Attention: TDR Forum Junkies 
I worked for a pretty large private service in Chicago, (Vandenburg Ambulance) and worked the night shift. We used to "stage" at strategic places throughout the city in what was then termed "status system management". We would find ourselves oftentimes on the lake front waiting for the next call. Those old 6. 9's and early 7. 3's would not maintain any temperature when the -20 windchill was screaming off the lake. And yes, there was no shutting them down!
Oh the memories you bring back
I remember a couple slow nights being out there and trying to catch a snooze in the back of the ambulance being around 30 degrees inside. Made for some long nights! Quickly learned that thermal underwear was my friend.
But yes, if they had oil in them at the start of the shift, they would make it through the night. They were pretty tough motors for what they were asked to do. The only real problem we had back then was transmissions. I remember the mechanic saying we were only getting about 15k miles out of a transmission rebuild. That might have had something to do with having a bunch of 20 something kids driving them though
For what it is worth, I do know the top speed of an IDI 7. 3 in a type II, (van). 107mph as clocked via the Illinois State Troopers. That was enroute to a particularly bad crash on I-80. I am strangely surprised sometimes that I am here typing stuff such as this and lived through those early years... .
When I first started, I would work 2 12's and one 24 per week and then catch an additional shift or 2 when someone called off. It was nothing to end up with 70-80 hours at any given time. Of course, when you are 20, you don't need sleep. Now, I have trouble making it through one long day. I started at 7:45 yesterday and didn't get home until after 11:00 last night. Just rolled my lazy middle aged butt out of bed after 8:00 and I'm still chugging down coffee just trying to get going. :-laf
Getting back to those old units for a minute, back during the blizzard of '93, I believe that we worked something like 3 or 4 days strait. After the snow stopped the temp dropped to well below 0 not factoring the wind chill. I know that those old Fords ran for at least a week never shutting down. When we were out on what we call "halfway standby" which would be your status system management, I would go out a drape a tarp over the grill just to try and keep a little heat in the thing. After a few years, I got smart enough to halfway in the parking lot of a convinence store or other local business so that we could at least have a place to go and get warm.
I don't run the units much anymore, but speaking of top speed, I've heard that a 2013 DT466 Int. is ECM limited to 84 mph and gets about 4 mpg doing it.
