Thermostat Housing

ok I have had two xj's that have had cooling issues first was a 93 the second one is a 91. after changing the thermostat on both of em I have had issue with the thermostat housing sealing to the block on both xj's. the engine is the H.O. 4.0. does anyone have any tricks to get it to seal?

you put the thermostat and seal on in the right order right? There is a recess in the block to set the thermostat into. It it fell down and or out of that recess it will not let it seal. Are you using the seal/gasket and rtv? Just rtv? Just the seal/gasket?

I usually put a little rtv in that recess and then set the t-stat in it first then use a light(skim) coat of rtv on the t-stat gasket ton both sides. Do the side that goes onto the t-stat housing then stick it to it then the other side and let it sit for a couple minutes. Then bolt it up. Never had any issues doing it that way. When I say "skim" coat I am talking just that , a very thin layer.

I had an issue where fluid was seeping out and not allowing the RTV to cure and causing a leak. I replaced the housing and used RTV with a gasket and allowed it to cure over night without filling the cooling system. However, the small amount of coolant that was trapped in the head was seeping out some how. I was able to see the paper gasket was wet right along the bottom and the RTV was washed away.

I now use a couple paper towels to soak up as much of the coolant in the head through the thermostat opening as I can, haven't had an issue since.

thanks for the input im still working on the coolant system on the xj I have now currently I do not have the t-stat install im still troubleshooting the system no t-stat is only temporary after I insure my system is good to go i will reinstall it.

When I change out a T-Stat on the Heeps, I literally pull out as much coolant as I can from the head. I reach in and scoop it out. I will also use a shop rag to pull out the coolant. The coolant must be well below the T-Stat opening to insure a dry mounting point. Once it is completely dry, the sealant will do its job. Give is time to cure before subjecting it to either heat or coolant.

Just my .02...

I battled this for about a year with three new housings. Come to find out it's all about the orientation of the thermostat. You can do everything right but if the orientation is wrong it will leak.

If the thermostat is not properly oriented the the bar that goes across the top of the thermostat will make contact with the housing and prevent the housing from fully sealing against the head.

1. Hold the housing in your hand.

2. Place the thermostat on the housing.

3. Slowly rotate the thermostat as it sits in the housing and look closely. As you rotate it you will see that at certain points the thermostat makes contact with the housing and slightly pushes itself out of the housing.

4. Note when the thermostat sits flush and mount it in that orientation.

Also make sure the housing is flat.

Run a file across the housing to make sure it isn't warped (or even better, do some figure 8's on a non-moving belt sander to make sure the housing isn't warped.

Thanks for helpful tips when im done ill post how it goes

Nowadays I like to use indian head gasket shellac with the paper gasket for this job. It is tackier than RTV right out of the bottle, which makes it easier to keep everything lined up. Cleans up right away with acetone, no scraping or scrubbing.

I put a little bit around the inside of the lip on the Tstat, and set it in place. I'm pretty sure I always orient it so that the "bar" on the face is horizontal (and so that the hole I drilled in the flange is at 12 o'clock). Paint both sides of the paper gasket with the shellac and let that sit for 15 minutes or so. Stick it to the cleaned surface of the housing using the two mounting bolts to line it up. Place the housing, gasket, and bolts into position as an assembly, then fiddle with getting the bolts started, and snug them down.

Do you have much pitting on the gasket surfaces on the housing or the head? The aluminum-iron interaction can cause pitting- in my case the iron head has taken the worst of it. Still never had trouble with it leaking, but I doubt I could get by without using a gasket like some people do. I've thought about filling the pits with JB Weld, but won't bother until I can't get it to seal anymore.

If you use RTV, make sure you let it set-up (skim over) before installing the housing, and then only snug the bolts to finger tight. Let that sit about an hour and then snug the bolts up the rest of the way. You want to let it harden some before clamping down on it, else you will squeeze all of it out.

Also, as with most gaskets, tighten the bolts incrementally. Don't torque one all the way down and then do the other.

Well after a new raditator I think I have solved my overheating issues. I used a wire brush wheel, carburator cleaner, and a scotch brite pad to clean the thermostat housing and block. To seal the gasket I used a small amout of rtv to hold the t-stat seated in the block, I took the gasket and put a thin glaze on the block side of the gasket and placed the gasket on the block, I let rtv set up for about 30mins or so, I took the housing and put a thin glaze on it before placing on the block I snug the bolts up just hand tight and let rtv set up another 30min before torqing the bolts down. I waited about four or five hours before puting water in the system I dont see any signs leaks and it maintaing 210 no problem thanks for the tips.:sunshine: