I’ve heard that diesel coolant systems aren’t really all that watertight and coolant water could end up in the lube soil, and that glycol in the bearings is fatal. I assume that a little water in the oil could be managed, but not glycol. Plus, as noted, it’s expensive, it’s toxic, and diesels constantly need a cooling water ‘top up’ and it would be hard to keep an accurate record of the water/glycol ratio. I’ve also read accounts of engines breaking down, or derailing, or cases of fuel starvation out on the line in the winter where the crew would have to find the energy to drain the coolant system of the shut down engines before calling it a day. Can you imagine: you’ve just plowed into the weeds and now you need to crawl into the mess to drain the engines, at 30 below, in the dark?!
Geoff