Sealing the thermostat housing

[tucsonjwt]

The thermostat housing (aka water outlet) is leaking again on my 83 c20 454 BB. I replaced it a few years ago and had to reinstall it twice, using a lot of sealant, in order to stop the leaking around the gasket.

I have read a lot of opinions (use the o ring type of outlet with no sealant, use RTV and no gasket, don't use RTV, use the Right Stuff...)

Does anybody have any advice on my next attempt to seal this thing up?

My current replacement looks like cast metal - I think I got it from NAPA.

Thanks.

[Justins76]

I always use the fel pro Permadry plus gasket. Its like $10 but reusable. Dont use any sealant.

[tucsonjwt]

I am thinking that there is some porosity and/or unevenness in the mating surfaces which is causing the leak. So, I think I need something to compensate for the imperfections - filling the gaps - so I am not sure that just a gasket would work. I think an upgraded Fel Pro gasket is what I eventually used, but that leaked and I added a sealant (blue, I think) which lasted a couple of years.

[Titomars]

Originally Posted by justins76

i always use the fel pro permadry plus gasket. Its like $10 but reusable. Dont use any sealant.

x2

[Pine Bark Auto]

A less expensive alternative may be the current GM replacement gasket. It has a bead of silicone sealant of some sort on each side and I have never had one leak. If your manifold is extremely pitted, I would suggest the sealer BLT suggested. If the water outlet is pitted, just replace it. Depth of bolt holes would be worth checking to make sure you are getting good clamping on the gasket. Look at the length of the bolts vs the thickness of the housing vs the depth of the holes. Chip.

[Ziegelsteinfaust]

Have you sanded done te base of the t stat housing, and manifold.

[Jonlopes]

I hate Silicone gasket sealer. I use a old fashioned paper gasket with Permatex Non-hardening on both sides. I have never had a leak yet.

[tucsonjwt]

I never had a leak with a paper gasket until this experience with the BB.

I did sand and clean both intake manifold and thermostat surfaces prior to installation. (As I recall, I did 4 separate installations using various methods before I used the blue goop.)

I would like to avoid goops and gunks but I have not heard of any alternatives that would work in my situation - dry and sealant applied to dry gasket did not work. I think the inherent surface condition of the intake manifold and water outlet have some issues.

[raceman6135]

I had an intake manifold where one of the thermostat housing bolt holes was not tapped quite as deep as the other. When installed, the bolt in that hole bottomed out ever so slightly -- only enough that after a while, it began to leak.

Instead of risking possible damage to the existing threads by drilling and tapping deeper, I simply put a couple of washers under the bolt head. Problem solved.

[BLT gmc]

The Right Stuff from NAPA is a pematex product that will seal all the imprefections you are suspicious of. It is not silicone! It is the best I have ever come across. Not paper or gasket needed. We use it in OTR trucks, axles, rear-ends, trans, etc
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[Dead Parrot]

I use a cast iron housing, Felpro gasket and aluminum intake. Sanded the housing to flatten the casting flaws. No sealant. No leaks after a few thermostat changes.

One thought on the bolt holes. Make sure an accumulation of dead sealant hasn't partially filled the holes.

[tucsonjwt]

I spent about 4 hours this morning sanding off the intake manifold boss and the bottom of the thermostat housing. There was lots of pitting/porosity on the intake manifold - I think this was caused by the original cast iron housing which rusted through the gasket and accelerated the manifold pitting.

I cleaned out the bolt holes in the manifold. These are blind holes which are enclosed by bosses which molded to the underside of the intake. One of the bolts was very rusty, so I wonder if there is a pinhole leak in that boss from the underside? I made sure that the mounting bolts are now cleaned off and threaded them far enough into the manifold to insure that they will seat all the way when the housing is installed.

I poured some water into the upturned housing to check for leaks from the TVS switch and the threaded plug in the top. No pressure using this method, but no leaks detected. I did not notice any coolant coming from the top of the housing. However, the problem with coolant leaks is that they are usually not detectable on top of the intake manifold because the hot engine burns off any coolant that leaks.

So, what should I use as a thread sealant on the mounting bolts? Teflon paste or tape? Nothing?

I am leaning toward the Right Stuff, given the repeated leak history on this truck.

One interesting side note, the thermostat in it now is 180 degrees, but the temp gauge in the truck never shows over 165 degrees. I guess my gauge most be inaccurate.

[BLT gmc]

I would use the teflon paste/liquid on the threads and the Right Stuff on the mating surface. Since this has been an area of repeat problems I would let the Right Stuff cure well before applying coolant and radiator pressure. Good Luck, Keep us posted, Bruce

[tucsonjwt]

Looks like the right stuff for the gasket, ptfe paste for the mounting bolts, and another 180 degree thermostat. Thanks for the input.

[Dead Parrot]

Since getting a good seal has been a challenge, while you have the thermostat out, might put it in a pan of water with a meat thermometer, heat the water up and see if the thermostat is opening when it is supposed to.

Easier now then after you get everything nice and leak free then start wondering if the temp gauge or thermostat is off.