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Question: Thermostat housing leak.

3XBLACK67

Active member
Joined
Apr 29, 2004
Messages
36
Location
Milwaukee, WI
Corvette
1967 triple black 390 HP roadster
A small amount of anti-freeze leaks from the bottom of the thermostat housing on my 427/390, where the housing joins the intake manifold. I have tried different gaskets and stop leak products with no luck. Today I took the housing to a shop to have it machined flat, in case it had warped a bit. While getting it ready to re-install, I noticed that in one of the two bolt holes, there is a rubber plug with threads for the bolt. The rubber looks like it has disintegrated a bit. Could this be the cause of the leak? If so, can the rubber piece be replaced? I don't want to replace the housing with a new one because this one appears to be original, with the GM logo and correct part number at its base.
 
That 's weird

Sure it's not black silicone ?
can you post a pix ?
 
Thermostat housing leak

Sure it's not black silicone ?
can you post a pix ?
The only digital camera I have is a point and shoot that won't clearly focus on such a small object. I do think there is a piece of rubber with thread marks in the bolt hole that holds a long bolt, but that can't have anything to do with the leak because the bolt holes are outside the area where the anti-freeze passes through the thermostat housing. I will try again now that the face of the housing has been machined. I think that I have a very good gasket. It has a bead of semi-pliable silicone on both sides. Do you think that it is best to use a sealant as well, and if so, what kind? I went to the local parts store today, and found that I had a wall of sealants to choose from. I choked, and walked out without having bought any! How do you know when you have the housing bolted down tight enough? I don't want to crack or warp it, but obviously want it tight enough to do the job.
 
I like permatex blue for coolant

Using one hand on 3/8 ratchet should suffice.... You do not need a hugh amount of torque to hold it down...
You just need flat CLEAN surfaces and a good gasket...It's only 15 PSI it needs to hold from leaking.
 
You can use head bolt sealer, it works great for sealing any threads.
 
With the bead of silicone built into the gasket and clean flat surfaces you should not need any other sealant. Be careful not to over compress the bead. Torque to 30 lb. ft.

Tom
 

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