Low heat in a w126
 

In a 1989 420 SEL, if I do not turn on the heater, the engine temp gauge shows 80, which is the proper temp. after a highway run. However, if the heater is turned on, the engine temp only reaches 65 or 70. Also, with the heater on max. heat and high fan, the inside temp. is not really hot.

The temperature outside is -20c. Is it a bad thermostat?

I would think so.

Had the exact problem in my wife's 560SL we had bought a month before.

Bought a new thermostat assuming the old one was stuck open. Previous owner had totally removed the old one!

From what I heard, MB thermostats fail by sticking open rather than closed like other cars. The result is exactly what you're experiencing.

I'd get a new thermostat in there ASAP. By the way, don't buy it at MB Express in Etobicoke.. you don't want to know what those things cost at dealer prices /how much I paid for mine at MB Express...:eek:

Neal

Order it from fastlane at the top of the page. Over time, the thermostats generally start to open at cooler temps as they age.