GM 350 thermostat housing gasket leaking

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Nov 29, 2009
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Okay so I may have started a thread on this already, but I can't find it. Anyways, here are some updates on my thermostat housing gasket that keeps leaking. I verified that the housing is a steel housing and not aluminum, it is straight and not warped. This particular intake the housing bolt holes go all the way through to the coolant, so we found a special gasket that seals the bolt holes also, and it leaked even worse. I guess the next fix is just go back to the regular gasket and use rtv on it and around the bolt holes. We just have to drain the coolant in the block some to do that I guess to get it below the intake.

https://www.amazon.com/Mr-Gasket-738G-Water-Outlet/dp/B000CMF20O/ref=sr_1_10?crid=SUGC16JLVC5B&dchild=1&keywords=thermostat+housing+gasket+small+block+chevy&qid=1589413975&sprefix=thermostat+housing+gasket+%2Caps%2C175&sr=8-10

This is the expensive reusable gasket that leaked like a sive.
 
After coating the gasket and bolts with rtv (probably should have done it in the first place), i'm out of ideas if that doesn't work.
 
Last edited by a moderator:
Originally Posted by motor_oil_madman
Okay so I may have started a thread on this already, but I can't find it.

Click on your user name in the upper right.
Then click on your post count in the upper right.
Then select "Threads Created" in the upper right.

You'll find a nice list of every thread you've started.
Then you don't need multiple threads on the same topic.

BTW, you can see other member's post count and thread creation count this way too.
Motor_Oil_Madman has created 17 pages worth of new threads at 50 threads created per page, which seems like a lot...
 
Originally Posted by Imp4
Originally Posted by motor_oil_madman
Okay so I may have started a thread on this already, but I can't find it.

Click on your user name in the upper right.
Then click on your post count in the upper right.
Then select "Threads Created" in the upper right.

You'll find a nice list of every thread you've started.
Then you don't need multiple threads on the same topic.

BTW, you can see other member's post count and thread creation count this way too.
Motor_Oil_Madman has created 17 pages worth of new threads at 50 threads created per page, which seems like a lot...



I'm looking for solutions to my issue here, not worrying about my post count. Thank you for the help though.
 
Tale it apart. Clean the bolts,holes and both mating surfaces. Put a layer of mega grey or ultra black on the housing
No gasket.

Put teflon thread sealer on the bolt threads.

Put it together and run the bolts down with a socket and extension only.

Wait 30 minutes then snug the bolts down. Walk away for a few hours then refill the system.
 
Multiple threads about the same problem is really bad ettiquitte. Find the old thread and post new information to it. That way the readers have the back-story of what was done so far.
 
Dont use RTV on the bolts. On a 350, make sure both sides are flat and clean, manifold and housing. Apply teflon thread sealant to the bolts and use high tack gasket sealant on both sides of a felpro paper gasket.
 
Originally Posted by mk378
Multiple threads about the same problem is really bad ettiquitte. Find the old thread and post new information to it. That way the readers have the back-story of what was done so far.

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Originally Posted by Timmastertech
Dont use RTV on the bolts. On a 350, make sure both sides are flat and clean, manifold and housing. Apply teflon thread sealant to the bolts and use high tack gasket sealant on both sides of a felpro paper gasket.



Like liquid Teflon thread sealant or can I use Teflon tape?
 
If it is the style of thermostat that is supposed to have the rubber gasket around the flange of the thermostat make sure that it is there. Some parts places will sell you a paper gasket that will leak instead of the right gasket.
 
Originally Posted by jhellwig
If it is the style of thermostat that is supposed to have the rubber gasket around the flange of the thermostat make sure that it is there. Some parts places will sell you a paper gasket that will leak instead of the right gasket.


How do you know if it needs a gasket around the outside of the thermostat?
 
Originally Posted by Timmastertech
Dont use RTV on the bolts. On a 350, make sure both sides are flat and clean, manifold and housing. Apply teflon thread sealant to the bolts and use high tack gasket sealant on both sides of a felpro paper gasket.

This is exactly what I would recommend as well.
 
If Teflon sealant compatible with antifreeze? I worry about that stuff getting in and clogging stuff up.
 
Originally Posted by Chris142
Tale it apart. Clean the bolts,holes and both mating surfaces. Put a layer of mega grey or ultra black on the housing
No gasket.

Put teflon thread sealer on the bolt threads.

Put it together and run the bolts down with a socket and extension only.

Wait 30 minutes then snug the bolts down. Walk away for a few hours then refill the system.


This....Chris142 does these repairs for a living.
 
So Chris I can use any Teflon thread sealant? I was going to use the high temp thread sealant with ptfe. Is that sufficient? Or should I use the high performance thread sealant good for 10,000 psi. I don't see a heat rating for that.
 
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