Hey, I've been reading forever, but now Have a problem with my SBC

Ok, here's the deal. My 38 Chevy (driving since 87) did a "freshen up" over the winter. Pulled heads, new guides, new Walker rad and cool mate fan. New thermostat.New water pump (hi volume) Got running, heats up what I see as normally, the fan cycles on at 200 and will bring the temp down to 180. Coolant Sensor in head.The engine "pounds" like a bad t stat. I changeed to a 160 degree. same thing. The upper hose collapses when I rev the motor(only sometimes) Changed the 12 lb cap for a 7 lb cap, even left it loose.Coolant still purges up and out of the cap when loose, and it still pounds. I can see the coolant circulating in the radiator , and it still feels like the T stat is closed. Drained it down a bit, pulled the upper hose, t stat wide open. It almost se4ems like an air pocket in the block. I did drain both block drains when i pulled the heads. Suggestions?

 

Welcome to the H.A.M.B.

I doubt it's related to the thermostat since if I'm reading correctly, it's happened with the first thermostat, and then with a 160 deg. I am curious as to why your top hose would collapse...this should never happen as with a conventional SBC, with std. cooling, the top hose is the return. It's not altogether surprising that the coolant purges when the cap is loose.

You say that you can see the coolant circulating in the radiator...do you mean that you can see motion...or that you can see coolant returning from the top hose? Given that you say the head temp sensor is showing a reduction from 200 to 180 (again if I am reading right), it sounds as if something's circulating to an extent.

Why exactly did you replace the water pump and radiator, along with adding the fan? (Not that you shouldn't have...but was there an overheating problem? Adding insurance?)

Can you give us the exact thermostat you used, and do you know the head gasket part number & brand? What are the details of the water pump, and is it a long or short style? Did you make any other engine changes besides the new valve guides? What are the head casting numbers? Did you have the heads milled at all as part of the work?

I'm inclined towards a couple of possibilities at first glance, but I'd like to know a bit more. One thing you might consider trying is to drill a 1/8" bypass hole in the thermostat...this can help to get rid of air pockets.

 

And get many more suggestions if this were on the main board instead if the introduction forum..Introduce your self and post there...Welcome by the way

 

wbrw32 is right - put your question out on the main board. Lots of Chevy guys out there that can help you out.
Welcome from O-HI-O
The Rock