On my 1984 Fiero since the first gasket failed after running, I have tried twice to put in a new thermostat housing gasket. The first time, I used grey gasket maker for thermostat housings and thread sealant for the bolts, and it leaked. And now today I put another new gasket on without sealant by recommendations on another group, and the damn thing is dripping coolant again. I cleaned both mating surfaces throughly with sandpaper and cleaned them after with a paper towel.. Is there a guaranteed method to get this to work?



This is what the newest leak looks like, both times it was from the bottom. The first replacement worked before I ran it, then it leaked, but this one just leaves right off the bat. I torqued the bolts to 22 ft/lbs spec and used the right gasket for my duke. Any help?

There must be a bit of unevenness somewhere.

Probably the best bet is to paint the gasket with Permatex's product.
This stuff usually works so well, you have to scrape both surfaces clean if you can get them apart.



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[This message has been edited by fierosound (edited 02-10-2021).]

The "gen1" T-stat housing is Weak and once the flange is damage won't seal or leak soon after.

Pull off and look a flatness of the flange. Use anything flat, light one side and look thru light at other side.

ReRead your first //www.fiero.nl/forum/Forum2/HTML/144700.html and search PN for "gen2" w/ better flange in //www.fiero.nl/forum/Forum2/HTML/144348.html

If you keep damage "gen1" part.
Carefully Flatten the Flange.
Then use longer bolts and make spreaders to load the housing better then old holes.
Some flat iron w/ 1 hole spanning the whole piece maybe including bent edges might make it work.

Use a New gasket and use High Tack or Super 300 and paint both sides.
Sealers won't work w/ any wet gasket. Most times No even if dried out.

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quote Originally posted by fierosound: There must be a bit of unevenness somewhere. Probably the best bet is to paint the gasket with Permatex's product.

Agreed, although I favor a slightly different product from the same family... Permatex Aviation Form-A-Gasket. I've been using this stuff for almost half a century!



Make sure the ends of the thermostat housing flange (where the bolts go through) have not been bent "down" from tightening the bolts.

Sadly Above isn't available in many places. Supper 300 is close to same and an "off the self" right now at more stores.
I've used both and works same.

Both are better w/ iffy surface(s) that need a little to fill small divots and scratches.

I'd echo everything Ogre said... the same problem affects Ford 2.3l motors, and those are the solutions. No amount of sealant will fix a warped housing forever. If replacing it isn't an option you need a big sanding block to get it pretty flat and then load spreaders to keep it tight.

I'm in Patricks corner. Aviation form-a-gasket will do the trick. On the other hand there is a product called "Indian-Head" gasket sealer. comes in a brown bottle. Be sure to use a new thermostat because the odds of getting this apart in the future is slim. Guaranteed not to leak even if you forgot to insert the gasket!



Spoon

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I had this issue on the 84. Previous owner overtightened and bent the flange. I used gasket "Felpro 35562 T". It is a hard plastic gasket with a rubber o ring. Install dry, no sealant. The bolt holes have to be elongated with a file to fit. Never leaked a drop after two years and multiple removals. No overheating issues. If the flange on the housing is corroded you must clean it good.

This is the exact item I used: https://www.amazon.com/Fel-...asket/dp/B000C2E4GM/