Bluntly put? They do a lot of damage. It's probably not a good idea to attempt to throw oneself on such a grenade to save the rest of the unit, as it would appear that the grenades are perfectly capable of sending their victims- or their victims' parts- flying.

As for X's situation, what lies under the hood is an internal combustion engine of a sort. Whatever fuel it runs on, it's heavily based on alcohol rather than petroleum. It looks as if someone got hold of a Wankel rotary engine and forced it through fifty years of design evolution or more in the space of a week.

The APC driver chooses that moment to slam on the brakes, perhaps hoping to fling the unwelcome passenger from the hood and into the line of fire.