I got a faulty Thermostat Housing from British Parts UK last year that had to go back. (full refund of my additional postage + 10% additional discount as recompense so no complaints about British Parts UK)

Threads on both the Housing and the Cap were badly machined and the Cap wouldn't screw on properly.

Without the O Ring fitted, the Cap should screw on with no force needed until the inside top of the Cap contacts the top of the Housing. If it doesn't, you won't be able to torque it properly or get a watertight seal with the O Ring in place.

If in doubt, post a pic of the Housing threads and the inside of the Cap.

Graham

 

When you get the new cap (should hopefully come with the correct O-Ring) - be sure to torque it down to 9Nm and you should be good....

 

I really hope its not a poorly machined thread on the housing because that would be a bitch and a half to do over again.
I called the local import parts place to order a new cap and they can only get a plastic one! what do you think about that? I had them order it anyway since it was $6 but I may have to go online to get another aluminum cap if the plastic doesnt work.
The threads on the cap did not seem to be machined very good so that could have been the issue and keeping my fingers crossed on the housing threads to be in good shape.
really really really dont want to take apart the housing again.
I have other issues to address on this untamed cat

 

Here's as a good a pic as I have of the housing without the Cap.



The threads are cleanly cut and also note the smooth finish on the Thermostat Housing body. The one I sent back was a very rough casting and, as well as the threads not being properly machined, was of poorer quality. I understand that there's a lot of these sub standard Housings around on the aftermarket.

As you are having problems getting a good seal on the Cap, a plastic one will be better as it is slightly more flexible that the aluminium one.

Graham

 

Thanks Graham. My housing seemed to be cast pretty good like the one you have there but the cap threads looked rough and when I screwed it on I could hear the metal grinding a little. Hoping the plastic cap seals her up nicely so I can stomp on the gas again without worrying about coolant shooting through the cap as I pass the many slow driving tourists in Hawaii.
Really appreciate the help and I nominate you for most helpful member of the month! haha cheers

 

Metal grinding is exactly how I'd describe the one I returned.

I know it's a pain to change the Housing but cooling is so critical on these V8's that if there's still a leak after fitting the plastic cap, it's the best way to go.

For your next job, remember the cam covers are also plastic! Good news is they are a lot more robust.

Graham

 

oh I definitely agree. If that plastic cap doesn't stop leak completely I will be returning the housing. keeping my fingers crossed that it was just a bad cap.
Thanks Graham

 

I would strongly consider returning the housing and getting a replacement - I would feel kind of skiddish putting a plastic cap on an aluminum housing - those plastic caps wear out over time. (Don't get me wrong - it should be OK for the short term though)

 

Thanks for the advice abonano. There has got to be some way to get an aluminum cap by itself right? Anyone know of a website that sells just the cap?
I would hate to rip out the housing just because of a bad cap thread and no one that will sell just the aluminum cap. The housing threads did not look bad but the cap threads are not good.
aloha

 

I have allso experienced a small leak from the rear of the thermostate housing. And at the same time I had bad performance form the cabbin heat system after the thermostate got fully open.
I therefore changed the thermostate housing with an aftermarket aluminium piece that probably won't break. The two rear 6mm screws was customized with a groove for a flat screwdriver at the top. That lead to a faster assembly.
Then there was this bleeding issue. My car is a MY96 where the engine has been replaced with a 98 engine. According to the Tech. Bulletin 303-15 the bleeder from the radiator has been omitted in the 98 models. In my car the radiator is 96, the expansion tank is 98, but both the bleeding lines was originally attached. After closer examination of the tank, the rear inlet pipe was plugged in the casting process. This rear inlet is the most important bleeding line on the 96and 97 models. So when this bleeding line was blocked it had to be some air trapped in the system, leading to the bad performance.
In this case I fixed the problem by drilling a proper sized hole in the rear inlet, because I wanted to keep the bleeding line from the radiator to avoid any uncerainity.
Pictures of the bleeding lines are covered by the thec. Note 303-15