Leaking thermostat housing, o-ring?

[och]

Hey guys. Last year my car started overheating, which turned out to be a bad water pump, which I since replaced.

But before I replaced the water pump, I first replaced the thermostat. I removed the plastic piece that connects the thermostat housing to the radiator hose, installed new thermostat and O-ring, and replaced the plastic piece. But when I did that, the coolant started to leak between the thermostat housing and the plastic piece. So once I replaced the water pump, I put some red sealant between the thermostat housing and the plastic piece. Well, it started to leak again from there. I just took the plastic piece off, and basically the red sealant came off easily from the plastic and from the metal. Needless to say im stumbled. Is there some kind of gasket I can put in there? Like I've said, the thermostat o-ring is new.

 

[Zuffen]

The thermostat itself has a black plastic outer ring that does the sealing.

Check that ring is still fitted to the thermostat or is undamaged if still there.

It it isn't there I would suggest replacing the thermostat with another of the correct type.

An O ring won't seal unless it has a groove to sit in so it is located correctly.

 

[och]

Problem solved... for now at least.

The o-ring that I previously used was non OEM. I bought the thermostat at a Lexus dealer, but they didnt have an o-ring, so I bought it at an autoparts store. I picked up an OEM o-ring this morning at a Lexus dealer, and it seems a bit thicker than the non oem. Replaced it, so far no leaks.