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.

[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
Posted via Mobile Device

[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.

[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.

[tucsonjwt]

I picked up a new fail safe thermostat so I will see if that affects the temp gauge at all. I would think that the current thermostat is opening since the temperature is reading lower than expected on the gauge. Or, I could have a bad temp sensor.

[tucsonjwt]

So...

Installed 180 degree fail safe thermostat

Applied 1/8" bead of Right Stuff to intake manifold contact surface

Installed thermostat housing with factory bolts, coated with Permatex white teflon paste and torqued to 30 ft/lbs.

Waited two days without starting the truck.

Added coolant to top off radiator

Drove truck for about 5 miles - up to 55 mph

No leaks visible from thermostat housing

The sealant oozed out a lot around the base of the thermostat housing (I hope it did not ooze too much on to the thermostat inside the housing) but I don't want to trim the excess away and risk damaging the seal.

Temperature gauge registers as before at about 160-165 degrees. Ambient temperature is now about 92 degrees and 33% humidity ( monsoon conditions, might as well be in the Midwest).

I pointed my mini infrared thermometer at the thermostat housing (about 1 inch away) and it registered about 183 degrees with the engine running.

I guess the temp sensor measures coolant temperature, not actually engine temperature (which is much higher). I do have a factory oil cooler so that may be cooling the engine down a bit more than would normally be the case. Still, that big block always throws off a lot of heat when you open the hood after it has been running awhile.

My fingers are crossed.

[TrailerTrash]

i had a similar problem with a thermostat housing that wouldnt seal. it wasnt untill i used a straight end on the flange that i discovered the problem. it was warped just enough to not seal but not enough that i could really see it without the edge.

just saying it could be the thermostat housing itself

[tucsonjwt]

The thermostat housing looked flat. It is an aftermarket aluminum one from NAPA - I think Four Seasons makes all of the aftermarket ones. I am sure that over torquing one side would cause a warp. The pitting and porosity on both manifold and housing was very bad, so I am thinking that was the issue (I hope.) That Right Stuff is very thick, so that alone might have done the job, even with surface issues. Time will tell.