Cm2250 Air compressor or head gasket ?

[Waterloo]

I would go to NAPA and get one of their block test kits, they run around $50. Make sure the truck is warmed up, everything up to temp and then test. It may take a few minutes, but this test kit has worked 100% of the time I have suspected a head issue. It is the same test Cummins will run, it is in Quickserve if you want to look it up. Just make sure the fluid in the kit is fresh.

If that test shows nothing, and you still suspect the head or gasket, drop the oil pan and pressurize the coolant system. You will need to bar the motor, you are looking for coolant on the liner walls. On mine, you could actually hear the coolant gurgling when Rawze barred the motor. It was the #5 liner that broke loose.