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Location: Israel
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Engine get hot when idle
Hi All
Still not feeling so well so I gave the car to my brother...I am such a good person  Until today, I always drove the car out side the city but today, my brother had to go somewhere in the city so he stood a lot in the traffic. He said that the engine temperature was very high while the car was standing. it was almost in the red area...it is strange since when I drive it on the highway, the temperature is in the middle even a little below. Only when I stop the temperature rises slowly despite that I have plenty of water and the electric fan is working. Could it be related to lean fuel mixture? I suspect that I have too much air in the system. I know that lean mixture causes the engine to heat but could it be the reason for almost over heating? Thanks!
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Porsche 928S 4.7L 1980 European redhead 
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07-20-2009, 04:20 AM
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Petie3rd
Join Date: Jul 2000
Location: Philly PA
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not a lean mixture but a good chance the thermostat needs replaced as well as the rear thermo seal .
If you have a viscous fan then that part is probably going bad
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07-20-2009, 06:20 AM
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Quote:
By the way, on what temperature the electric fan should start working?
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07-20-2009, 06:26 AM
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I had the same issue. Most likely the Clutch on the Fan. There is a great howto on how to rebuild it too.
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07-20-2009, 07:37 AM
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How do I know it is faulty? I dont know how to check it...
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07-20-2009, 08:07 AM
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I would go ahead and order your thermostat from 1 of the big 3 vendors, especially if you have no replacement history on it. It's very easy to replace.
You can kind of tell if your clutch is becoming weak when after warming your engine and then shut your engine and watch the fan, it shouldn't spin very freely when warm. It should drag more when your at normal engine temp.
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1981 Porsche 928 "Euro" Auto Gunsmoke Metallic Flat - Black Interior 1983 Porsche 928S "US" Auto Light Bronze (Copper) Metallic - Brown Interior **SOLD**
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07-20-2009, 08:12 AM
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Petie3rd
Join Date: Jul 2000
Location: Philly PA
Posts: 4,528
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viscous fan is the one thats on the engine ,and has a big finned center, this operates on temperature .
There is a small pin under the Bimetallic strip in the center of the fan, after carefully cutting the silicone thats holding the strip slide it to one side and then it will release from the fins. Once this is done then remove the small pin and examine it look for cuts on its shaft, you can dress it down a bit with some 400 grit I used a rubber tip of an air gun to hold the pin . I got a bottle of silicone oil at the Toyota dealer about 2oz and its 14.00 I refilled it and refitted the pin and the green seal. To test the fan when its cold there should be resistance to turning if it freewheels then the fluid has leaked out. If your replacing the thermostat make sure to also get a new O ring and the thermostat rear seal.
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^^^ Stan ^^^ 2019 BMW K1250 GS 2016 HD RK 1988 S4 Auto , Elfenbein Perlglanz, Pearl Gray 1982 5sp Met black and tan sport seats |
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07-20-2009, 09:18 PM
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Can you please tell me the Thermostat type that I should buy? I can probebly buy it in some local part shops instead of ordering it from USA.
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07-21-2009, 02:30 AM
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Quote:
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07-21-2009, 06:19 AM
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Most normal parts shops will give you a Mercedes Benz part with the wrong size Oring. This is a case of needing the correct part, and either knowing what that is, or using a vendor that does.
Make sure you get the replacement seal that goes in the water bridge as well. |
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07-21-2009, 07:41 AM
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I have checked the water hose that goes in and out the thermostat while the engine is hot and the temperature is the same....I have been told that usually when the thermostat is stuck - there will be different temperature on those hoses...what do you think?
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07-21-2009, 08:01 AM
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Using an IR temp thing I get about 195F going to the radiator and about 150F going back to the motor from the radiator. If the temps are about the same the radiator isn't doing its job, could be blocked or fan not working well.
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07-21-2009, 11:22 AM
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212 Degrees is the trigger for the electric fan. Switch is often refered to as the 212 switch.
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07-21-2009, 01:55 PM
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[QUOTE=Mrmerlin;4788516
To test the fan when its cold there should be resistance to turning if it freewheels then the fluid has leaked out.[/QUOTE] Addition to this statement. "More" resistence should be when the car is warmed up as this is what gives more air to the engine (cools it down). I guess the statement could be read both ways 
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Last edited by MPDano; 07-23-2009 at 09:53 AM.. |
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07-23-2009, 09:50 AM
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Quote:
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07-23-2009, 09:54 AM
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