Leaking thermostat housing (What am I doing wrong?)

diggerwolf

diggerwolf

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Flushing the coolant system, I first removed the thermostat. Did the Prestone, flushed, then Thermocure and flushed again. Three times I've removed/replaced the thermostat housing and it continues to leak.

1. Didn't use RTV for the flush. Noticed a leak but wasn't concerned since I was going to replace again with a thermostat.

2. Gasket came with adhesive on one side so I used that and a thin line of black RTV on the other side. Leaked bad.

3. Removed and cleaned the housing and tried again with a new gasket and more black RTV. Still leaking.

4. Removed again. Gasket seemed well attached to engine side so I cleaned the housing surface and spread gray thermostat RTV on the mating surface and reinstalled. Waited overnight to refill and it's pouring out the bottom.

Can't really tell where it's coming from, looks to be the bottom bolt.

Help!
 
diggerwolf said:
Flushing the coolant system, I first removed the thermostat. Did the Prestone, flushed, then Thermocure and flushed again. Three times I've removed/replaced the thermostat housing and it continues to leak.

1. Didn't use RTV for the flush. Noticed a leak but wasn't concerned since I was going to replace again with a thermostat.

2. Gasket came with adhesive on one side so I used that and a thin line of black RTV on the other side. Leaked bad.

3. Removed and cleaned the housing and tried again with a new gasket and more black RTV. Still leaking.

4. Removed again. Gasket seemed well attached to engine side so I cleaned the housing surface and spread gray thermostat RTV on the mating surface and reinstalled. Waited overnight to refill and it's pouring out the bottom.

Can't really tell where it's coming from, looks to be the bottom bolt.

Help!
Click to expand...

I’ve been there. Very frustrating. Make sure it’s not the water pump leaking. Get the surface prep perfect. I’ve had very little luck with the gaskets (fel-pro, off brand). I tried with and without permatex RTV. If the thermostat is an off brand it’s surface may not be flush. After 4 gaskets I gave up and bought some of The Right Stuff 1-Minute Gasket Maker (black). Go around each hole and along the mounting surface in a continuous bead (as best you can). Solved. NAPA stocks it.

Don’t forget the hole in the thermostat should be at the top.
 
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I would clean the engine side with a razor blade scraper really good. Maybe housing is warped somehow? Thermostat sitting flush in block? I haven't had this issue, just throwing out ideas..
 
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JMT said:
I’ve been there. Very frustrating. Make sure it’s not the water pump leaking. Get the surface prep perfect. I’ve had very little luck with the gaskets (fel-pro, off brand). I tried with and without permatex RTV. If the thermostat is an off brand it’s surface may not be flush. After 4 gaskets I gave up and bought some of The Right Stuff 1-Minute Gasket Maker (black). Go around each hole and along the mounting surface in a continuous bead (as best you can). Solved. NAPA stocks it.

Don’t forget the hole in the thermostat should be at the top.
Click to expand...

Did you use the Gasket Maker with a new gasket or no gasket at all?
 
oldjeepman said:
I would clean the engine side with a razor blade scraper really good. Maybe housing is warped somehow? Thermostat sitting flush in block? I haven't had this issue, just throwing out ideas..
Click to expand...

Thanks. I cleaned both surfaces thoroughly with a scraper, and wire-wheeled the housing mating surface. Didn't check for warpage but it wasn't leaking before.
 
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diggerwolf said:
Thanks. I cleaned both surfaces thoroughly with a scraper, and wire-wheeled the housing mating surface. Didn't check for warpage but it wasn't leaking before.
Click to expand...

Be careful wire wheeling the surface of the block. There are micro indentions in a pattern to aid in sealing the housing to the block. You’re probably fine. I did use a wire wheel too, just don’t want to go too far.
 
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freedom_in_4low said:
You're sure the thermostat isn't slipping out of its indention and getting between the housing and the head? I use some RTV to stick it in place while I mount the housing.
Click to expand...

X2 on this. Happened to me during the initial install of the thermostat. T-Stat kept slipping. I used a small dab of RTV to hold it in place as well. Solved the leak.
 
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Also, that slot on top of the grill. Dropped my ratchet in there and now it's stuck between the radiator and grill. Had to go buy a telescoping magnet to get it out. Dammit.
 
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Mike Z said:
X2 on this. Happened to me during the initial install of the thermostat. T-Stat kept slipping. I used a small dab of RTV to hold it in place as well. Solved the leak.
Click to expand...

My LJ was put together that way when I bought it. Had half a pound of RTV globbed on around the bottom bolt.
 
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diggerwolf said:
Also, that slot on top of the grill. Dropped my ratchet in there and now it's stuck between the radiator and grill. Had to go buy a telescoping magnet to get it out. Dammit.
Click to expand...

Hang in there. I dropped a ratchet down there when I was looking for the ambient air sensor for the compass/temperature mirror. Had to get me a good telescoping magnet. Learned not to keep my tools at the top of the grill anymore ;)
 
Been there.

Really clean out the housing surface..... especially around the ears where the bolts go thru.

I used rtv and a felpro gasket.
 
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This happened to me. Make sure the thermostat is sitting in the seat of the thermostat housing. I had mine slide down and unseat causing me not being able to properly tighten the housing due the the gap it left. I dabbed a couple spots of rtv on the thermostat housing seat and put the thermostat on there to act as an adhesive and have never had a problem. Good luck
 
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Since all the usual leak possibilities have been addressed in the previous responses, the thermostat housing was not leaking previously; you have already thoroughly cleaned both mating surfaces and there are no gouges or vertical lines on either the head or thermostat housing and IF the thermostat is staying seating in the recessed area of the head.
Where is the leak actually coming from ?
Is the leak coming from the heater core hose not seating properly due to corrosion on the hose nipple ?
Is the leak coming from the radiator hose not seating properly due to corrosion on the hose nipple ?
Have you checked the thermostat housing for cracks where the bolt holes pass thru ?
Have you checked the bolt holes in the head for hair line cracks that enlarge when a bolt is threaded and tightened ?

The use of a Felpro gasket with the impregnated sealant on one side and the adhesive on the other; you shouldn't need to use RTV if the surfaces are thoroughly cleaned and there are no deep scratches or cracks in the mating surfaces.
 
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Potomus Pete said:
Permatex makes an antifreeze ready gasket maker.
Click to expand...

42589626-6E4C-4CEB-A908-4F5A1459C1D7.jpeg

Is this what you are referring to?
 
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