2004 FL M2, 3126 Cat, blowing coolant

2004 Freightliner M2, Vin - M41405, 252k miles
3126 Cat, 250HP, s/n - HEP36720
Allison MD-3060-P, s/n - 1S6510436054

We are having an on-going issue with blowing coolant from the overflow tank.

All work has been done by a Freightliner mechanic duo with over 50 years combined experience. They are coming to the end of their suggestions before we do an in-frame.

Issue started 1.5 months ago: diesel in coolant. Determined a cup was leaking on the head. When they pulled the cup, noticed some pinholes, so they replaced the head with a brand new CAT head (from CAT). Liners were inspected from the top with no issues detected. Block was inspected with no issues. Replaced heater core as it has a small leak. No coolant was discovered in fuel side.

Truck back in service two weeks, overheated on a hill pull, and blew some coolant. Found water pump was weeping. New water pump, both thermostats and upper radiator hose replaced.

Truck back in service three weeks and overheated on the same hill. Radiator pulled, cleaned and flow checked with no issues discovered. Found two cracks in CAC - replaced; nearly clogged pre-EPA muffler - replaced with standard muffler; replaced radiator cap.

Truck picked up from mechanic and blew two gallons of anti-freeze in 30 miles (drive back to office). Put on second new radiator cap, blew again. Determined head on air compressor was charging coolant system. Replaced air compressor (new), new coolant and oil lines to/from air compressor.

Truck picked up from mechanic and ran correctly. First day with load it made approximately 6 miles to fuel station. When the driver pulled in, he noticed coolant blowing out. Only two small pulls and temp made it to approximately 200 on second hill.

Mechanic suggestion this time is to pull oil pan and inspect the bottom of all cylinder liners. Any other suggestions to cover are greatly appreciate.

 

Unless the air lines tie under the dash, it does not appear that anything is air controlled.

A combustion gas test is something I had planned to ask them to run before they pull the oil pan, but I'm not aware of it having been run already.

 

I will ask them specifically about this, but they indicated they had inspected the liners and block for wear when the head was replaced. I'm not saying they couldn't miss something, and I'm hoping the combustion gas test will help us narrow it down.