89 Thermostat Gasket leaking


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I have replaced the thermostat gasket it two times. Cleaned and scraped everything off ran the car no leaks and go back a day later and leaks when it sits.
Any suggestions would help! Thanks
Verify that the housing is flat/true. Especially around the bolt holes, the tend to get convex from over tightening so gasket surface doesn't get clamped evenly. Try lightly sanding it on a flat surface (glass) & you should see even marks across the whole surface, if not it will show the low spots that aren't touching.
I will check it. I put the correct torq setting on it. It has never been removed before this since it was new in 89. Thanks Doug!
They very often get distorted. Get something perfectly flat, and some adhesive backed 180 grit sandpaper and sand it down, and that will show you the high and low spots, then you will have to use a hammer and dolly or anvil or something to straighten out the flange. Also when going back together, I suggest a generous amount of right stuff RTV on both sides of the gasket, and let it cure overnight before filling with coolant.
See my comment in this previous thread #3

Note that when it comes to RTV, a thin coat is all that is recommended. Most fails come from using way too much.
Generally, I would agree that a small amount of RTV is best, these thermostat housings are extremely problematic, which is why I specifically recommended right stuff, and enough of it to make sure it fills in any gaps due to the housing being warped.
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Be careful if you are using an aftermarket thermostat. They wont stay in the housing and fall between the housing and block, and when you tighten the bolts it warps the housing.

That’s what happened to me so I flattened the housing and put an original thermostat that stays in place and no leaks.
See attached post for pictures of the reinforced thermostat housing i used to stop leaks.

Ryan at thunderbird sc shop used to sell the billet units, really nice piece but he's been out of stock lately .