Sounds like you have air in the system, did you bleed the air out using the bleeder screw on the thermostat housing?

 

No. How do I do that does the car have to be running? I purged the system through the radiator cap, maybe I didn't do it right.

 

if you have an LT1 then yes engine running open bleeder screw but put rags under thermostat so you don't get the opti wet

 

The Impala only has one bleeder in the thermostat housing. Get the car up to temp then open the bleeder and allow the air to bleed out. It helps if you raise the front end, or just park facing uphill a little.

 

Raising the front end will cause air to get trapped in the radiator. I found that out the hard way.

It helps if you raise the front end, or just park facing uphill a little.

 

That's interesting. It's exactly the opposite of my experience and all the advice I've read over the years. I wonder what accounts for that.

 

The problem is if you raise the front end of the car, you put the radiator at the highest point (above the thermostat housing's vent screw). With the car flat, that screw is higher than the top of the radiator.

So, raising the radiator above the screw will trap air in the radiator.

At least, that's what I've been told on our cars and I've only had to purge the air once the way I describe, not many times like I've heard others have to when they raise the front end.

Maybe I just got lucky.

 

IIRC even opening the bleeder on a cold engine and blowing on the expansion tank with the cap off can help push air bubbles out pretty easily