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