Pressure at rad cap?

[Ryan Colley]

I've recently had some issues with high coolant pressure at the rad cap (1988 6.2L). I was running with a 13 psi cap and noticed I was losing coolant at the cap (spraying out all over the battery etc.). I am now experimenting with a 16 psi cap - this morning I removed the cap (engine cold from sitting overnight) and a large amount of coolant burst out of the rad. What would cause so much pressure in the rad? I doubt I have a restriction in the overflow tank hose, but have yet to check. Is it possible its being caused by combustion pressure - head gasket blown???

[TimK]

Yes, it does sound like a head gasket leak.

TimK

[Ryan Colley]

No restriction in overflow tank hose...Still not seeing any bubbles in the overflow tank. Why would the pressure build up in the rad and not escape to the overflow tank???

Does anyone know anything about testing for combustion gas in the cooling system? Thanks!

[TimK]

Pressure will only get vented to the overflow tank if it exceeds the pressure rating of the cap.

For a normal working system that starts at zero psi when cold, it will return to zero psi when the engine cools back down again. If some of the water was forced out due to excesscive pressure, then when the engine cools it may actually be less then zero pressure and therefore draw coolant from the overflow tank back into the radiator.

TimK