View Full Version : tstat housing gasket?

09-19-2013, 08:26 PM
So I picked up 3 felpro gaskets and they has some girth to it. But failed to seal. I picked up a victor reinz one and its pretty thin. Is this thin gasket going to seal better, does a thicker gasket distort the housing? Just curious about what we should be using to not ruin tstat housings.

09-19-2013, 08:37 PM
Felpros have worked well for me - 4 months and no leaks. Loctite 'Superflex' Blue RTV silicone. Let it sit installed overnight before adding coolant and running engine.

No experience w/other brands, sorry.

09-19-2013, 10:33 PM
I used a Felpro gasket and orange rtv, I've had it on for many many years with no problem.

09-19-2013, 11:04 PM
Felpro and ultra black RTV on the thermostat housing side only has worked well for me. I let the RTV cure for only about 30 minutes before installing thermostat housing and tightening the bolts, then leave it to cure overnight before filling it up with coolant.

09-20-2013, 09:44 AM
You may have heard this all before but I'm going to type it out for the newbs and it may remind you.

#1 - The thermostat housing is a pain in the arse because it only has two hold downs for the large area and it is made from stamped steel. This means that if you over torque the bolts, you'll warp the mating service of the housing. In fast the surface may warp over time just from the right torque and heat. Thus when you take it off to replace the thermostat and put it back on it won't seal.

#2 - The intake manifold is cast aluminum and has porosity. I've seen poor quality surfaces on the intake manifold and it too could be warped, but usually it isn't.

#3 - You must make the mating surface of the thermostat housing flat before putting it back on. You need a sheet of 400 grit sand paper or sheet of emory cloth on a flat concrete floor or flat bench top. Then slide the mating surface of the thermostat housing over that sand paper using even pressure. Do a few swipes and take a look. You'll notice where the high and low spots are. Keep doing that until you have no high or low spots. Clean the surface up with a finer sandpaper or emery cloth. Wash everything well after this.

#4 - If the manifold surface has porosity or is uneven I spread some RTV (for coolant, so blue or orange) on the manifold and then stick the gasket to it and let it get tacky.

#5 - I tack the thermostat to the housing by using super glue on a couple spots. Then carefully position the housing onto the manifold avoiding the gasket.

#6 - tighten down the mounting bolts only until a little pressure is felt. Then tighten them both down evenly to around 12inch lbs. It's not very much, you don't' want to force any rtv out all over the place and you don't want to warp the housing.

#7 - Let it sit over night so the RTV can cure. Check the bolts in the morning to make sure they are still tight.

Some other observations:

Felpro started making thermostat gaskets with an elastomer ring around them that solves this problem completely (assuming you don't over torque), unfortunately they don't make such a unit for our application.

Permatex makes a product called Right Stuff Gasket Maker which is essentially a two part elastomer product that comes out soft stays pliable, but sticky and can be used as a gasket replacement. I used it on a perpetually leaking AOD transmission pan and it hasn't leaked a drop since (I spent hundreds before that stuff with new gaskets, and various attempts). If I was serious I'd try it on the thermostat housing. Only downside is the stuff is a pain to clean off. It's tough stuff.

09-20-2013, 11:10 AM
This is the only thing to use! I've had two different t stat housing off,planed,and back on so many times, I can do it blindfolded and drunk, while sleeping! :D I used a standard felpro gasket with the "right stuff" applied to housing and intake. Have had no leaks since. That was 3 years ago. Also used it on sc hat. I only have it about 1/2 torque and let it sit over night before giving full torque to prevent squeeze out.

Permatex makes a product called Right Stuff Gasket Maker which is essentially a two part elastomer product that comes out soft stays pliable, but sticky and can be used as a gasket replacement.[/QUOTE]

09-20-2013, 04:09 PM
If I'm not mistaken, make sure its the correct t-stat. It should twist and lock into the housing. Gasket thickness should not matter.

09-20-2013, 05:56 PM
I run the housing on a belt sander prior to.

Never had an issue.


09-20-2013, 06:42 PM
Thanks Mike and others, and thanks for the tips on installation.

You guys are missing the original point. I know the housing is stamped steel and that is weak, but is a thicker gasket that compresses on the outer edges and not so much on the center due to the way we are applying force, is that a good reason why we are trashing these things on the regular? Will the thinner gasket allow the flange edges to bottom out on the alum housing before warping while allowing the center to seal up well?

Its easier to compress the gasket at the outer portions and maybe over torqueing on the bolts easy to do with the thicker gasket.

