Leaking around the thermostat gasket

[steve_wilwerding]

For the last couple years, I have had a very slow leak between the thermostat housing and the block. I figured this year I would just replace the whole housing and gasket, as well as refill with new coolant.

Everything went fine today, and I got all of the bolts on the thermostat housing tightened. I filled up with coolant, and before I even started the car or bled the system, I noticed that the new thermostat gasket was leaking as well. So, I drained the new coolant.

What now? Is it a matter of getting some sealant and using that instead of the gasket? I'm sure the block is somewhat warped - should I try instead to get that smooth? Anyone run into this before?

Any ideas are much appreciated - the car is in the garage on stands until I figure something out.

[logray]

If it is truly warped, then I would clean surfaces using acetone/etc. then use some RTV very sparingly, then reinstall and let it cure overnight before refilling.

If there is a slight burr/casting artifact you could very very very lightly sand the surfaces using a sanding block and very light grit sandpaper.

And you are certain you are using the correct torque values?

The new gaskets and mating surfaces must be totally clean.

[JFP in PA]

We like to buff the surfaces of both mating areas with a Scotch Brite pad to make sure they are both clean and without any burrs. You may want to also check each mating surface with a good straight edge while they are apart. To date, with proper cleaning, buffing and a new metal gasket, and properly torqued, we have not had to use any sealant on these surfaces, which is as it should be

[machster]

Check and see if the pump itself is leaking down to the therostat area.