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69 427 cooling system


New member
Jul 1, 2023
Nova Scotia
1969 coupe 427 4 speed blue
Hi , I’m new to this site . Hoping I can get some insight into an overheating issue with my car . 69 427/400 hp 4 speed no air . I have run into conflicting info on the proper configuration of the cooling system for my vehicle . At the moment I have a copper rad with an aluminum expansion tank but since I got the car on the road last year it has been running hot . My question is with a radiator with a 15 lb rad cap and a n expansion tank with a 15 lb cap as well , is this system going to work or where I don’t have an aluminum rad that wouldn’t have a cap on it should I forget the expansion tank and run the 3/4” heater hose direct from water pump to heater core and set up an overflow tank ? Sorry so long winded .
First of all you should make sure the copper radiator is not clogged in any way. Also when you added coolant did you add it slowly? You may have air in the system which would cause it to overheat. I have the same configuration as you do on my 68 big block and living in Southern California I do not have any overheating issues. If you wanna play it safe purchase a 3 or 4 core aluminum radiator.
Thanks for your response . The car has been completely restored ( new rad , heater core , water pump , thermostat etc . ) did the slow fill of system and there is flow through all hoses . My concern is this car was originally equipped with AC but I omitted with the rebuild but I kept the aluminum expansion tank configuration but some of my research suggests a copper rad in a big block doesn’t use the tank . Tank was there to pressurize the system as the aluminum rad ( original ) did not have a cap of its own . My question is will the cooling system work properly with the rad and expansion tank both having 15 lb pressure caps ?
You shouldn't have any problems using a 15 pound cap. How many core copper radiator do you have? With a big block you need a four core.
It’s a 4 core . Does your car have a copper rad with a filler cap ( 15 lb ) and if so , does your car have the aluminum Harris pressurized expansion tank ?
On my 68 NCRS I have a four core copper radiator and the aluminum expansion tank. If you have a four core radiator you should not be overheating unless you still have air in the system or something else like a bad clutch fan.

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