My '90 300SE with 245K on it is running warmer than I think it should. Symptoms are:

Driving at HWY speeds, temp about 85-90C. As soon as I stop for longer than a minute, temp goes to 100C. At a long light, or heavy traffic, 110C+. Then, the fan comes on and temp quickly begins to drop, or I start moving and temp drops. Also, after a breif shut down, for gas ect., upon restart, temp jumps to 110C then drops quickly. Ambient temp around 90F

Coolant level is good. A/C works fine except for a breif perid last week that Benzmac thought might be a problem with the low speed fan. Since then, A/C works fine.

I do have an exhaust leak at the head/manifold, I don't know if this is related. I'm off again tomorrow to Dallas, and would appreciate promt responce. I did not own this car last summer, but these temps seem abnormal.

Thanks

I have seen this problem with a thermostat that only opens a crack. It is ok on the highway but when you get in traffic the temp gauge creeps up. Pull out the thermostat and boil it to verify that it opens all the way and at the right temperature.

Thanks for the reply. I had a new t-stat laying around so I went ahead and replaced it. That seems to have cured it...but it's only 75F out tonight.

Before I changed it, I noticed that with the engine cold, the upper radiator hose was still full. Am I correct that it should be pretty empty when the engine is cold?

To replace it, I just opened the housing, replaced the t-stat, buttoned it up and refilled the tank. I hope that's OK.

My 300D sometimes behaves the same way, and its thermostat is only a month old. I have heard of these thermostats being defective right out of the box, but I'm still not quite assertive enough to demand that my mechanic replace it again. I will be interested to hear the outcome of your problem.

[Edited by Ben300SD on 05-30-2001 at 02:12 AM]

Hi There:

I had a similar problem with my 260E. I replaced the thermostat and the problem persisted. I thought it was a problem with the thermostat and I drilled a small weep hole in it to test it and it did cool the car down a lot. That indicated that the thermostat was only opening part way.

Got a replacement for the deffective thermostat and the replacement works fine.

Good luck with your repairs!

Aloha,
Eric