Thermostat Leak - Need Advice Please!
 

I've had a minor leak around the thermostat housing on my Roush 402 on & off for 2-3 years. There was a tiny leak this year which I decided to try to fix once and for all (I should have left it alone). :rolleyes:

New gaskets. Leaked worse. New gaskets and gasket sealant. Looked like Bellagio fountains!

So I took my billet spacer (which was pitted a bit) and my chrome thermostat housing to a machine shop and they put them on a very flat table. The spacer was flat but the housing wobbled and definitely was the problem (I probably overtightened it in frustration). He said to just to just sand the spacer with a sanding block or on a flat surface to clean it up.

So I layed some sandpaper face up on my granite countertop and sanded the billet spacer and it cleaned up fairly good and it felt pretty smooth. I got some new felpro gaskets, new thermostat and a new aluminum t-housing from Napa.

I put it all back together, torqued the new stainless steel bolts to 15lbs. and of course it leaked. Without even starting the engine it dripped out pretty good between the housing and the spacer at the bottom.

Took it back apart and this time I added gasket sealant to the new gaskets and bolted the spacer and t housing together and let it sit for 1/2 hour to set. I then put a new gasket with sealant on both sides on the block side of the spacer and put everything back together. Leak was worse than ever, same spot.

HELP!! :mad:

Normally, it's a pretty easy job to switch out a thermostat and not have a puddle on the floor when you start her up... but you know that. I would guess that either that chrome thermostat housing or the flange that it mounts to is warped. Pick up a new housing off of Ebay, even if you don't like the way it looks, and see if you can get it to hold with a new housing. If that leaks just as bad, then I would guess the flange that it mates to is warped or cracked.

Everything is brand new except for the billet spacer. The leak is coming from between the new housing and the spacer. The spacer doesn’t appear to have any cracks in it.

Flat surfaces on housings, completely clean and dry, 1.5mm bead of RTV on both sides of each gasket, let set 10 minutes, assemble, torque bolts to 10lbft, LEAVE OVERNIGHT, refill with water first, water is cheap, all ok, drain out, and refill coolant, bleed system etc.

I have had some trouble with spacers not being completely flat. Clean everything off very well, wipe it dry with alcohol or some non greasy cleaning agent and then put it on a completely flat surface and see if you can see any deviation at all in the area where the leak is. I used a wire brush to clean mine and there was a very tiny, almost impossible to see place that wasn't flat. But I made up for this as mine had an O ring groove so I used a slightly oversize O ring and gaskets which I put some sealer on and let set for a minute or so then put everything back on and torqued it down. I never had so much as a drip after that.

Ron

I know, but that doesn't mean it's any good.:cool: If everything is clean, plumb, flat, and not cracked then you can usually just use a homemade gasket, and tighten it down with a wrench and you're good to go. Try doing what Gaz wrote and, if that fails, then something is either warped or cracked, even if you think it isn't. That's the only possible answer.

When I want a leak free assembly, I use Indian Head gasket cement, done!

I never use RTV. I use 3M General Trim Adhesive. Spray it on the housing, put on the gasket, let dry for about an hour, and bolt it together. I have been using it for 30 years on everything from oil pans and transmission gaskets to water pump and yes, thermostat housings.

https://www.amazon.com/3M-08088-Gene...+trim+adhesive

The problem is the housing. You said it wobbled on the flat plate.
Why didn’t you have the machine shop mill it flat.
Anyway, I had same issue with chrome housings, it can’t tell you how many I returned.
I finally painted the old cast housing blue and it has not leaked in 15 years using only the standard paper gasket and a bit of sealant.

I'm leaning on the strong possibility of a hairline crack in the housing which widens when heated.

While the last two answers likely summarize the help needed, here's a longshot just in case. Is one of the bolts bottoming out before fully sealing with intended torque. Aain, I wouldn't think that's it because that would seem to leak at both layers. Also, you'd likely notice that. And, also, if it was it could be due to uneven casting as mentioned above and may then be part of a joint solution of milling and right length bolt.

Best of luck! Brent

Like Ron61 said. Grooves and O-rings. And then a little sealant does the trick.

Cheers
Greg

You are not using one of those Mr. Gasket chrome thermo housings are you? I remember hearing horror stories from people about them.
You said in one of your repair attempt descriptions that it leaked even without starting the engine.... so system was not hot or pressurized and still dripped....
I'm liking the long bolt possibility scenario... you could remove the housing and just replace the bolt to see how far it threads into the manifold as a quick check. Not the issue if it bottoms out or the bottom of the bolt head is visually lower the thermo housing flange thickness. Could also go with stud and nut to replace bolts. where exactly id the leak emulating from? Grab a cheapie replacement housing from an autoparts store and fit it to see if the problem persists.
Blas

Here's another longshot just in case! Any chance the thermostat is upside down and of a design that such is not allowing full seating when torqued down?

Brent

The old t-housing was a Mr. Gasket I'm pretty sure and it was warped. I now have a new t-housing from Napa W2486 and it seems like a good one. No wobble but the jury is still out until I fix this leak. Bolts are brand new stainless steel and they aren't bottoming out and I'm using new S/S washers. Thermostat was put in last time correctly and I used some gasket sealant along with new FelPro gaskets and let it set for 1/2 hour.
Both times when I tried gasket sealant it leaked more and the last 3-4 attempts it leaked without engine running - no pressure.
At some point tomorrow I'll try again without a thermostat (just in case it moved) and if it still leaks then I'll try Gaz64's suggestion. If that doesn't work then I'll take the spacer back to the machine shop to make it perfect and start over. (grrr) lol

I'll double check the bolt lengths tomorrow too. One's 3.5" and the other is 3". I imagine I could shorten them a touch to eliminate that possibility.

Go to a Ford dealer parts department and buy the sealant used on diesel trucks. It is grey and pricey but it works. The stock thermostat housing works best.

I had to Dremel out the aluminum superformance spacer a bit (taper the inner shoulder) to ensure that the Tstat fit in there dead flush...checking without the Tstat would tell, but so would just fitting it and placing on a flat surface...I've fallen prey to the too long bolt scenario too, but you may take a look and make sure your Tstat is fitting all the way flush...

Fully threaded bolts or with an unthreaded shank.... just covering all the bases here.
Blas

Unthreaded shank