Coolant leaking from radiator cap

[Waterloo]

Like Rawze says pressure test it... Been down that road, it was the head. BUT, mine would hold pressure right up to the end. I milked my CM-871 for roughly two years with that bad head. Then the fun began, the pressure was so great it blew my radiator apart and the coolant lines inside of the APU cases. Any coolant line that had the slightest bit of age blew apart. Then it was time, new head and in frame. You would open the coolant bottle and it was like a volcano!

One other thing that you can check is the air compressor. I don't know how yours is plumbed, but on the 871 it could cause issues like this, air/pressure in the coolant system. One of the guys can chime in if that could be a possibility on you particular motor. Hopefully it is something simple like this. If it is the head, don't reuse it, you will need a new one, not a reman. These are considered disposable items on the Cummins and should be replaced with NEW OEM. Good luck!