Ditch that thermostat housing.

Get a Scott Drake repro or an original housing. The o ring and many other aftermarket chrome housings have sealing issues.

 

Thanks. I heard the flange on those were thin. Will let you know in a week!

 

I don't know what Permatex you're using but I'd opt for the blue RTV. Other forms of Permatex create a more permanent seal so that if you ever need to replace/fix a leak you'll destroy the gasket/seal.

 

If using an Oring type thermostat housing you don't put any sealant on it. I would just bolt it on and torque to proper setting. If it still leaks then I would go the original thermostat housing route.

 

O-rings do not need any sealant. The O-ring needs to fit perfectly in its groove and adding something else will cause a leak. Just make sure the sealing surfaces are clean and smooth. I recently made this mistake when changing a water pump along with a timing belt. Had to take it all apart and replace a $1 O-ring minus RTV.

 

Very helpful, thank you

 

When I installed my new ACP 2 row radiator i pulled the tstat just to see what was there. Both surfaces were excellent so I reinstalled the factory housing with a new felpro gasket and a very thin coat of HD red grease on each side. No leaks so far.

 

I had nothing but trouble and leaks with the O-ring type of cover. I replaced it with the original type and never had another problem. I also as recommended drilled a small hole in the top edge of the thermostat to help "burp" the cooling system or allow for some coolant flow while the engine was warming up, I forget which, maybe both.

 

Found this on Amazon a few years ago. Nice pc and has not leaked.

eClassics 64-70 Mustang Thermostat Housing w/Gasket, HD Zinc Cast, V8 289/302/351W Amazon.com: eClassics 64-70 Mustang Thermostat Housing w/Gasket, HD Zinc Cast, V8 289/302/351W: Automotive


Mark

 

I've made many thermostat gaskets with a utility knife and this: Fel-Pro 3157 Gasket Material

 

I made a water pump gasket out or a manila folder coated with RTV. It was supposed to be a temporary fix until I got a real gasket. Well that never happened and it never leaked.

 

I've yet to have trouble from a chrome water neck. When I get one I use a belt sander to remove the chrome and flatten the sealing surface though. A bit tricky to not chip the edge of the chrome where it shows but it can be done with care.

 

I put a chrome Mr.G. thermostat housing on my "new" engine. I also installed a Tefba inline coolant filter. My filter was constantly clogging with fine granules of something. Since I had built my engine with a brand new Ford Racing block I thought maybe it was casting sand still in the water jackets, But it never stopped clogging the filter. Finally in a moment of desperation I pulled the thermostat and immediately noticed that the Mr.G. housing was "shedding" internally. I don't know what kind of crap pot metal they used to make that thing but it was junk.
I replaced it with this part from O'Reilly. It seals perfectly and it has an additional NPT bung into which I installed a sending unit for a red "Coolant Hot" warning light.

https://www.oreillyauto.com/detail/b/murray-climate-control-4379/cooling---heating-16773/thermostats-25043/thermostat-housing-water-outlet-11367/605bb129430b/murray-climate-control-water-outlet/84831/4523057/1965/ford/mustang?q=84831&pos=0

 

I put a chrome Mr.G. thermostat housing...

I have long sworn off ever again using anything that bears the "Mr.Gasket" label on it.

 

The Mr. Gasket brand was bought by Holley in 2015. It is Holley's lowest priced brand. It was a brand owned by MSD (my spark disappeared) when Holley bought MSD in 2015.