On the Cummins, coolant is used in the main heat exchanger where it is exchanged against raw water; the block, head and exhaust manifold; the turbine housing and maybe the fuel cooler.
The only one that might start leaking under a load of 1,500+ rpm is the turbo. The coolant might be leaking into the air side of the turbo. The air suction pressure drops under higher rpm’s and it may be sucking antifreeze into it. It would then have to be burned in the engine and you finally smell it in the exhaust.
Well, that’s my wild ass theory, FWIW.
David