Leaky thermostat housing

Sierra Cam

Sierra Cam

New Member
Joined
Dec 28, 2018
Messages
23
Location
Foresthill, Calif.
Hi All!
have only owned my TJ for 6 months and when I first got it, found that not only did it have the wrong antifreeze, but the thermostat housing was leaking as well. so I took it all apart, flushed the motor (4.0 I6) and installed a new pump, thermostat housing and hoses.
To my chagrin, when I pressure tested it, I found that i could not get the thermostat housing to seal against the head without shimming with a very thin piece of gasket material on the side that looks to be a bypass cavity.
the surfaces were cleaned thoroughly and i was using new gaskets as well as RTV but could not stop the leak until i added the extra gasket material.
anyone else have this problem?
 
Did you inspect the mounting surface properly? Did it have any fine grooves or wear marks on it?
 
No, all looked well... I cleaned it thoroughly and didn't see anything out of the ordinary. I've done quite a few of these over the years on other vehicles I've owned and this is the first time I've had so much trouble getting it to seal.
I went through 3 different gaskets and finally "shimmed" it with a (I hate to admit) piece of newspaper.
It's on there dry, and because of the questionable material I used, I watch it very closely.
So far, after three months, it's still holding - just don't know how long my makeshift gasket will hold which is why I'm asking about this now.
 
Most of the times its caused by a spec of dirt or old remaining gasket. When I replaced mine two years ago I spent over an hour carefully cleaning the area with a razor blade.
 
It's possible your leaks are caused by a damaged/warped thermostat housing if not small barely perceptible bits of the old gasket left behind. It WILL leak if the gasket seating surfaces are not absolutely 100% pristine and free of bits of the old gasket material. If the gasket surfaces are absolutely bright and shiny 100% clean and it still ends up leaking, thermostat housings are inexpensive, I'd try replacing it together with a fresh gasket. Don't use RTV anywhere in the cooling system.

I had a makeshift gasket cut out of an old MRE cardboard box during an emergency trail-fix that was leak-free for 6 weeks until I was able to get the time to replace it with an actual gasket. I just made sure to wire brush the gasket seating surfaces with a small wire brush so it was perfectly smooth and clean before putting it back together with the makeshift gasket.
 
it leaked even with a new thermostat housing which is what has me totally baffled!
After reading some of the threads on this site, i'm thinking there may be a couple things I did that may have contributed to my problem...
#1, over torquing... i didn't use a torque wrench, just a 3/8" socket and ratchet and according to what i've read, these thermostat housings are very sensitive to the amount of torque used. like i said, i've done a number of these and snuging the bolts "firmly" has always produced a leak free repair.
#2, going back to what you mentioned about a really clean sealing surface, I used a 3M scotch brite pad on an angle die grinder at low speed to remove the old gasket and anything else on the head that might have interfered with the sealing of the housing. Done this many times with good results.
i have to say though, that in thinking back, i do seem to remember a darker area on the head sealing surface in the area that was leaking.
perhaps i just answered my own question?
the old housing had been leaking for some time and was corroded not only on the neck where the rad hose attached, but also in the area that matched the dark area on the head which is why I replaced it.
that being said, could it be the head has lost it's flatness in that area due to corrosion? that's hard to believe... or, has anyone heard of new thermostat housings being so poorly machined that their gasket surfaces are not flat?
 
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