Radiator Overflow Tank

I'm running a 59AB flathead with Walker radiator and electric fan in my 33 Ford PU. The truck runs a 185-190 temp. However, coolant blows out my over-flow tank. What's the problem?

 

How good is your radiator cap and what pound is it?

 

PRESSURE TEST YOUR RADIATOR CAP FIRST. As engines heat up they develop temperature as well as pressure. Let's say you are making 10 p.s.i. and you only have a 7 p.s.i. cap, your cap will vent off 3 p.s.i. What was your system designed for? I don't know either. Pressure test your cooling system to see what pressure it will hold. Check the top of your radiator cap, it should be marked. Most systems will handle 15-16 p.s.i. Not sure how to do this, have a radiator shop test both of them for you.

 

You may be overfilling your overflow tank. When the coolant expands, it has nowhere to go but out.

 

Let it overflow until it stops then check the water level in the tank. That's how full it should be.

 

Fill the radiator until fluid just covers the inside fins....no higher. This will give you 2+ inches of expansion area. I also installed an overflow on my flathead, but don't get any fluid in it. Electric fan works fine. Use a 7# cap on the flathead.

 

running a catch can or over flow closed system are different. If just running a catch can
do like Ford Guy said. if running a closed system need to have radiator full, close to base of cap. so that as system cools it will draw coolant back into radiator. what mix of coolant are you running? tried any of the additives that help cool system? no signs of head gasket problem? fan have shroud? stock motor?