on at some heating point, perhaps when the engine temp rises above 80C?
 

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1987 & 1991 C126
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Ben,

RE: (2) The aux fan (the one behind the grill and on the exterior and in front of the radiator) does not seem to ever move. I assumed it would turn on if I used the AC. My AC does not work at this time and I have no call for it. Should this fan turn on at some heating point, perhaps when the engine temp rises above 80C?

I think you'll find the Aux fan won't work if the A/C is low of refrigerant. Certainly was true on my 560 last Spring while in Atlanta traffic.

60C or 140F is too low for a correct operating temperature.

Cheers, MBL
 

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Discussion Starter · #8 ·
MBL87560SEC - 4/3/2006 12:29 PM 60C or 140F is too low for a correct operating temperature. Cheers, MBL
Good to know, thanks. --Ben
 

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Hey, Ben. The first thing I might check is the temp. sender unit. They are fairly cheap and can be replaced easily. I assume this as this happened to me in the 300 when my gage was erratic but the engine showed no characteristics of overheating. (retarded timing, excessive heat, aux. fan running on high speed.)

You are correct on the viscous fan's operation. Engine bay heats up, clutch engages more to turn the fan more.

The info on the aux. fan not running with enough refrigerant is correct. However, the fan will run if the engines coolant temp reaches about 110 degrees Celcius. (230F?) And then shuts off the fan after the coolant cools off some. (around 95C-100C?)

If you show no signs of actual overheating, I'd replace the guages sending unit.

My $.02
 
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