Looking for advice from the brain trust.
I have a 1979 300SD 102,000 miles, om617 engine.
Noticed a coolant leak from the top hose where it attaches to the radiator. The odd thing is the engine was cold. It had not been run in about 10 hours. I squeezed the hose and it was hard (under pressure). I took off the catch tank cap and a lot of pressure was released. I started thinking I had a bad head gasket.
I ran a combustion gas test on the tank and it came up positive. I did a pressure test on the coolant system while the engine was hot. The pressure leaked down from 10 PSI to 5 PSI over the course of a half hour. I am still thinking head gasket.
Now it starts to get odd. I ran a compression test (while the engine was cold with all injectors out) and came up with 302,305,300,301,303. All appear good. So I am thinking the gasket is fine,
The car does not overheat ( temp gauge stays a hair above 174). Changed the oil and did not see any sign of coolant. No signs of oil in the cooling system.
I recently replaced the thermostat. I found several intake/exhaust manifold nuts were loose, I recently tightened those. I rebuilt the turbo.
So what do you guys think. Could the compression test be invalid because the engine was cold? Could something else be pressurizing the coolant system? Maybe a crack in the head that opens when hot and closes when cold? Should I pull the head? The car is a keeper/daily driver, if I have a head issue I would like to solve it before I damage the engine any more.
As always I appreciate all thoughts.