W140 S500 coupe overheating
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Junior Member
Joined: Apr 2008
Posts: 24
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From: Las Vegas
S420
W140 S500 coupe overheating
hi guys ,i have a 97 S500 coupe and its over heats does any one know what i need to check first when it over heats , here is the problem, the car runs fine its has about 95k on it, you can drive the car all day just once in a while the car over heats and when it does it the temp goes to 120 then i need to stop . i dont want to start changing item not knowing if it will work , also even when the car is not overheating and is at a normal temp the front fans all ways run , and i know they are not suppose to cause i had a S420 before , never had this problem , cant figure out what is it , radiator? fan clutch? termostat? can some one help please
Newbie
Joined: Mar 2009
Posts: 4
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e320,e55.s600
Many things can cause over heating. With the v8's and v12's (s420 s500 and s600) there is a lot of heat in a small area to disapate.
1)First is a no brainer is the coolant level correct? look at the color of the coolant, it should be clear with just a slight yellow tint. if it's green you have aftermarket junk. If its like a chocolate milk shake you have toasted your head gaskets. when was it flushed last? It is very important to use MBZ coolant and to flush it every 2 years. I have seen many heads that were ruined by the wrong coolant.
If the level and color is ok next is the Fan clutch.
2)Fan clutch. To check it get the motor up to 80c, turn off the motor open the hood, be sure the fan is not spinning, the electric acc fans can keep it turning! look before you reach in. With your hand give the fan a good spin, it should not keep spinning, 1 to 1.5 revolutions it should stop. If it free wheels its dead, also look at the center of the fan clutch, often they leak and have dirt and oil packed on the clutch. if its leaking its dead.
3) The thermostat is not easy to check. In severe cases when its stuck closed the motor is hot but the radiator is cooler in comparison to the motor. If the coolant is good and the fan clutch is ok, it's safe to put your money on the thermostat.
4) If you have checked out the above items and they are all good yet the car still runs hot, You need to check the fuel pressure. If the pressure is low the motor runs lean, lean motors get hot. Fuel filter , fuel rail pressure reg valve and last the pump. You need to look up the pressure and have a guage to check it.
Good luck , take care of it NOW or you will be doing head gaskets and if you bake it to long you can fry the cats.
1)First is a no brainer is the coolant level correct? look at the color of the coolant, it should be clear with just a slight yellow tint. if it's green you have aftermarket junk. If its like a chocolate milk shake you have toasted your head gaskets. when was it flushed last? It is very important to use MBZ coolant and to flush it every 2 years. I have seen many heads that were ruined by the wrong coolant.
If the level and color is ok next is the Fan clutch.
2)Fan clutch. To check it get the motor up to 80c, turn off the motor open the hood, be sure the fan is not spinning, the electric acc fans can keep it turning! look before you reach in. With your hand give the fan a good spin, it should not keep spinning, 1 to 1.5 revolutions it should stop. If it free wheels its dead, also look at the center of the fan clutch, often they leak and have dirt and oil packed on the clutch. if its leaking its dead.
3) The thermostat is not easy to check. In severe cases when its stuck closed the motor is hot but the radiator is cooler in comparison to the motor. If the coolant is good and the fan clutch is ok, it's safe to put your money on the thermostat.
4) If you have checked out the above items and they are all good yet the car still runs hot, You need to check the fuel pressure. If the pressure is low the motor runs lean, lean motors get hot. Fuel filter , fuel rail pressure reg valve and last the pump. You need to look up the pressure and have a guage to check it.
Good luck , take care of it NOW or you will be doing head gaskets and if you bake it to long you can fry the cats.
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Joined: Jun 2011
Posts: 6
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94 s500 coupe
Yesterday my 94 s500 Coupe temp got close to 120 as I was driving in 90 deg temp with AC on. I stopped and put some coolant in the reserve container and drove about 15 mins. and the temp held at about 80. I then drove 45 mins and the temp still held at 80. When I was 5 mins from home I turned on the AC and the temp started to rise close to 120 before I cut the car off. I did notice that I hear what I assume is the AC fan kicked on as the temp got close to 120. I started the car this morning and noticed that the radiator fan was turning as soon as I started the car. Is this normal? I never paid close attention to it before. Also, could this be a thermostat issue? I'm aware of the test, but haven't tried anything yet. Just wanted to know if anyone else ran into this before?
Thanks in advance,
Troy
Thanks in advance,
Troy
Last edited by tdsilk; Jul 11, 2011 at 03:36 PM.
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Joined: Mar 2016
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1998 S500
This is the same problem that I have on a 1998 S500 with about 122000 miles. My radiator had a leak, so I changed it. Then I noticed it was over heating getting to about 220 at idle after driving for a while. I changed the thermostat and tested the old one. It opened fully with no problem. Ran for about a week with the new thermostat and still got too hot and runs about 197 with regular stop and go traffic. If I turn on the defroster the car would cool down to about 185. If I'm running on the highway, the car runs about 181 and as low as 177. The car has a 176 degree thermostat and should only run about 183 for a high temp. I use a ODBII adapter and an APP to monitor the car so the readings are what the computer is reporting, not the gauges from the dash. The only other things I can do is gut the thermostat housing but then the car would not get up to operation temperature.
