Trouble sealing the thermostat housing.

[Milford Mustang]

I have tried twice to install the water neck and new thermostat and got a leak each time. I used the following procedure:
- put sealant on the water neck
- put gasket on the water neck
- put a little sealant on the water neck where the thermostat fits to hold it in place during assembly
- put sealant on the intake mounting surface
- gently take the water neck with gasket and thermostat and place it against the mounting surface
- tighten the bolts.

I must be doing something out of order or have method wrong. Looking for advice. Thanks.

 

[cobrajeff96]

Are you waiting for the sealant to fully cure before running the engine? When it comes to sealants my general rule for myself is to wait at least half a day, ideally a whole day.

 

[Milford Mustang]

Are you waiting for the sealant to fully cure before running the engine? When it comes to sealants my general rule for myself is to wait at least half a day, ideally a whole day.

Yes, I waited a whole day before I tested it.

 

[cobrajeff96]

Maybe there's too much setup gap that the sealant can't do its job?

 

[whiplash473]

I had this problem last year and it turned out to be (or what I assume to be) the gasket. I did the job three times with the same gasket and it leaked each time. Then I bought a different gasket the fourth time and it hasn't leaked since.

Three Fel-Pro gaskets failed. The cheap-o parts store one ended up being the one to not leak. I also didn't use any sealant.

So perhaps try a different gasket. Before my experience I would have never considered it.

 

[ttocs]

just to start stupid so we don't end up feeling stupid, I know it is hard to do but if ya try I thought you could put the thermostat in backwards but that it doesn't seal correctly when you do this?

 

[Milford Mustang]

I had this problem last year and it turned out to be (or what I assume to be) the gasket. I did the job three times with the same gasket and it leaked each time. Then I bought a different gasket the fourth time and it hasn't leaked since.

Three Fel-Pro gaskets failed. The cheap-o parts store one ended up being the one to not leak. I also didn't use any sealant.

So perhaps try a different gasket. Before my experience I would have never considered it.

I was wondering about the gasket as a culprit. I used Fel-pro both times. I will get another brand for the third try.

 

[Milford Mustang]

just to start stupid so we don't end up feeling stupid, I know it is hard to do but if ya try I thought you could put the thermostat in backwards but that it doesn't seal correctly when you do this?

I do not think installing the thermostat backwards is a good idea even if it fixed the leak.

 

[Milford Mustang]

Maybe there's too much setup gap that the sealant can't do its job?

Could be, I am using an aftermarket water neck. It seems flat enough but could be off.

 

[Mr horsepower]

Put a straight edge (known straight) on the water neck, you may find it is not flat. There are a number of the aftermarket housing that are KNOWN to not be flat. Also as said above, use a better gasket than the FelPro which are paper thin.

 

[ttocs]

I do not think installing the thermostat backwards is a good idea even if it fixed the leak.

well, yea it isn't a good idea and it can be really simple to have it flipped accidentally. As I said it is designed to only really fit in the one direction but if you try hard enough you can almost kind of get it back into place. Almost being enough to put it back on the block but not enough to seal/work correctly.

Another possibility is that if this is a 94/95 the coolant cross over tubes have some o-rings inside of them to allow for installation that are known to go bad/leak. If this is a 5.0 and you are noticing pooling behind the housing check the black pipe that comes up from the lower intake and see if it is leaking from there.