cooling issue....custom car

[dudemaaan]

I use a 16 psi cap. Coolant Pressure is related to the temperature of the coolant. As the coolant gets hotter it builds up more pressure. if your cap is old and weak or rated too low for your application the water will escape, this means it's not cooling the engine. Usually you have a water reservoir that catches the water, and when the coolant cools it sucks it back in. If you run a cap pressure too high, this puts extra pressure on the coolant hoses and seals under overheat conditions. I prefer to run a higher then stock pressure cap, this insures the coolant is still trying to cool the engine if temps ever do get high.

A system under normal operating temps will have the same pressure with a 16 psi cap as it will with a 13 psi cap. The only difference is when the temps go higher the 13 psi will boil over quicker.

hope this helps. And given your somewhat complicated system I wouldn't be surprised if you have air in your system. There is a special coolant burping funnel that is supposed to work well for this. I would try to burp your system over several days to insure no air is in there.