I'd bet they use a glycol based coolant -- if not, not only will they freeze, but the coolling system will not work very well. Dont' know for sure, but a full anticorrosion system is necessary, and unpressurized cooling systems aren't worth much.

No need to save weight in a locomotive, quite the opposite (normal weight is in the 750,000 lb range), but I do know that not all of them are in use every day, nor continuously, and dumping the anticorrosion fluid all the time in the winter is wasteful.

Marine diesels may or may not be directly cooled. WWII diesel US subs are simply railroad locomotive packages, but probably had indirect cooling -- seawater would cause too much trouble (corrosion and the possiblity of salt accumulation if overheated).

The ability of the US to drop a well known and well developed train genset into the subs was a distinct advantage -- they performed beautifully, and having been developed for moneymaking companies, weren't prone to having weird parts or excessive maintenance requirements. The German sub engines, while very good, were considerably more tempermental. Open rockers on those, by the way -- must have made for VERY messy engine rooms!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!