Ha! Funny you should mention that. When I filled it up in the ditch and started it, I thought the heater core blew out because I heard a a whoosh and running water in the heater core for a second. It was definitely nose up.
I don't know the criteria, but according to the owner's manual - when an overheat is present , it will alternate pairs of 4 cylinders. When it gets really hot, it will shut the engine off completely.
Insurance on medium duty trucks can be a bit on the high side and I'd want something pre-emissions if it's a diesel. But 6.0L gas powered Isuzus do get a second look on FB Marketplace and CL. Possibly E-350s but apparently 4.6 and 5.4L powered van/wagons have the same 4R70/5 transmission as my grand marquis or a F-150. Not sure how I feel about that trans for my use. However, friends of mine who are mechanics rarely if ever do transmissions in E-series vans but apparently frequently in the GM vans.