ok, i just replaced a radiator in my 1988 dakota. Good truck, but the wear parts are 20 years old. the pressure cap was still good (relatively new). On this new radiator, when cold, I can squeeze the upper hose and fluid will flow into the overflow tank.

Am I correct that the outlet to that overflow tank should be sealed unless pressure is forcing coolant out, or a vacuum is pulling coolant in? other wise it should not open flow when I squeeze a hose.

Fyi: I tried this with about 5 different caps from dodges of the same era. they all did it, so did my 1986 Ram charger (slightly larger radiator but same size cap, with higher pressure)
Please let me know if i'm just paraniod or just crazy

 

My radiator is the same way. Its the radiator. Some how it needs a slightly longer body. I just got another rubber gasket from another cap and installed it and now it seals. There might be a spacific cap but I havnt found one. All I can find is the shorter one not the longer one.

 

what gets me the most is that my other truck does it also. it has an original radiator. I'm thinking, that the coolant is boiling but condenses back to water by the time it gets to the over flow tank. Then it gets sucked back into the system as a liquid like normal.

While this may work, the system is still not functioning properly. Still gotta get to work, I guess I'll carry an extra jug with me until I can fix it.