They don't put kids in that tow truck bus. You sit and wait for another yellow bus to come get you. I don't know why they made that tow bus--I assume it is owned by the school district from the lettering on it. Must have been cheaper to just buy the wrecker kit than a whole wrecker.
If that wrecker-bus smokes badly, maybe they took the turbo off and didn't reduce the pump setting. Or, more likely, the thing mostly sits around, it's got some injector issues and the required fine mist of fuel is instead a bunch of dribbles that don't burn very well. Black smoke is simply overfueling or incomplete combustion. A little black smoke is okay because it shows you are using all of your available air. A lot is just for show. If you don't have a turbocharger, don't muck with the pump setting. Naturally aspirated motors run really hot as it is. It's the opposite of a gas engine where fuel cools the motor. Going down the road with 3psi of boost, the motor is running 300F cooler EGTs than naturally aspirated--at the same power.
I have limited farm tractor experience (gas JD 4020 w/ dual rears) but I have disced a field. There are no downhills pulling a 12' disc. That fukcer is going 100% the whole way for hours and hours at a time. A truck doesn't have that need--it needs a lot more power for short bursts, but runs along at 50% most of the time.
