Thermostat Houseing Gasket

Chuck · 09-04-08, 01:16 AM

Just traced a coolant leak to the thermostat housing. I had installed it with a generic Ford 302 paper gasket. Not sure why it seeped coolant but it did. So now I need to consider options:

1. Another paper gasket. Since it leaked last time, not inclined to go that route again

2. Paper gasket with silicone sealant. ( I have a tube of Perma Tex thermostat housing sealant)

3. Silicone sealant with NO paper gasket. The directions on the aforementioned tube of Perma Tex seems to imply that no paper gasket is needed.

The thermostat housing is a generic type housing with the bypass opening, held in place with the usual two bolts.

The mating surfaces are smoothe and even. No imperfections, scratches, etc visible.

Cliff Beer · 09-04-08, 01:52 AM

Chuck, you probably need a little better gasket material - try a search for "High-Temperature Gaskets" at www.mcmastercarr.com and you'll find some choices there. Also, perhaps put a flat edge on the two faces to ensure you have perfectly flat surfaces. Finally, I have had good results with Permatex Form-A-Gasket -worth a try.

Jac Mac · 09-04-08, 08:00 AM

Chuck, is that the cast housing that you welded & reworked? The by-pass fitting looks like it is glued or bonded into the housing, maybe the heat from the weld failed the seal or could there be a pinhole in the weld?

Chuck · 09-04-08, 08:46 AM

Jac Mac:

You have a good memory. That is exactly the cover we are using.

Good observations. But we saw the coolant coming from the bottom of the housing where it and the engine meet when we ran it last night. Took the thermostat housing off and the lower portion of the gasket seemed soaked through from inside to outside. The rest of the housing was dry. So I don't think we have any leaks in the housing, per se, or in the bypass fitting.

The mating surfaces are flat and smooth.

The gasket was a cheap blue paper variety from the local Auto Zone.

I am really wondering if I really need a gasket at all in this application, or if a nice bead of sealant is sufficient. Is a gasket really required with a good bead of sealant?

Big-Foot · 09-04-08, 09:53 AM

Chuck - I think this is another case for the Permatex "Right Stuff" gasket in a can. If your surfaces are clean of all residue, the "Right Stuff" is all you need and it will not leak.

Just make sure it has had a good time (overnight) to cure before putting it to work..

Pat Buckley · 09-04-08, 11:04 AM

I would use a gasket - the local NAPA stores sell a gasket that is pretty durable that has adhesive on one side.

CRASH33 · 09-04-08, 11:06 AM

In my experience, silicone can almost always be a direct replacement for a flat gasket, so long as gasket height isn't an issue in the assembly. Don't over do it and do what some others have also suggested, which is to let it tack up before torquing, and let it dry for at least a few hours before putting it in service. Good silicone will fix many a issue with leaks when used properly.

If you want to use the paper gasket, try spraying it with Perma Tex Copper-Kote. That stuff works great too.

Molleur · 09-04-08, 11:36 AM

Agree with the silicone solution to stop the leaking. Have done this with SBF and SBC waterpumps successfully every time.

Rob · 09-04-08, 01:03 PM

Hi Chuck,
In my note this morning, I forgot about the modified housing. (clearly jac mac's memory is better.. :-) I would first confirm that the housing is true. Set it on a hard flat surface or scuff on flat paper or flat file etc to confirm it is true. Once this is confirmed, I use the paper gaskets but put a light film of blue permatex RTV, spread with my fingers. I always have good luck with this method. Haven't had a leaker in years.

Rick · 09-05-08, 03:39 AM

Big Foot has the right answer. Silicone "Flows" too easily when clamped, because there are no Binders in it as there are in "The Right Stuff". Use it once and you'll forget what silicone is or was............no comparison.

Chuck · 09-06-08, 12:34 AM

Thanks for all the good suggestions. Replaced the thermostat cover with a nice adhesive backed gasket. A bit of Thermostat sealant. Installed it, let it set up a bit, then tightened it down. Next day fired it up. Coolant again came pouring out, worse than before.

Turns out the generic housing we were using has an opening for the bypass hose that is nearly 3/4". The opening on the engine manifold is half that size. There just was not enough of an edge to seal it. Could have put a metal gasket with a smaller hole in place but decied to try a different approach.

Long ago ordered a CSC swivel thermostat housing. Nice, machined, aluminum piece with O rings instead of gaskets. Did not think it would clear the fire wall when we got it months ago, but decided to try it anyway. It fit well. Better yet, it did not leak. Problem solved. And it looks a whole lot better than our welded generic unit.