feeling the pressure

[MESTWHT]

so my cooling system seems to be in serious trouble.
my car has been overheating the last couple of days and i'm having a hell of a time coming up with the problem. soon as the engine starts to crank it builds crazy back pressure through the rad.
problem seems to be at #2 cylinder, did a compression test earlier, got 125psi at 1,3,4. #2 was 105psi and caused the back pressuere in my rad with the compression tester hooked up.
i did a pressure test on the cooling system, held 16psi fine. ran the motor withe the pressure tester hooked up and it went up to about 10psi in the 2 min it was running. doesn't seem to be coolant getting into the oil... been dead on the full mark everytime i checked. if i let the car get ice cold, and top up the coolant, it seems fine. close the rad and run it for (honestly), 10seconds, it'll blow coolant everywhere if i open the cap.
can anyone give me any suggestions as to what may be up? i even pressurized each cylinder and none of them showed back through the rad, it only happens if the car is actually running.
thanks in advance, hope someone can help.

[NAJ]

The Cooling System is a Totally Sealed System.The only thing that can cause that kind of Pressure Increase that quickly is Compression entering the System which would be caused by a Head Gasket,Cylinder Head or Block Problem. You probably need to run a Cylinder Leak down Test.

[MESTWHT]

and how do i do that?

[NAJ]

"Google" automotive how to cylinder leak down test.There are numerous links.
You can also try installing your compression tester and then pressure test the cooling system to see if you get any pressure reading that will help narrow down which cylinder is at fault.
If you pressure test the cooling system with all of the plugs removed does the gauge hold pressure? do you hear any air leaking? Is there any signs of coolant in any cylinders?

[MESTWHT]

i did try pressure testing the motor with the plugs out... held fine.
turned it over a few times with the plugs out, no coolant showed.
i'm pretty sure #2 is the problem. like i said, during my compression test, that cylinder was low, and showed back through the rad when the compression tester was in the spark plug hole

[NAJ]

Unfortunately these are the only tests we have to diagnoise and locate a problem such as this. There is no way look in there and see what is actually happening.Maybe someone that has experianced this sort of problem will post and tell you what they found otherwise you will probably be removing the head.

[lennylebaron]

I had the same problem with my caravan. Mine was the more common head gasket failure on the back side of #1 cylinder. However my lebaron always had a miss that I couldnt track down and then one day it started drinking antifreeze, about a cup full a day. About a week later I had a full throtle battle with a 5.0 and it started smoke/ fog screening like somthing out of a frickin james bond flick. Pulled the head to find that it had some very large cracks in all of the bowls and some in between the valve seat areas. The one that finally let go was on #2 and must have been the culprit for the miss because the surfaces on face of the valves were green just like antifreeze. Moral of the story is you really cant tell till ya tear her apart.