Hey everyone!

I have a 1995 e420 and am having some issues with the engine running cool. I'm in MN so the temperatures are now hovering around zero and my engine no longer reaches 80. It comes up to temperature if left at idle but as soon as I'm driving the temperature drops to 60 and stays there until the car comes to a stop again. This tells me the coolant is running in open loop pointing to the thermostat being bad. This weekend I replaced the thermostat with an OEM Thermo from the dealer. Same problem. My question is, could there be ANY other reason other than the thermo as to why the car is running so cool? My guess is that I might have gotten a faulty part but I don't want to assume anything until I've at least reached out to the community and gotten a little input.

Thanks in advance for your help!!

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1995 E420
1998 SL500 Sport
2009 E350 Sport
1995 S500 Coupe
1992 500 SEL

my w140 drps during cold spells,and at 0 runs at 60c also.Its just normal I guess,I have a 170f thermostat,on purpose for hot summers and mountain driving

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

This thread may help you..

Heat Issues - Mercedes-Benz Forum

Martin

Doing some more research...came across this post:

"Just had the exact same problem on a '97 S500. Temp was very slow coming up and rarely got above 60 degrees centigrade. A new thermostat fixed it. Now it warms up faster and the gauge goes up to a hair width above 80 degrees centigrade and stays there. The climate control is much better as well, especially on days like today when it's 8 degrees Fahrenheit!"

Also, could it be an issue with the duovalve?

Thanks again!

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1995 E420
1998 SL500 Sport
2009 E350 Sport
1995 S500 Coupe
1992 500 SEL

Have you tested the value of the wires leading to the gauge? Maybe the gauge is reading wrong? Tested the resistace of the coolant temp sensor?

Could you increase the concentration of your coolant to water to maybe 80/20? Maybe that would help.

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1990 190E 3.0L

Car still comes up to temp at idle so I don't think it's the temp sensor. Does the coolant ratio affect thermo function?

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1995 E420
1998 SL500 Sport
2009 E350 Sport
1995 S500 Coupe
1992 500 SEL

coolant ratio will affect the cooling properties of the fluid. I think at a mixture of 8:2 you will run a bit hotter. I wouldn't go much higher than that otherwise I think the antifreeze may actually become semi frozen at low temps

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1990 190E 3.0L

Could the radiator be plugged at the bottom?