Thermostat housing leak

[Zach]

Howdy, finished up on a project. Had to take radiator out, coolant swap, water sending unit, etc, etc. decided it was a good time to replace thermostat housing gasket since the leak was pretty bad, this is the 2nd replacement. This time I cleaned both surfaces, rubbed rtv on both sides of a 3 dollar gasket. Held good for a week but I am now starting to see some seepage. How do you guys normally deal with this gasket, 3 times and no luck so far. Engine is a 77 400 with a chrome thermostat housing, I guess replacing the chrome for metal could be an idea lol. Thanks.

[TA301]

I went through the problem you are having a couple of years ago. If you are using the blue paper FelPro gasket, it is not going to work well. I used Permatex
water pump and thermostat RTV gasket maker to put the leak to sleep.

https://www.permatex.com/products/gasketing/speciality-gasket-makers/permatex-water-pump-thermostat-rtv-silicone-gasket-maker-5-oz/

[b_hill_86]

Another option, which is what I used, is a housing neck that has an o-ring built into it. I got it as a gift years ago and never installed it. It’s chrome and I’m not into the bling. On a whim, I tried it last year and it seals better than I could ever get with the factory water neck. You could probably paint it if you really wanted to.

[Zach]

I went through the problem you are having a couple of years ago. If you are using the blue paper FelPro gasket, it is not going to work well. I used Permatex
water pump and thermostat RTV gasket maker to put the leak to sleep.

https://www.permatex.com/products/gasketing/speciality-gasket-makers/permatex-water-pump-thermostat-rtv-silicone-gasket-maker-5-oz/

Exactly the gasket I am currently using. Seems to just fit incorrectly anyways. Do you use straight RTV, no gasket? Might have to try that soon, although pulling radiator hoses isn't fun and I am running out of cat litter.

Another option, which is what I used, is a housing neck that has an o-ring built into it. I got it as a gift years ago and never installed it. It’s chrome and I’m not into the bling. On a whim, I tried it last year and it seals better than I could ever get with the factory water neck. You could probably paint it if you really wanted to.

Heard about those while researching this issue, I assume it was an older car design, not sure if they were available for my year. Chrome goes well since W72 has chrome valve covers stock, other wise I wouldn't care. Will have to look into that more.

Thanks for the responses.

[TA301]

If you use the Permatex sealant, no paper gasket is necessary.

[nUcLeArEnVoY]

I'm pretty sure for your model year and mine, the stock thermostat housing has a "seal ring" built into the casting of the mating surface.

Even the service manual recommends to use straight RTV to keep a good seal, and it's what I ended up doing after not only trying the Felpro gasket, but also the Butler performance gasket - they both leaked. Just draw a 1/8" bead of Permatex Water Pump and Thermostat Housing RTV (there's an actual RTV made just for this), and be done with it. Won't leak a drip.

In fact, dude, do you HAVE a copy of the service manual? If not, PM me. Best resource you can have for owning these cars.

[Bluebandit]

The housing can get warped from being tightened over and over. Get some sandpaper, lay it on a flat surface and sand the gasket surface flat.

[Zach]

I'm pretty sure for your model year and mine, the stock thermostat housing has a "seal ring" built into the casting of the mating surface.

Even the service manual recommends to use straight RTV to keep a good seal, and it's what I ended up doing after not only trying the Felpro gasket, but also the Butler performance gasket - they both leaked. Just draw a 1/8" bead of Permatex Water Pump and Thermostat Housing RTV (there's an actual RTV made just for this), and be done with it. Won't leak a drip.

In fact, dude, do you HAVE a copy of the service manual? If not, PM me. Best resource you can have for owning these cars.

Don’t recall seeing a place for an o ring but wasn’t really looking. Will definitely try rtv next time I rip it off. And no, don’t have a copy of the service manual but need one just haven’t got around to it, I can pm.

Thanks for responses will definitely try straight RTV soon.

[SoupMan]

Zack,

What BlueBandit said is an easy thing to do and will ensure you have a flat surface. Mine had that problem.

RTV worked every single time for me. Whenever I pull the housing I use RTV and it works wonders.

As for the cat litter comment. Just drain half the radiator, then press on the hose to push as much fluid into the radiator. When pulling the housing, wrap a rag around it and it will absorb most of the fluid. This will limit the cleanup. Been where you are too many times and finally learned.

[Bluebandit]

Easy way to drain the radiator is to get some 3/8" clear hose and siphon some coolant out thru the fill neck. Much easier than crawling under the car and drops the level enough to remove and replace.

[Zach]

Easy way to drain the radiator is to get some 3/8" clear hose and siphon some coolant out thru the fill neck. Much easier than crawling under the car and drops the level enough to remove and replace.

Definitely going to try siphoning it since there isn’t a petcock and I don’t want to drain the lower rad hose. Thanks.