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Old 11-27-2012, 10:12 AM   #1 (permalink)
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Date registered: Jan 2003
Vehicle: 1987 560 SL, 1978 450 SL
Location: Howell, NJ
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380 SL Idle...

I just purchased a very low mileage 1985 380 SL, and it seems to be idling very high (1500 rpm). The engine fan is very loud. I am presuming the car will need a tune up as its has only been driven about 1k miles in the past 10 years.

Does anyone have a guess to why its idling so high and why the fan is so loud?

My brother is a mechanic, and he will be doing the tune up this week, but if there is something that I can address on his same visit I would like to jump on it in advance.

Thanks.
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Old 11-27-2012, 11:50 AM   #2 (permalink)
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Radiator fan...

The auxiliary fan is engaging immediately when I turn the key to the second position and will not turn off at all when the car is running?

Anyone know what would cause this?

Thanks.

Last edited by Clean Dean; 11-27-2012 at 12:09 PM.
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Old 11-27-2012, 01:22 PM   #3 (permalink)
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Vehicle: 1985 Mercedes-Benz 380SL R107
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Radiator Fan...

More than likely there is either a short to ground in the wiring circuit of the fan which places current on the circuit whenever the electric is on, or the thermo switch is shot. This is a fairly straightforward circuit trace diagnosis which should flech out the problem quickly. Before circuit tracing, try removing the leads from the thermo switch and run an ohmmeter across the termins with the engine cold. If you read 0 resistance there's your problem and replacing the switch should clear the trouble. If you show infinite resistance then check the wiring from between the fan and the switch. You will find a shrt in there!
-George-
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Old 11-27-2012, 01:30 PM   #4 (permalink)
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Thanks George ! Where is the thermo switch located?
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Old 11-27-2012, 02:30 PM   #5 (permalink)
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That car needs a serious tuning. Do that first. Check or better replace spark plugs, oil all filters.
As per AUX fan, just follow the wires. I would not be surprised if there would be a manual switch somewhere in the car (no thermo).
This would allow driver to start the fan when needed.


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Old 11-27-2012, 02:49 PM   #6 (permalink)
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Tried that, and still could not locate it. The car has only 20k miles and still wears its original Michelin Tires !!! I never checked the soft top until today, and its not only original, but NEVER used !!!
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Old 11-27-2012, 03:25 PM   #7 (permalink)
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Change those tires pronto! Riding around on 25 year old tires is a recipe for disaster.. even if they have plenty of tread left. As for the 1500rpm idle, search this site for '380SL high idle' and you'll find several likely causes, including the 'green wire' issue that caused in intermittent high idle on my 1985 380SL.

You'll want to flush/change every fluid in the car, including differential, transmission, power steering, brakes, coolant, and even the gas in the tank if that's been sitting a long time (running stale old gas through your car's fuel injection system could cause lots of expensive problems!)

Inspect spark plug wires; replace if brittle. Replace all fuses with new brass-tipped fuses, cleaning the fuse brackets with contact cleaner before reinstalling the new fuses (fuse box is by passenger's right foot behind little door). Install new filters: Fuel, air, oil, power steering, transmission. The A/C most certainly needs service, too, assuming you have plans to use it and not the open conv. top.

Avoid the MBZ 'stealer' and instead find a well-respected independent repair shop that specializes in Mercedes of your car's vintage.
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Old 11-27-2012, 06:27 PM   #8 (permalink)
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Vehicle: 1987 560 SL, 1978 450 SL
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Quote:
Originally Posted by nathanso View Post
Change those tires pronto! Riding around on 25 year old tires is a recipe for disaster.. even if they have plenty of tread left. As for the 1500rpm idle, search this site for '380SL high idle' and you'll find several likely causes, including the 'green wire' issue that caused in intermittent high idle on my 1985 380SL.

You'll want to flush/change every fluid in the car, including differential, transmission, power steering, brakes, coolant, and even the gas in the tank if that's been sitting a long time (running stale old gas through your car's fuel injection system could cause lots of expensive problems!)

Inspect spark plug wires; replace if brittle. Replace all fuses with new brass-tipped fuses, cleaning the fuse brackets with contact cleaner before reinstalling the new fuses (fuse box is by passenger's right foot behind little door). Install new filters: Fuel, air, oil, power steering, transmission. The A/C most certainly needs service, too, assuming you have plans to use it and not the open conv. top.

Avoid the MBZ 'stealer' and instead find a well-respected independent repair shop that specializes in Mercedes of your car's vintage.
Ha Ha !!! I have a Mercedes Benz specialist with over 40 years of experience. My brother will tackle easy things like fluids and parts changing, but diagnostics and more involved work is left solely in his hands. The local Mercedes Benz Dealership has mostly young kids who work there, and are great with working on the newer high tech model, but do not know anything about cars greater than 10 years old.
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