Hi new here , 

1966 Pontiac Grand Prix 

389 4 BB Automatic 

Just had engine redone soup to nuts . Had original Carter Carb refurbished i dropped it in new water pump , new 4 core Aluminum Radiator .

Engine starts up fine , runs good , sounds good but its overheating , thougt maybe water pump was defective got another one , took thermostat out still overheating , when looking into Radiator dont see any circulation .

My next step I'm going to by pass heater coil and run water into block .

I'm really hoping they didnt forget to take plug out of water jacket after painting motor or worse put head gasket on wrong .

Anyone have any suggestions because if my wife comes into the garage one more time her picture may end up on a milk container .

Edited May 25, 20251 yr by 66GP

Hmm...are you sure it's actually overheating? Factory gauge may not be correct if that's what you're monitoring. No air pockets in coolant? Have you tested thermostat by dropping into hot water in a pot on the stove and watching it open? Got coolant actually flowing through radiator - no factory packing or plugs not removed? Ignition timing correct? No collapsed radiator hoses? When water pump was replaced, was backing plate also replaced and clearance checked - gotta be minimal in order for pump to pump efficiently. Did engine take appropriate amount of coolant required to fill it as per factory spec? I've seen horror pics of rags left in engines and then engine runs - for a bit. Got plenty of fresh oil doing it's thing? If engine is freshly rebuilt it's gonna be tight for a thousand miles or so. They need to have done their machining correctly otherwise it might be too tight. Is it relatively easy to turn crank by hand, ie. socket on crankshaft pulley?

I really appreciate all your questions and the answers are all yes , everything is new .

At this point I'm leaning heavily towards clogged / bad heater core .

Tomorrow I will bypass it and see if that works .

66 GP has no temp gauge just a light .

The coolant is not circulating in Radiator ( Aluminum 4 core ) FLOW KOOLER Water pump  all new even bought a regular water pump thinking maybe Flow Kooler was defective. 

Everything is new and no issue hand cranking motor as I had to when bolting converter to flex plate .

I'm hoping and praying its the heater core and not that A ) when shop painted block they didn't block a water jacket and forget to remove or worse the head gasket is isn't set right but that I find really hard to believe because theres guide pins ( can't imagine someone f**king that up ) 

Sorry but I do not see how a blocked heater will cause the coolant to not flow to the radiator? Is the lower radiator hose collapsing when the engine is running? They used to put a spring in the lower hose to keep it from collapsing.

Other than that do you have the pumps rear backing plate installed? And is there a transfer tube installed with a good seal?

What type of impeller is installed on the new water pump? Is it cast or a generic stamped impeller? Those are about the only things I can think of that would cause a no coolant flow condition, other than a clogged hose or radiator.

 

Pictures of the pumps impeller and backing plate would help us T/S the issue, along with a picture of the timing chain cover with the pump removed.

 

Good luck

I like to thank everyone for their suggestion and help  Fitzy & Cammer Jeff you were both correct there are 2 divider plates that sit in the timing cover on was missing ! 

So basically the coolant was jusr sitting in the belly of the timing cover and the water pump was spinning but not moving the water .

Ordered 2 new stainless steel from Ames , yes I know I may have to modify a bit to have a close fit to impeller plate Flow Kooler pump .

And a big thank you to Larry at Hansen Racing in New Jersey the guy bleeds Pontiac knowledge .

Good to hear. I have a Flowkooler pump in my 389 and installed a nice new backing plate from Ames and the fit was perfect - I hope you are as lucky. I am very happy with the Flowkooler - car sits on 180° no matter what I'm doing with it.