2001 Chevy Impala

When you replaced the thermostat, did you also replace the gasket? If so, did you remove the old gasket material first? Sometimes the old gasket will stick to the mating surfaces, and prevent the new one from sealing correctly.

Remove the thermostat housing and make sure the two surfaces are completely clean of old material. (Don't put any scratches in the aluminum!) Then install a new gasket and make sure to tighten the housing down correctly, without over tightening it.

You can also place a thin bead of "High-Temp" silicon adhesive around the gasket to make sure. Don't use too much, and follow the instructions on the tube.

With the engine off and completely cold, wipe the area around the thermostat housing clean, including the hose and hose clamp.

Then start the engine and let it idle until the thermostat opens. The pressure should cause the leak to begin again, and since you have the area clean, it should be relatively easy to determine exactly where it's leaking from.

I suspect that the leak is originating from the hose or hose clamp. If so, you may have not tightened the hose clamp down enough, or you many have placed the clamp directly ontop of the nipple instead of behind it. This will cause a leak.

Also, you may have a small hole of crack in the hose. If you're sure you removed all old gasket material from the housing and used RTV with a new gasket, then it can't be anything other than the hose clamp or hose. Clean the area and follow my directions. Get back with me when you're done. We'll take it from there.