I replaced my thermostat last week due to overheating. This fixed the over heating problem but now... my car leaks all the coolant out when it is left shut off over night. It only happens after the car is sitting parked in my driveway for a while. every morning I have been putting more coolant in just to get to work and it doesnt leak unless its sitting for a while.

Some things to keep in mind. I was only able to replace the thermostat at the time not the o-ring b/c it was sunday and i couldnt find one. Also I have never done a thermostat replacement before but all i did was pull the old out and put the new one in, which was about 17 bucks at autozone. I am pretty sure the leak has something to do with this since it wasnt leaking before. Any help would be appreciated. THANKS!

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2004 CLK500
2000 S500

cannnot reuse the o ring , it will leak, start over clean all surfaces and replace all gaskets and o rings

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Jerry

2004 SL500 Black 55K Miles
2002 s500 Black 90K Miles
1986 300E Gold 233K Miles
1966 Twin Cessna 320D
1989 Jeep Cherokee 233K Miles
1994 Ford Van E150 399K Miles

Auto Zone parts are pure junk. Get a real part for your MB.

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'91 300-SEL

like i said, i was in a desperate situation... car over heating on sunday before fourth of july, no where open but autozone.

i will redo the job but do you guys think i really need a MB thermostat or just an O ring and to clean everything up better. I bought some silicone too so i guess i will use that around the edges.

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2004 CLK500
2000 S500

You don't need silicone. You might get away with a new gasket, but I would not trust my MB engines health to anything provided by Auto Zone.

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'91 300-SEL

by overtorquing the bolts. New O' ring should do the trick.

JB

just take that one out and put the cover back together and snug it down it will probably stop leaking because the preasure will be off...

go ahead an order a new one from this site....

and put it in around the end of september...

Maybe it's too late, but I've heard that when you install new thermostat you should look at the old one's orientation. There is a mark. Then make sure the new one's mark is pointing the same way. I have no idea why this would make a difference, but I've always done it and haven't had a problem.

I'd order the thermostat and O ring from Fastlane [this site] .. they ship like super fast -almost next day and their prices are very competitive...

Are you saying to drive around without a thermostat for the time being? Isn't that bad for the car and won't it still leak... Sorry if I sound dumb but this is the first time I have had to deal with the cooling system

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2004 CLK500
2000 S500

Do not drive without s t-stat. Bad advise.

Engine mgt. systems pick up sensor info..ie..cooling temp sensor. If your eng. is cooler than it should be, you'll run too rich.

Once again, go get a real MB t-stat and gasket.

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'91 300-SEL

okay I replaced the thermostat and o-ring with original MB parts. I usually order from fastlane but i needed this in a hurry so sorry to the guys who run the site.

The leak is still there. I beleive I have pin pointed it with pictures. I still think it has to do with me replacing the thermostat b/c it didnt leak before that, but my engine did overheat the day the old stat went out so maybe that caused it.

I have attached pics of the problem area, there is a little puddle of water/coolant in the red circles, the last picture shows it best. I see the liquid dripping but its difficult to see from where exactly. Let me know what you guys think.

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2004 CLK500
2000 S500

after some further investigation it seems as though it may be the water pump that is leaking the weird thing is though that it doesnt really leak when its being driven. only after you drive it and then shut down the engine does it leak. not sure if this is a bad pump or just a hose or something i pulled loose while changing the stat

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2004 CLK500
2000 S500