There are 2 things we know in the original Spintires. When you drive far away from an idling truck, or you change to another truck far away, the idling truck will turn itself automatically. The next thing we know is that they don't consume fuel when idling.
I'd like to see that change, at least in Hardcore mode. So trucks doesn't shut off when you get too far away, and they use fuel. So you forgot to shut off one of the trucks and you drove away to do stuff. Later you come back to a truck that has ran out of fuel, and now you have to figure out a way to put fuel in it.
Some may say this is very unforgiving, but I think that's what Hardcore mode is about! Spintires is a pretty hardcore game, and I think a small detail will add to it. If someone thinks you can drift your LaFerrari at 200km/h through mud they're looking at the wrong game anyway.