I've got a Rhino, from the 3rd ed Blood Angels days, that never, ever passed an overcharged engines test. It always, and I mean always, broke down right in the field of fire. There's only one time this ever worked to my advantage.
So here was the plan: Get my squad of marines, with Mephiston, riding in Ol' Lucky, driving into a unit of fire warriors, through a small gap between two big rocks, prompt a tank shock, mop them up afterwards.
Here's the execution: Drive towards the fire warriors, until the engine sputters and dies. Disembark the squad, huddled behind the Rhino. There is about a two-inch gap between the back of the immobilised Rhino and the rocks, through which the models could squeeze.
The fire warriors opened, well, fire, on the rhino. They are, for the most part, mere inches away from it.
It exploded.
All the fire warriors die.
So do some of my men, but that's life.