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88MJ Overheating

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'88MJ, 4.0, auto, kept overheating and losing coolant. Traced the overheating to a clogged radiator. No clue as to where the coolant was going, no leaks, no puddles on the ground, no water in oil pan. Compression check was 100-110 PSI on all cylinders. Filled the pressure tank and came back an hour later and it was empty. Refilled it, started engine. Went around in back and held hand in exhaust output. 30 seconds hand was wet. Cracked block or cracked head, or leaking head gasket. Going to pull head tomorrow. We'll see.

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FYI - 100-110 PSI compression is LOW.

You are correct. However I have always felt uniformity between cylinders to be more important than highest readings. It does 85 , and a little more, on the highway and gets 19-21 mpg so I'm not really worried about actual compression. Just where's the coolant going. Also the gauge has never been calibrated so who knows what the accuracy is?

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try pressure tester on coolant system and check the leaking again? maybe leak from heater core?


do you see any abnormal smokes come out from exhuast while engine running?


I have a great habit of not being able to find a tool so I go buy a new one. Immediately after getting home with the shiny new tool I find the old one. I have 3 pressure testers. I can't find any of them. I refuse to buy a fourth. Pulled the mats and floor boards are dry. Been busy so haven't pulled the head yet. The exhaust is clear, except for getting anything held in it 'sweaty'. Got an idea, going to pull all plugs, spark, and keep filling pressure bottle. Cylinder has got to fill up sooner or later and water come out plug hole. Maybe. We'll see.

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