Hello everyone, need help.
Just built a 351w for my 68 cougar.
Around 450hp
When I get on it, it blows out antifreeze out of the cap.
I’ve got a 16psi cap on it.
Oem is 13 to 16.
Why would it blow out antifreeze when I get on it. ?
¾ throttle to full throttle is when it does It.
Runs cool
Idle for an hour, stays at 170 or so.
351w non roller block
Afr 185 heads
.021 copper head gasket.
11:1 compression.
Not usually a fan of parts swapping, but I’d try a new cap first.
Are you completely filling the radiator and do you not have an overflow recovery system? Water expands when hot and has to go somewhere. If no overflow recovery, water level when cold should be just above the interior fins in the radiator.
How do you know it only happens when you get on it? Sounds like maybe you are test driving it without the hood?
Put an egg under the gas pedal.
Or, you can try to tee in a fuel pressure gauge to a heater hose to see what the pressure is really doing. I’m suspicious of how the cap fits to the radiator. If it over pressures, it should go into the overflow reservoir. If it is blowing out around the cap, then the outer seal is not sealing. Could be the wrong cap for the radiator. If the cap isn’t held that tight, then the cap isn’t sealed to the radiator and also the pressure to blow off the relief is less than the spec on the cap.
Another possibility is a blown head gasket, with the compression pressuring the cooling system.
But start with the radiator cap.
You can check for a combustion leak from the head gasket with a block tester from Napa etc
I suspect a bad headgasket. easy to check with a block tester like mentioned or a pressure tester on the radiator
One indicator for a bad head gasket with a coolant leak in the cylinder is one spark plug might be cleaner than the others.
Wrong head gaskets.
Put on the 3 layer.
No more problem.
Ty everyone .