Puking coolant

[Coco620]

Hello,
A friend of mine has a cm871 keeps puking coolant out the over flow if he loosens cap a enough to release pressure it sucks it suck the coolant back where it belongs, same if he starts truck back up;Any ideas? Thanks in advance.

[Waterloo]

Head gasket or bad head. How many miles on the truck, and does it still have the mandate? That is what mine did when the head went. At the end, it actually blew my radiator into pieces, it was building that much pressure in the system. Took her in and did a total in frame. If it is a bad head, do not reman it and do not put a Cummins reman head on either! Only NEW OEM, these heads are one time use only.

Tell your buddy to call the local auto parts store and ask for a block test kit. Napa stocks them. If you have exhaust gas in the system you will know in a matter of seconds.

Also, rare, but happens, the air compressor can cause the same symptoms. I forget how to test for this in regards to pulling the lines. What I did is drain the air tanks, left the tank valves open and fired up the truck. It was the head.

[Rawze]

The only time i have ever seen a bad head gasket on an ISX without it being a liner, the head had been under-torqued. I.E> --> if it is building pressure in the coolant system and it is from the head gasket,.. It will have fretted liner too, even if the heights check out good. If it is not corrected, it will simply do it again in short order.

[Coco620]

Thank you very much guys I will pass it along ,no mandate .