Thermostat still leaks after replacement

[Agolding85]

After reading a few threads, this was my approach to stop this gasket from leaking:
1. Cleaned the block mating surface until it shined! No residue from previous gasket.
2. Used permatex high tack gasket sealer on the housing surface (used a new thermostat housing), placed the gasket on the housing, then painted a coat of gasket sealer on the opposite side of the gasket and mounted it to the vehicle
3. Painted a coat of the gasket seal on the threads of the bolts, let it sit for a minute before installing them
4. Torqued the bolts to 20ft/lbs and let it sit for 24 hrs before starting the vehicle or adding more fluid.
All surface were completely dry and clean before installing.
What else could be the problem. The leak is a lot smaller now, only a drop a minute, but it still leaks. Is there a specific way to seal the bolts? Would new bolts help? The old bolts looked pretty run down. And the latest leaking gasket appeared most worn down at the area of the bottom bolt hole

 

[The Real Lxxtsy]

Just use the thermostat gasket without any gasket sealer

 

[pagrey]

Some bolts go through to the inside of the block. You have to seal them or they will leak. I use plain black RTV on the whole thing. Put RTV, a thin coating on both sides of the gasket and make sure you have plenty of it on the bolts. Do not wait for the RTV to set, coat and install immediately. People are going to chime in and say you don't need RTV or the factory doesn't use it, after a few more attempts you'll ignore those people.

 

[Agolding85]

Just use the thermostat gasket without any gasket sealer

I tried that the first two times. The first was with the same thermostat housing it was already equipped with, the second time trying without a gasket sealer was with a new housing and it still leaked

 

[Agolding85]

Some bolts go through to the inside of the block. You have to seal them or they will leak. I use plain black RTV on the whole thing. Put RTV, a thin coating on both sides of the gasket and make sure you have plenty of it on the bolts. Do not wait for the RTV to set, coat and install immediately. People are going to chime in and say you don't need RTV or the factory doesn't use it, after a few more attempts you'll ignore those people.

How think of a coating on the threads? Should I coat both sides of the washer too? I’m desperate at this point, but don’t want to overkill the repair too much

 

[Agolding85]

How think of a coating on the threads? Should I coat both sides of the washer too? I’m desperate at this point, but don’t want to overkill the repair too much

*thick* of a coating...

 

[pagrey]

I'd fill the low points on the threads on the entire length of the bolt if that makes sense. You don't want a huge mess of it squeezing out but you do want to fill all the voids, especially where the bolts pass through the housing. Some RTV around the perimeter of the thermostat wont hurt but if you have a huge mess on the outside after you tighten it down you might try again. Ideally you want a little to squeeze out everywhere, just a bit.

 

[Agolding85]

I'd fill the low points on the threads on the entire length of the bolt if that makes sense. You don't want a huge mess of it squeezing out but you do want to fill all the voids, especially where the bolts pass through the housing. Some RTV around the perimeter of the thermostat wont hurt but if you have a huge mess on the outside after you tighten it down you might try again. Ideally you want a little to squeeze out everywhere, just a bit.

I’ll try that. I bought new bolts too. Not an expensive investment and it can’t hurt

 

[The Real Lxxtsy]

Just throwing some ideas out, are the hoses old or new that fit on the housing? hose clamps are tight?

 

[pagrey]

If you are using a torque wrench at 20ft/lbs they can be pretty far off at low settings. I'd consider tight with one hand and a 3/8 ratchet good but not really tight. Long way of saying make sure they are tight and don't just blindly trust a torque wrench. And like @lxxtsy says make sure it's the housing. I've had hose clamp problems on an aftermarket 4.0 housing because of interference with my valve cover.

 

[Agolding85]

Just throwing some ideas out, are the hoses old or new that fit on the housing? hose clamps are tight?

The hoses were all corroded when I bought it, so when I replaced the the thermostat, I replaced the hoses as well. Used the original hose clamps for the upper, and replaced the hose clamps on the lower for easier access. No leaks from the hose though. The drips are coming right at the base of the washer on the bottom bolt. At least that is how it appears. It does not appear to drip from the gasket. The drops land right on the anterior portion of the water pump beneath the bolt

 

[pagrey]

The drips are coming right at the base of the washer on the bottom bolt.

That's a good sign, just coat those bolts and you should be fine.

 

[Jerry Bransford]

I would avoid using RTV in addition to the gasket for the thermostat housing. Just clean the surfaces thoroughly using a fine wire brush and you should be fine where that seal is concerned.

For an emergency trail repair I once cut a thermostat housing gasket out of a piece of thin cardboard and it was leak free for several months before I replaced it with a gasket. It doesn't normally take a lot to get a leak free seal in the cooling system.

 

[qslim]

For an emergency trail repair I once cut a thermostat housing gasket out of a piece of thin cardboard and it was leak free for several months before I replaced it with a gasket

 

[CharlesHS]

Generally it doesn't take much more than a very thin coat of RTV to seal the gasket; I have even installed the housing without any sealant and it was leak free.
IF you are applying that much sealant even with new bolts then there is more to this leak than just a gasket that wont seal.
We had a Jeep owner with a 4.7L stroker that couldn't get the housing to seal no matter what he did....
During the process of thoroughly cleaning the gasket surface we found a hair line crack in water jacket bolt hole. To fix the leak we gently filed a notch in the crack, thoroughly cleaned the surface again and applied a coating of metal JB weld to the crack and inside the bolt hole. That was 10 years ago and the leak has not returned.

 

[pagrey]

Generally it doesn't take much more than a very thin coat of RTV to seal the gasket; I have even installed the housing without any sealant and it was leak free.
IF you are applying that much sealant even with new bolts then there is more to this leak than than just a gasket that

On some 4.0s like mine the lower bolt hole goes through to the cooling passage. For example if I remove my lower bolt and the gasket is perfect and still sealed coolant would pour out the hole. With the bolt in place the coolant spirals up the threads and leaks out where the washer is. Does that make sense? The gasket isn't really involved at all in this leak.

 

[CharlesHS]

I understand thoroughly what you are saying..., but he has replaced the bolts, applied an abnormal amount of sealant and it still is leaking... That is why I posted what we had experienced in the past.

 

[The Real Lxxtsy]

The only thing I can think of that can be the culprit is the area where the housing bolts on the block. Check the area on the block for cracks? Just an idea

 

[The Real Lxxtsy]

Also, was it leaking before you changed the thermostat?

 

[dbbd1]

My $32 mopar thermostat (brand new) housing had a crack in the casting. I just put on an $8 dorman. I'll check on it in the morning.