[RayK]

I had the same problem. I used one of those reverse poppet units and it jammed up sideways in the housing!! It was brand new and I couldn't figure out why my 455 was running about 200 + degrees. I even checked it before i installed it to make sure it opened up at 160 degrees which it did. I put in one of the balanced units someone mentionmed and haven't had a problem since.

[RAIV55]

Good information, had the same problem but made a shim to hold the thermostat in place.

I was aware of the two designs of thermostats but didn't know the balanced sleeve syle was the prefered one for performance use.

Thanks

[GoatDr]

Pardon me if I'm wrong, but doesn't the gasket fit above the thermostat and hold it in. Put the thermostat in, next the gasket and then the thermo housing.

[RAIV55]

Originally Posted by GoatDr

Pardon me if I'm wrong, but doesn't the gasket fit above the thermostat and hold it in. Put the thermostat in, next the gasket and then the thermo housing.

The Fel-Pro thermostat gasket didn't hold mine in place. Guess I just figured the housing would retain it, which it didn't... well not in the right spot. My fault for not checking to begin with.