could I have good compression in all cylinders and still have a head gasket leak?

renix 1988 4.0l closed cooling system

Could I have good compression in all cylinders and still have a head gasket leak or cracked head?

cylinder psi readings
1 125psi
2 140psi
3 140psi
4 132psi
5 125psi
6 130psi

If i leave the pressure cap off the fill bottle, when the engine warms up, fluid will boil out. Should It do this? does this mean exhaust gas is getting into the radiator fluid. The fluid looks a little foamy. The jeep is new to my buddy and the people he got it from said it was over heating on them. Any suggestions would be great. John McHorney

I doubt that you have any problem with neither the head nor the head gasket so the answer to your first question is no, unless the leak is between the crankcase and the water jacket rather than between a combustion chamber/intake port/exhaust port and the water jacket.
If you leave the pressure cap off, the coolant will boil away because you need the pressure to raise the boiling point.
In all likelihood, I think the radiator core is most likely to be severely clogged and if the coolant hasn't been changed for a long time, it'll look rusty and foamy. If the radiator is still the original '88 unit, it's well past its "best before" date and it's time to replace it.

I will flush the system and change the radiator tonight and tomorrow. It idles so nice. I also need a new football, it starts to leak when temp gets to 190deg.
thanks John McHorney

I had the same problem with mine and it ended up being the radiator. I took it to my uncle and he said a little plastic piece broke at the bottom of the radiator and messed with the return line..... sounded crazy to me at the time but I have not had a problem since. I hope this helps

Remember too that if this is the original closed system with the separate pressure tank, you should "burp" it after filling, by running it with the cap off. As it heats up, it will take a few big gulps, and require more coolant. If you don't do this, it may appear to be filled, but it isn't, and it will overheat once you hit the road.

Although nothing is impossible, a bad head gasket is less likely than a bad radiator, and a problem bad enough to cause overheating would more likely show a bad cylinder or two adjacent ones with low readings. If you're really concerned, you can get the system pressure tested (if you can find a pressure test adapter for the coolant bottle) or "blow it down" using compressed air into the plug holes. A blowdown should show if there's any leakage into the cooling system.