Leaking thermostat housing

[hammer]

I have just put together my 1971 Challenger with a mildly built 340. I replaced the old radiator cap with a new 16lb cap. I am having trouble getting the neck to seal to the intake manifold. I used a quality sealer and gasket but when the system pressurizes, it leaks through the gasket and up the bolts that hold the neck on. Should I go to a lower pound cap? The manual calls for a 16lb cap. Thanks.

 

[moparleo]

Your problem is not the cap. Are you using an original cast iron part or after market pot metal ? An original cast iron part will never leak unless the sealing surface is cracked, rust pitted or extremely warped. Recheck your parts.

 

[challenger6pak]

If it is a chrome aftermarket neck you will have to run an O-ring with it.

 

[hammer]

If it is a chrome aftermarket neck you will have to run an O-ring with it.

Should I be able to pick that o ring up from a local parts house. And yes it is an aftermarket chrome neck.

 

[moparlee]

Your aftermarket chrome neck is not flat. Put it on a known flat surface like a table or piece of glass. I will bet it rocks back and forth. Take it to a machine shop and have them machine it flat.

Not sure about running an o-ring with it unless the surface has a machined groove for the ring. This type can be purchased though.

 

[moparleo]

Easiest solution is to put the proper part on that doesn't need to be machined or o-ringed.

 

[challenger6pak]

Easiest solution is to put the proper part on that doesn't need to be machined or o-ringed.

True.

 

[Chryco Psycho]

Mancini has a billet alum housing for about $20 that work great

 

[hammer]

Thanks for the insight, will pull it off this winter and have the bottom machined flat.

 

[Dodgeboy]

I'm gonna try to revive this thread before starting a new one. My thermostate housing leaks no mater what I do. '71 383, factory w/p housing. My orgjnal thermostat housing was warped, tried to backyard mechanic machine it, fix lasted 2 summers. Bought a new steel 3/8 thick housing ($40us from Mancini) tried every combo of gaskets with/without rtv silicone until I found something that works. Even used wide washers when I bolted it down. Now 2 summers later I noticed its leaking again. Rad cap is newer 16lbs so its not (I believe) over preasuring the system. I didn't notice anything unusual on the w/p housing gasket side. Is there anything I'm overlooking or should be looking at when I pull it off?

 

[bc3j]

I used Right Stuff without a gasket. Seals perfectly. Everything has to be clean and dry. Will be a little tuff to get off. No leaks for me. My cap is 16#. My aftermarket housing turned out not to be flat. Rocked on the housing which was flat. My engine is totally stock components. Switched to my other housing that was a little thicker in the base and the Right Stuff.

 

[Adam]

I like non-hardening “Permatex” on the bolt threads and sealing surfaces.

 

[Dodgeboy]

I can try using a different type of silicone and will check the housing for straightness. I didn't use anything on the bolts. Just won't know till spring if the problems gonna be fixed as winter has just arrived
Thanks guys.

 

[Adam]

I have found silicone tends to peel after a while.

 

[moparlee]

I can try using a different type of silicone and will check the housing for straightness. I didn't use anything on the bolts. Just won't know till spring if the problems gonna be fixed as winter has just arrived
Thanks guys.

My bet is that the T-stat housing is not flat. Take it to a machine shop and have it machined.