The Stovebolt Site Forums The Shop Area Engine Shop I need a further cooling system diagnosis

My problem: coolant flowing out of the overflow tube.

I put in a new thermostat and new thermostat gasket. I filled the block with coolant first. I topped off the radiator, but not too full.
Here's what happens now. I started the engine from cold. I walked back and forth from the open radiator cap to the temp gauge. As soon as the temp gauge showed warm, I looked down the radiator and could see when the thermostat opened 'cause the coolant rose up within the radiator and into the overflow tube.
Does this indicate a blockage somewhere?

Tips and comments please?

Hy Jim Bow, it might indicate that there is air trapped in the system some where. I would put the cap on and let the system sort out its comfortable level, it should only burp coolant out once, not every warm up cycle. If it does burp every cycle I would say you're introducing air into the system, through a possible head gasket leak, hope that helps.

as 3B says, let it find it's own level, checking the fill level cold is likely your only problem, when up to circulating temp it should be at least 1-2" down, as long as it's above the fins it'll be fine

Bill

If it was a head gasket leak, wouldn't I see a lot of bubbling?

I'll let it run a while and see if it seeks it's level.

Take the heater outlet hose loose from the Therm outlet or intake manifold & vent it till coolant comes out. Did you mix a 50-50 solution of A-freeze & water? Too much a-freeze can give poor cooling & foam.

3B and Squeeze, I did what you said. It got up to running temp and I let it run for about 20 minutes. It leveled off just as you said. I also discovered a water pump leak!

I pick up a replacement on Thursday.

Thanks for the tips.
Wrenchbender, coolant is 50/50. I'll do your heater hose trick when I replace the pump and do a re-fill.

The quick way to check for a compression leak, either a head gasket or a cracked head, is to fill the engine with coolant up to the level of the thermostat housing with the thermostat out and the upper hose removed. Take the fan belt off to disable the water pump, fire up the engine, and goose the throttle a few times. The engine will run for at least 30 seconds without boiling the coolant near the cylinder walls. If you see bubbles, or get a gusher when you accelerate, there's a compression leak.
Jerry