JP --

After installing a new water oump (what I really mean is draining the cooling system), it's common to have no heat, and also to experience a giant "BURP" from the cooling system.

An air pocket can form in the block and also in the heater preventing complete refilling. Also, this air pocket can get into the pump, impeding circulation (pumping) and allowing the engine to overheat slightly at the initial start-up.

Open the heater valve fully (to permit flow), allow the engine to cool, refill, and retry.

After you get the car running and the engine temp stabilizes, recheck the coolant level.

Avoid scalding yourself.

"...now have a big coolant leak..."

This might be a real leak, or it might simply be the burp. Nonetheless, carefully examine the "mushroom" seal 'tween the pump 'n head, the O-ring where the heater pipe connects to the pump, and around the pump-to-block gasket.

Don Foster (near Cape Cod, MA)