Now I'm pretty certain this wasn't intended, but it turns out with the recent change to Fission, a vehicle with a Fission engine will heat up while it's not moving. Once a vehicle with Fission overheats, the only way to cooldown to a non-overheated state is to leave the vehicle until it's started to cooldown.
It was intended because I tested if you could overheat it 100%, then still move (I added biodiesel qualities) to fire up the cooling again. In testing, that worked. If it doesn't now then I'm a little confused.
It worked in 2.40 too, the thing is its acceleration is almost non-existent. So unless you overheat while already moving you'll take a beating before you start moving because you simply won't move away. And if you're in a pothole/ on a sloped area, you're in serious trouble.
The bio-properties were meant to be a really gimped version of it. I.e. enough to let you move at like 10mph until your heat comes down.
You go at <1 if you try to start moving from a standstill. You can keep any speed you had before you overheated, but barely, if at all, accelerate.
The heating up while not moving, if that was intended, then sorry for bothering you. But then the problem is that the cooling system doesn't kick in once you're overheated for a good amount of time. It's safer for me to jump out of my tank for a full five seconds so it can start cooling than for me to try and move once it's overheated. It still moves with the incredibly low acceleration, but because of the low speed and inability to fire a weapon, coupled with the added heat from being shot at, becomes fairly useless when it overheats.
Yeah, something isn't working as intended. Given the issue with Bush, and the fact that I'm waiting for a small fix on Crossroads, I'll try and fix it, and throw it in a small 2.42 patch in a week or so.