Doing a story on the D364 diesel electric set installed 1952 into SS Col. James M. Schoonmaker (launched 1911 and now a museum boat in Toledo at the Museum of the Great Lakes). It's a bit of a hybrid in that it used a radiator rather than being raw water cooled with a heat exchanger. Anyway a few questions:

RE hour meters on the D364 and similar engines in this era. I am working with the museum on this. The hour meter is difficult to read. It appears to be a four digit meter but the current Chief Engineer of the boat went in to have another look for me and he swears there is a fifth digit off to the right. He's not sure if it is tenths or not. I have only seen (what I thought to be) four digit meters, and I think three. What do you guys say?

The D364 was a long running engine ('49-56). The venues in which I see it used include as marine power, power units and generators. Were they ever used in construction equipment or vehicles of any kind?

Here is a pic of the engine. It hasn't run since around 1980 and will never run again by edict. It's rated at 150KW, 450 volts AC, 203 hp @ 1200. It was a bit of a special build. Kent Bates is trying to find the BOM but hasn't been able to at this point.

 

That's a very interesting power plant and electric drive in a ship.

I don't believe the ship is electric drive. That appears to be the ships generator.
The D364 arrangements are:
19Bxxxx = Industrial Engine
20Bxxxx = Marine Engine
21Bxxxx = Diesel Electric Set
I don't believe they were used in any vehicular applications.

The boat's main plant is steam, as are the main generators. The Cat is a standby unit or for electrical  power when the boilers are cold and the steam generators down. According to many sources, the generator was most often used when the boat was being prepared for winter lay-up and for bringing the boat back to life in the spring. If the boat was going to be tied up for more than a couple of days, they might shut the boiler down to save fuel and run the diesel instead. One of the charts I found show this engine as using abut 15 GPH with a full load... and that's pretty decent. Probably a lot less than keeping enough steam up to run the steam generators. And less crew needed as well.

Kent gave me the build date of the engine, 1951, and it was installed in 1952 during a major refit (recip steam replaced by steam turbine). What I find most interesting is the choice of a radiator versus more typical marine raw water cooling. No doubt a cost saving choice, given the way it was planned to be used. Still, in the files of work orders for this engine, some discuss overheating issues. In one, the tech cited 127F ambient operating temps ( : < 0) as being a contributing factor... obviously referring to the generator running with the boilers lit and the engine room hot. Yeah... I can see that as a potential problem ( : < ). That's where raw water cooling would have been a saving grace.

The other diesel generator, a much smaller US Diesel  50KW DC unit , was installed in 1947 mainly to power a new electric hatch crane, is down low and maybe runs cooler. It was installed mainly to running an electric hatch crane but they also installed a DC-to-AC motor generator to provide some shipboard power. It's also radiator cooled. I did  story on the smaller generator some time back, which also has some extra history on the boat. You can read it here: Unsung Hero

Could also be the area where the unit was sited. That's assuming, I guess, that the Cat tech accurately reported the facts. I saw lots of ventilation down there generally speaking, as you would expect. There were a number of work orders regarding overheating and some that suggested radiator core replacement.

It was similar to the standard D364 21B package, but with some differences. I found references that standard marine raw water cooling could be added to a build if desired. The generator head is a marine unit, and it's downrated a little from the standard "outta-the-box" 21B D364 diesel electric unit, which was rated at 165 KW and 215 hp. So it was a custom build to a degree. Kent has looked for the BOM and maybe he will have time to find it. That will tell the tale. It's definitely not the standard advertised D364 21B set.

Can anyone offer clues about my hour meter question?

They were five digits, tenths would have no white background.