Intermittant over heating, Blown HG?

[kendem]

My engine overheats on the strangest occasions, and spills into the recovery tank. I was told I might have a blown head gasket.

Although there is no indication of any coolant mixed in the oil or vice versa.

So I tested the CO2 in the radiator using that chemical combustion tester and it stayed blue, detected no CO2. Tested several times with the engine running and looked ok. I made sure the chemical did work by testing it with the exhaust from the muffler and actually breathing on it and sure enough it turned yellow.

So then did a compression test and all 4 cylinders each registered in between 150 - 165 psi. According to the FSM they should be at 179 psi and not below 151 psi. Each adjacent cylinder was no more than 5-10 psi difference.

I tested each cylinder 3 times and got a slight variation each test of about 1-5 psi. By adding a little oil in the cylinder the psi came up slightly.

So it looks as if my compression on all 4 cylinders is on the low side, but that could be from worn rings? The engine has over 300K on it. Also all 4 spark plugs looked grayish. Probably from running lean.

In conclusion,
I think my head gasket might be ok. Maybe it is just the thermostat or radiator. My wife's Honda civic also has a similar issue where the coolant was spilling into the recovery tank and I changed the radiator and that solved the problem.


I welcome any comments.

[PapaSmurf2k3]

Yeah, take a look at your water pump. Have you ever replaced it? Is there any coolant coming out of the weep hole? Have you done any work recently to the cooling system that could get air bubbles in there? If so, have you bled the system?