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Thermostat keeps leaking, help please!

H

hopper720

NAXJA Forum User
Location
Connecticut
Long Story Short:

Changed thermostat and housing and it leaked. Replaced with new gasket and silicone now to fill the potential leak areas and...leaked. Did it one more time just for ha-has with new gasket and silicone and it was fine...then once i started driving it leaked.

Its leaking right by the bottom bolt. I have no idea what to do.

Any ideas?
 
My technique is this. Lightly silicon the gasket, stick it in place. Lightly bolt the thermostat housing in place - just barely tighten the bolts. Wait a few hours for the silicon to setup some, them tighten the bolts. Wait a while longer before refilling with antifreeze. Also make sure the thermostat is seated corrected and not installed backwards.
 
ALL good advice.

It doesn't take much of a piece of old gasket/sealant left on a surface to cause a problem.

I'm old school on t/stat housings. Clean both surfaces with a wire wheel, use your fingernail to check for irregularities. Occasionally the area around the threaded bolt holes become "raised" and must be dressed down with a file.

I use Permatex non-hardening sealer. I apply it sparingly to the recess in the t/stat housing for the thermostat flange, and then to the t/stat housing gasket surface--this will hold the thermostat in place along with the gasket. I don't use any sealer on the engine side--makes cleanup easier next time. Stick the bolts into the t/stat housing holes and carefully set it in place, holding it firmly against the engine, run the bolts down finger tight, then use a socket/wrench and alternate turning each bolt until down tight.

Good luck.
 
I to clean the surfaces, both on the block and on the housing, then I coat the new gasket with Indian Head gasket cement, brown gooey stuff, put it on the housing and let it dry for a while, put the thermostat in and then put it all together, start it up. Oh, torque the thing down too, by the book, I'm not a fan of that feels about right. I also usually put some indian head on the bolts too.
 
joe_peters said:
Occasionally the area around the threaded bolt holes become "raised" and must be dressed down with a file.
Click to expand...

Oooh, another good one. Put a piece of aluminum oxide sandpaper on a flat surface and run the tstat housing around on it a few times. That will show you any high spots and you will know when it is totally flat.
 
Go really thin with the silicone on the gasket. Too much tends to make mine leak.
 
The gasket for my water pump was leaking out of the top, and I thought it was the thermostat's gasket, it was kinda hard to tell...Prob not your issue but Just a thought.
 
While apart AND with thourghly cleaned engine/housing.

Take the thermostat HOUSING ONLY (NO GASKET, SEALER OR "STAT.)and test fit it to engine.
With the bolts just snug down lightly there should be no gaps and housing firm against engine all around. Bolts should both be holding housing. If one is Not, swap bolt locations as one may be longer.

Keep bolts identified which goes where.

If all is OK, then continue as above on installing the 'stat and gasket.

Good Luck,
Orange
 
Did it leak before you took it apart?
 
So even us old experienced guys aren't impervious to this. Changed did a system flush and changed my tstat over the weekend (inability to heat up told me it was stuck open). Old housing was installed with a lot of silicone. Cleaned it up and ran it over some sandpaper and it was definitely twisted. Should have known better right there...all the little voices in my head...but no, I just spray some coppercoat on the gasket and reinstall it all. It leaked. $14.99 for a new housing from Napa and $0.99 for new gasket and it is all better now.
 
Replaced tstat for the fun of it when I was doing my radiator. Now I've got steam coming out, was fine before. I've done two in the past, no gasket sealer and had zero problems.

If it is cracked would you be able to see it? Hard to get a good view on it with the little hose still on, I guess I should take that off so I can turn it all the way around.

Any one know the foot pound torque spec on the bolts?

Debating pulling it apart on putting sealant on, if I go to that extent I should probably buy a new gasket yes? Maybe I crushed the gasket it torquing too hard?

I thought I had it clean, used a razor blade scraper to clean the engine side, the housing side seemed clean. Could I have scratched the engine with the razor enough to cause a leak?
 
I'd pull it back off and have a look. See if you see a crack (may only be a hairline one and hard to see). If it were me, I'd go ahead and replace the gasket again just to be safe...since it's only $1. I've always used goo in addition to the regular gasket. The hi-temp RTV (red in color) has been working quite well for me.
 
Well, they're $4 not $1, maybe you're getting them wholesale...Not that $4 is going to make me lose my mortgage, but heck man, that's a burrito! :)

So anyway, yeah bought a new filter. Cleaned up the mating surfaces super well. Let it get completely dry. I added a tiny smear, not a bead, of RTV to fill any potential scratches or imperfections. Put it together, Let it sit dry overnight. Added fluid this morning and started dripping immediately before even pressurizing the system.

I think I could have possibly gotten a tiny spot of grease on the filter as the tstat kept popping out of place as I was trying to put it together.

Wondering if that is true, if the grease might deplete itself and then stop leaking? Also wondering if the gasket might expand now that it's wet and fill any imperfections? It was dark again by the time I was getting it back together so I did not use a straight edge. I did look at it really close and did not see anything resembling a crack...

Pretty crazy when I did one a few months back it took me about 5 minutes and had zero problems...
 
hopper720 said:
Long Story Short:

Changed thermostat and housing and it leaked. Replaced with new gasket and silicone now to fill the potential leak areas and...leaked. Did it one more time just for ha-has with new gasket and silicone and it was fine...then once i started driving it leaked.

Its leaking right by the bottom bolt. I have no idea what to do.

Any ideas?
Click to expand...

The factory thermo housing has a tendency to develop a hairline crack due to the poor casting. I've seen it on numerous 4.0s, and even on our rig. Dorman makes a replacement for cheap (under $8 bucks).
 
Filter????????????????????????

Are you installing the T-stat upside down?

Have you cleaned out the inset grove the T-stat lays in first?
 
$4 for a thermostat housing gasket? Where are you buying them??? Everyone i've ever bought has been a buck.

Either way, at least you got it fixed.
 
Boostworks - thanks, I guess if it is still leaking tomorrow I will get a new housing. Now that I am searching around regarding new housings I see "high flow" housings. Necessary or effective?

Ecomike - don't know what you mean by filter, I did use a felpro gasket. Previously with no RTV and no problem. This time, once dry and once with RTV. Tstat not upside down, or backwards, and yes, cleaned very well.

UNCC, I've called the 4 main chains, and that is the going rate at all of them. Not fixed yet, unless I go out tomorrow and hopefully the gasket has swelled under moisture....


Edit, okay well I changed my search parameters and now I see there's a dozen threads on thermostat housing, it was a lot harder to search without the word housing...Was in a hurry before, guess I'll read up.
 
Last edited:
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