My vehicle is a '91 300-SEL - M103 engine. The car is fine at the moment. I have a cooling system question I'd like to confer with other list members about.

I've heard that if revving the engine of an overheated vehicle reduces the engine temp, the thermostat is defective?

Is there any truth to this? If not and revving does reduce engine temp, what does this indicate? Thanks for your time.

Mike Murrell

The best way to test t/stat is to remove it & put it into pan of boiling water. On all MB t/stats there is a marking that states the opening temp. Make sure that it opens completely. If this checks out then you have another problem.
A new t/stat with every coolant flush is $$$ well spent. Running w/o t/stat will allow engine to run too hot in summer weather & car won't perform as well over the life of the engine.

This may sound simple, but I had a similar symptom that turned out to be low coolant.

- Nathan
'83 240D

When you "rev" a hot engine, a couple of things happen. If the fan is working properly, it will be clutched and will pull a ton of air through the radiator. At the same time, the increased RPM's will produce a higher circulation of coolant through the radiator. The sum total of all this is the coolant temp will drop at a greater rate than it would at idle. The increased air flow will also move the latent atmosphere under the hood as well, contributing to the overall cooling effect. Of course, none of this will happen if the thermostat is not working properly. Hope this helps..

------------------
Jeff L
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 04-05-2000).]

Jeff - thanks a bunch for your very informative reply....makes sense.