Yeah, but don’t forget white smoke can also be incomplete combustion – as when glow plugs aren’t working, or when a DI engine is stone cold. Some of the FL9s as maintained by PC in the early '70s would produce the most amazing clouds of white smoke “accelerating” out of Harmon.
Watch the speed with which the white smoke dissipates, and the way the smoke moves. It’s different for water vapor than for unburned fuel. Remember that almost all locomotives don’t use Prestone or other antifreeze – the coolant is water. The amount that can leak into a locomotive-size compression-ignition engine without either quenching combustion or causing, ahem, worse problems like hydraulic lock shouldn’t be that likely to give massive amounts of visible water vapor out the exhaust…
In my own experience, an internal coolant leak is more likely to show as contamination of lube oil than abnormal exhaust smoke. The amounts of coolant (small) and the amount of heat in the cylinder and exhaust garuntees a clear vapor, unless the amount of coolant is very high. I have never seen this in a diesel engine though, vs. a gasoline engine, I imagine the pressures in a diesel engine being much higher cause the opposite - combustion gasses pressurizing the coolant system, and in fact this is what I have seen in diesel engines.
I once worked on an ancient 6-71, that every time you revved the engine, the radiator would blow. When the engine was stopped, the air box drains gushed coolant until the system ran out of water. I was amazed the engine never siezed from hydraulic lock with the amount of water coming out of the cylinders, but shure enough, it would run. I pulled the air box covers and saw all the water was coming from one cylinder. So, I pulled the head. The exhaust ports were dry and had no rust, also the valves showed no signs of contact with water, and there were no obvious cracks. This engine is a 71, so it has dry liners. No sign of leakage around the fire ring, and no rust or scale on the piston crown. I was stumped, so I took it to a machine shop to have it pressure tested - this was a job I did for some freinds on an old drill rig out in the middle of nowhere with minimum tools. The machine shop notified me that the injector tube had lost its seal, I later learned from a sage, that this is a common problem in old detroits.
At any rate, this case illustrates typical symptoms of a large coolant leak in a diesel engine. A coolant leak in a four stroke engine may show in the exhaust smoke because of intermittent cylinder pressure, unlike in a two stroke engine, but if the leak is in the cylinder head, again the coolant system will be pressurized. I have seen internal coolant leaks in other engines with wet liners, in those cases, the engine “pyucked” a lot a