thermostat housing leak

I know that this is an old thread but here's an update. I used the aftermarket one pictured below and it leaked badly. The first thing that I did was take it to work and true up the gasket surface on the lathe. WOW this thing was way out!
I reinstalled it and it leaked again but just a trickle. So I took it off again and re-machined it. This time I did what we've been doing on Harley Davidson cylinders for years. I turned a small step (.005" high) onto the gasket surface. You can see the red line in the photo. That's the step. I reassembled it with Permatex and let it sit overnight. It is now perfect.
I hope this helps.


Ted