I don't remember what the ford gasket looks like.

09-20-2013, 06:58 PM
I doubt that gasket thickness between the two examples is a factor when it comes to any distortion that you might be seeing.

09-20-2013, 07:45 PM
I have also noticed that on corroded hose necks its a hard to slip on the hose, and seems that I'm putting excessive force to the flange area by turning the rad and tugging the neck like a lever, I guess with enough leverage it can pull on it and ruin it. Something I must consider when I go installing the new one that's arriving.

I guess my intent is to compile information that might be useful in preventing the damage of a good t-stat housing.

09-20-2013, 07:58 PM
I was disassembling a housing recently, and had to clamp the base in a vise to hold it while I tried to remove the sender. I put a wrench on the sender _only_ and promptly twisted the standoff _and_ warped the base at the same time…ouch.

The standoff/boss for the sender has it's own wrenching surface (just like the air bleed w/skirt). Using two wrenches, instead of just one on the sender, removal worked as it should without further deforming the base. Now I know - the base seems to warp easier than I would have guessed.

I used a wrench on the boss to take the warp out of the housing base, checking with a straight edge, then finally wet sanding to dress it out for the gasket.

I also use RTV on the bolts when installing.

As for twisting the outlet to the upper hose, I think that may also be a risk when using a 3-jaw puller on the sc pulley. I'd guess small amounts wouldn't create a leak on an installed housing, but who knows case-by-case.

09-20-2013, 09:04 PM
I've not found the manifold to move too much warpage wise.

Belt sand the T Housing. I want it to shine.

Thin coat copper RTV both sides of gasket. (just barely seeps to outside edge) Don't care who's gasket it is.

Treat the hose ends the same as soldering copper pipe.

Little spit on the paper and sand them down.

I put a thin coat of lithium grease on the housing and it seems to slip on and load up pretty tight. This also makes it a no brainer when removing and may go a long way to back filling the raw housing pores under the clamp.

Turn TH bolts to snug and give them a small push. (1/16)

Let sit for half hr.


sam jones
09-21-2013, 12:54 AM
Good evening

I have had good success installing the thermostat housing/gasket by doing the following:

1. Checking the flange with a straightedge. Adjust as necessary.
2. Remove the remains of the gasket, clean and sand (220 grit) both intake manifold to thermostat port and the thermostat housing.
3. Use the correct size tap and chase the intake manifold to thermostat house threads. You will be surprised how much "junk" is removed.
4. Prior to installation apply a small amount of anti-seize to the thermostat housing bolts.
5. Recommend using Permatex Ultra Black RTV on both sides of the thermostat housing gasket sealant.
6. Install thermostat housing, thermostat and gasket to intake manifold. Torque bolts. Wait 15 minutes. Recheck torque. Repeat as necessary.

Good luck.

09-21-2013, 05:09 PM
Reading all these posts....I'm sure mine will leak during the first start up, but we'll see.

No gasket used only gray permatex sealer to manifold side and sealer on thermostat housing...been on drying for 5 days now. Put more sealer around the outside edges of the two mating surfaces.

09-21-2013, 05:53 PM
Damn my last attempt was to be a successful one. I had bought permatex high tack gasket sealant, the sticky red stuff. I thing it was going to work, since I just removed it all again and the tstat had slipped down on me. I thought I had secured it. But fell down and I tightened it all down. I had a hunch since the top was no longer leaking and only the bottom leaked.

Back to doing it again, I got a new housing, I hope its not damaged.

09-22-2013, 11:54 AM
Success it seems, that permatex tacky stuff and the victor reinz thin gasket and the new to me housing seems to have put an end to my troubles.

Although the temp sender seems to not be calibrated the same as my original. I don't know why I didn't change it over. But got lazy, the fans kicked on at a quarter sweep of the gauge. The old setting used to kick on at the n from norm. Oh well something to do in the future.

Btw My procedure was sand flat the housing, tacky stuff on the gasket and I placed it on the housing working around it gently. Let that dry overnight, next day put the tacky stuff on the opposite side, installed wet. I topped off and ran the car shortly after. No signs of leaks.

09-22-2013, 01:15 PM
Glad to hear everything worked out for you! Now get out there and have some fun with the car!

09-23-2013, 10:26 AM
Glad to hear everything worked out for you! Now get out there and have some fun with the car!


09-26-2013, 01:55 PM
Permatex, "The right stuff" gasket maker. Period, then end. It will account for slight to moderate deviance's in mating surfaces. Apply, half torque till set, full torque and done. Never leak again!