I have a 69 Z28 with a 302. when i bought it it was overheating. i checked the thermostat, found it did not have one. I put one in, used a gasket, some silicon sealant and now it leaks out of the housing on the left side (if standing in front of the car). it is coming from the "post bolt". The housing is orange and i believe original, so is the manifold. It is tightened down evenly and I made sure not to overtighten. what am I doing wrong?

 

Its probably warped .You can use a file and or a sheet of sandpaper on a flat surface to level it out . I have a 1979 Z-28 with a supercharged small block and a 1981 El Camino SS 290 HP 350 And I use Fel pro "o" ring gaskets with lock washers with no leakage .

 

I've done the sand it flat method before, lasts until the flange warps again, which it will. Unless you're after originality, buy a performance neck that has a thicker flange. And yes, the o-ring seal type of flanges work well.

 

Thick flange as mentioned above is correct. However I took a piece of 80 grit and taped to a flat smooth surface (in my case a extra piece of counter top granite I had laying around, but you can also use a piece of glass)
then put the base of the neck on the sandpaper and sand back and forth. You will immediatly see low places on the neck that the sandpaper is not touching. Keep sanding until it hits all surfaces.
I made sure there was a good amount of sanding marks on the sanding area so to better help adhere to the intake with a gasket.

 

thanks. had it sanded then put the thicker plastic gasket and it worked.