eric787 Posted March 14, 2023 Share Posted March 14, 2023 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 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted March 14, 2023 Share Posted March 14, 2023 thermostat ?? Quote Link to comment Share on other sites More sharing options...
eric787 Posted March 14, 2023 Author Share Posted March 14, 2023 (edited) sorry forgot to mention that is new also. that was first thing i did after it over heather the first time Edited March 14, 2023 by eric787 1 Quote Link to comment Share on other sites More sharing options...
fjh Posted March 14, 2023 Share Posted March 14, 2023 55 minutes ago, eric787 said: sorry forgot to mention that is new also. that was first thing i did after it over heather the first time So I have a thought you can try! Drain the air tanks at the end of the day and see if you still have pressure in the morning! also these had issues either surge tanks cracking not sure if an over heat could be caused by this however it’s an honourable mention! It sounds like a combustion in coolant issue to me I’m not a fan of the combustion test cocktails they are hit and miss! Quote Link to comment Share on other sites More sharing options...
eric787 Posted March 14, 2023 Author Share Posted March 14, 2023 I will give that air tank tip a try in next day or 2. I am debating whether or not to pull egr cooler off and smoke test it. so I am assuming coolant system being pressurized for 24/48 hours after not being driven is not normal in these trucks correct? Quote Link to comment Share on other sites More sharing options...
fjh Posted March 14, 2023 Share Posted March 14, 2023 No 1 Quote Link to comment Share on other sites More sharing options...
eric787 Posted March 15, 2023 Author Share Posted March 15, 2023 UPDATE: Ran it for 5 min this morning with everything connected to see if cooling system built pressure and it did. took cap off expansion tank to release pressure then put it back on. disconnected coolant lines from the air compressor and clamped them closed. cut fingers off rubber gloves and zip tied them onto the coolant out let and inlet on the compressor. fired up the truck and the rubber fingers started to inflate and could see air and left over coolant sneaking past the zip tie also very very little pressure in coolant system after doing that. going to pull air compressor out now and take a look at it. 1 1 Quote Link to comment Share on other sites More sharing options...
Solution eric787 Posted March 31, 2023 Author Solution Share Posted March 31, 2023 air compressor fixed it 1 Quote Link to comment Share on other sites More sharing options...
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