I have replaced the thermostat housing with the aluminum available now but I can’t get the hex head cap from leaking. I have installed the o-ring that came with it although it was ill fitting. This seems simple enough (famous last words) but I can’t seem to get a good seal. What has been done that worked?

 

Did you cross thread the cap? I have the aluminum unit and have had no issues. I also just looked at the old plastic cap. It has a gasket but not a traditional oring.

 

I do t think I cross-threaded the cap. The o-ring that came with the kit just doesn’t seem to seal. As for the thermostat I installed it the same as the one I removed. I tried the gasket from the old plastic one but that didn’t work either.

 

4.0 2002 v8 and I have been seeing the same cap leak also since the cold weather arrived. I’m guessing it’s because the metal shrinks when cold. Not sure it’s worth worrying about since it’s hardly sweating but definitely annoying. Should be able to replace cap gasket if your losing a lot of coolant maybe even a rubber seal from the hardware store could shore it up?

 

put the plastic cap on it

or even better, just put a plastic housing in it

 

It’s actually leaking more than than I can live especially after going through the trouble of replacing. I am planning on trying to fit a flat gasket on there.

 

Now wait Xalty,

Let's not get logical about this. Anyway, that aluminum housing or cap could have a crack that opens when hot. It could be the cap was tightened too much and the gasket is ruined. A cross threaded cap or housing that will never seal. The last thing I can think of is a metal burr that doesn't seem like a problem, but... There isn't much else to go wrong with this housing.

 

Well I gave up with the aluminum housing and bought a new plastic one, seems to be good. Now on to replace the front struts and on and on…..

Thanks everyone for the input.

 

Hey Rayz, for what it's worth, this happened to me as well -- bought the URO one through Moss. I ended up going up 1 size up on the o-ring versus what came in the kit and it sealed easily. Very strange quality issue, but I wasn't going to swap it out after I did the installation.

 

I struggled with that darn cap and just wanted to move on so I went back to the plastic one even though I felt the aluminum housing was the way to go. I have recently put everything back together and I’m happy to say no leaks. As I mentioned before I went ahead and replaced a bunch of parts while I was in there (fuel injectors, fuel injector pigtails, intake gaskets, spark plugs and coils. Now I’m back to finishing up the front suspension, struts, A arms, stability bar links and steering rack links.