I have a '92 300SD with 367K on it and it still runs like a top, except that it has the perennial overheat problem. I put a new radiator (leak at upper hose neck), radiator fan (1, broken mounting frame), and water pump (it's about time) in it in the last month and it still runs hot. I got a new thermostat along with the pump on the web but did not put it in when I did the pump for reasons I cannot remember. I tried to put it in today and found it was not even close to resembling the one I took out.

So I put the original back in and went to town to the Foreign Car Parts store and they had one for me. However, I live 20 miles from there and have to go over a big hill (usually drives the needle to halfway between 100° and the next mark) to get there. The temperature acted just fine all the way.

So, is it reasonable to think that taking the thermostat out and putting it back in might fix the problem? I'm not taking any chances and am replacing it anyway, but wondering why it might act in this manner.

unless you cleaned any scale or corrosion off the t-stat, there isn't much you could have done except maybe seal up some leaks or cause some more. Could have been in backwards and you replaced it properly... but thats a long shot.

Since you have already bought the new stat, put it in if its the last thing on your list. Your recent ride was most likely an anomaly.

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You said a new radiator and fan. What about the fan clutch? Or is that part of the fan. It won't make the difference on the road but it will around town.

Did you flush the system with the old rad in before you put all your new stuff in? What was the type of coolant and the mixture ratio. It makes a difference.

Definitely get the correct thermostat. The BEHR is not that much and you can get it on this site.

Also, if you have access to one of those cool thermometers you can check your actual temp. at the thermostat housing and then compare that to the gauge to see if you have any error.

Last but not least... If you have any air in the system, it will get hot. People here talk about putting the front of the car on ramps to help "burp" the system when filling. I did not have that problem. BUT, apparently it is a problem with some of these cars.

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AJ

1985 300D (SOLD)