C-15 blowing coolant out

Most likely injector cups. When the O-rings fail on the injector cups it pushes fuel into the coolant. Check for fuel smell in the coolant, the diesel should float to the top in the expansion tank after the truck has sat for awhile.

 

Is this maybe one of those older Freightliners with a leaking air controlled heater valve that will put compressed air into the coolant?

 

Thanks to Caterpillar's fine engineering and good old big brother, more than likely it's a head gasket, low liners and high compression, but I'm a glass half empty kinda guy these days when it comes to Caterpillar, do the bottle test with air compressor unloaded and discharge line off, and watch for the bubbles, best of luck.

 

building mine due to it blowing coolant out....I got a head gasket then scored the liners!!

 

All your replies seem to have it covered. If there is no diesel smell in the tank, it rules out injector cups. As you know those compressors on the sdp prefix are junk, so don't overlook that.
Could possibly be cgi cooler but you should have that line capped somewhere. If you know what I mean.
I have seen a few low liner protrusion problems in that prefix just like the older ones.
I have a dummy injector made up that has A fitting in the top, also a good regulator and bleed off tap, I then supply up to 2000 psi of nitrogen to the cylinder. That soon finds which hole is open to the cooling system !

 

The truck gods may indeed be smiling on you, I would have sure bet on a head gasket, low liners, but for your sake I'm glad it's just the compressor, I hate to be all gloom and doom,It's just what we see here most of the time, no fun trying to explain to customers, who don't understand why low liners are such a problem, and so costly to repair correctly, that is if the block is true, and don't need to be decked, then that's another whole story in itself.