I agree with Eric. I have found that I get the best coolant performance when using an original GM (made by Dole Valve Co.) thermostat with a 168 degree rating. Originals can be found in junk yards and checked with a pot of water on a heating source and a good thermometer to check its opening temperature.
what apain in the arse to replace….180* also found out where the puddling was coming from on the back of the intake manifold. The bypass hose was leaking and ran down towards the back. unfortunatly the water pump i replaced last year went t.u. have my orginal on its way to the flying dutchman 3 yr warranty..