Leaking around the thermostat housing

Hello,

Are you sure that you got the correct neck for your make and model of vehicle? Also make sure that the gasket isn't pinched or binding in any way. The intake manifold or head, whatever the neck is bolted to might have a hairline crack where the bolt bolts into. Try this trick, smear some RTV, preferably the red high temperature, on the threads of the leaking bolt and then re-tighten. Wait for a couple of hours to make sure it's good and cured and then test to see if it sealed. Get back to us with what you find out.

Thanks,
Alex
2CarPros