08 chu613 with mp8 coolant system issue

[eric787]

I am new to working on macks so bare with me.. We have a 08 chu613 with the mp8 motor, intermittently over heating. Can run all day fine then over heat end of the day and also its winter right now in new england so keep that in mind that it is not running in hot temps. For starters, is it normal for this truck to be ran on a Saturday then come back on a Monday morning with a lot of pressure still built up in the expansion tank? If so then I can exclude that from diagnosis. Couldn't get the truck to over heat for me but it does for the driver randomly. Fan kicks on as it should with no codes. Only codes it had was for coolant temp after it got real hot he had to pull over and let it cool down. Did combustion gas test with napa tool came back negative... Dpf doesn't seem plugged. Popped off outlet side of egr cool just black soot no coolant crust that I could see. Should i consider takin off inlet side and looking? Also best way to test if it is the compressor that is building the pressure ( if the pressure build up is even abnormal ). Fan clutch is about a air old and kicks on as it should. new expansion tank cap. Not sure on my next move, any feedback would be greatly appreciated , thanks