Is the engine rpm steady? Does the pulsing stop if you rev it up a little bit? Maybe it's just the Chevy heartbeat?

 

only notice it at idle. It runs smooth and i wasnt able to get it to do it without a thermostat in it. I hope its normal but even being a mechanic for awhile ive never seen this happen

 

Can you account for all the pieces of the thermostat that fell apart?

You see where I'm going with this.

 

I seem to have everything, but yes I do see where your going and I was going to try flushing things out next to try and find anything

 

I wonder if the spring in the stat is weak or something and the surge from the water pump is enough to open it. Although if install right, copper down, the pump pressure should be trying to close it. I dunno really, I'm just thinking and its pretty early for all that.

 

You mentioned a bubble in the cooling system. Any more I drill two 1/16" holes on each side of the thermostat to prevent bubble formation when filling the radiator the first time.

 

The stat I have already had a bleeder hole in it. Maybe it needs more or something I'm not sure. I know my radiator won't have any restrictions cuz I put a new aluminum one in. I have good heat too so I wouldn't think the heater core is causing an issue either

 

Is it possible the coolant is boiling. Does the pulsating continue when you turn the engine off?

 

Yes it does. My temp gauge never goes over 180 though

 

Hmm... In that case, does the system build pressure when running? If not, you're likely getting hot spots that are boiling.

 

It does build some pressure. What could be causing the hot spots?

 

The engine has spots that are much hotter than the rest of the engine; they tend to be around the exhaust seats and guides especially the paired exhausts in the center of the head, and the spark plugs which have local boiling of the coolant long before the bulk coolant temp is anywhere close to boiling. Plus this is a 400 which has problems at the upper ends of the siamesed cylinders with steam pockets forming under the deck; these should pass into the head through the 3 pairs of center vent holes between the cylinders but the heads and head gasket need matching holes to complete this coolant circuit. This engine is also very sensitive to having a coolant by pass that keeps coolant moving through the block when the thermostat is closed.

Bogie

 

Were the proper steam holes drilled in the heads and the proper gaskets used. The 400's had some special considerations. One of the more experienced engine guys can probably shed some light on the 400 requirements..
Just because the temp at the sender is 180* it doesn't mean it is the same temp next to the cylinder walls.
What are you running for a coolant mix.
I have seen coolant hoses pulse many times and it always due to boiling coolant. You proved it is not mechanical as it does it with the engine off.

 

Were the proper steam holes drilled in the heads and the proper gaskets used.

. X 2... also, I didn't realize there were Banks heads for gas engines...

 

I thought that's what the machinist said they were but I'm probably wrong. I have 400 gaskets and he drill the steam holes in them too. I'm running my mixture about 60/40. 40 is water

 

Thanks for all the information guys. I'm going to try bleeding it again and putting 160 star in it so hopefully I get better flow. I'm also getting a heavier duty water pump