12.7 Detroit burning coolant on startup sometimes???

I bet it burns it all the time. I'm thinking its pooling on top of the piston(s) when its shut off and you're seeing that excess burn off when you first start it. Probably once its running its such a small leak that its barely noticeable in the exhaust.

 

Bingo! Thats my guess. Maybe the reason it’s worse sometimes on a cold start is because there’s more coolant on top of the affected piston, depends where the piston is at in the stroke. Even with a very slight leak, if it sits long enough and gets enough coolant sitting on top of piston, then it will vapor lock when cranked. Coolant won’t compress. If the engine fires right off, might bend a rod as it gets to TDC. Drain a bit of oil, after sitting a while. Might find coolant settled in the bottom of pan. If so you’ll know for sure. Might be at risk for a catastrophe. I had that problem. Luckily, I was also losing prime. It didn’t fire right up. It did vapor lock, though. Starter isn’t powerful enough to bend a rod. I was able to bar it over by hand, squeezing the coolant past the rings into the pan, pull the fuse crank it and then popped the fuse in and got it started. Another Truck, another time, gasket was leaking and eventually blew completely while idling, it was too late. Had to be towed to the shop. I’d check the oil for coolant right away by draining a bit. Even if the oil looks fine on the stick, you can’t tell. If you find coolant in the pan, you might want to pull the ecm fuse, crank it over to make sure it doesn’t vapor lock first. Then put fuse in and start it up. Thanks again to @BoxCarKidd for talking me through that ordeal. Explaining how all that works. Ran it home, before it completely blew the gasket.

 

What year and make is the Truck?

 

When running, compession is keeping the majority of coolant out of the cylinder, and what little does get it goes right out the exhaust.

Shut off hot, cooling system pressure pushes it into the cylinder. Hot start, the coolant hasn't had time to seep past the rings. Cold start, coolant has already made it to the pan besides whats in the dish

 

Ok