In the early 80's, we ran an experiment with a fleet of fishbowls, 6V-71 engines. Answer was two gallons per hour. Wilmington DE, outside storage, winter. On cold nights, we had to let the fleet run (fast idle, of course), or they wouldn't start in the morning. I don't remember whether we were trying to find whether wiring the yard for block heaters would be cost-effective, or if it was to help me spec new buses. Or, it could have been just because we wanted to know -- I don't remember.
However, that information helped me decide to equip the 55 new buses we were going to buy with Webastos. Ended up with RTS-04's, equipped with 6V92 TA's, but I got promoted and transferred to another property before we had much experience with them. You know you're getting old when you can remember buying brand new buses, and realize they've been long in the junkyard, as has been their replacements, their replacements, and maybe their replacements.
Arthur