In real life I've never seen a car crash and then the cars exploded... but in arma I have, but that's okay and cool. But however i think the vehichles should begin to burn before they just exploded with unrealisticly little warning. Add some smoke coming out the engine and fire, the fire causes the last damage needed to make the vehichle explode and grilling the crew inside.
So: Damage-->Smoke-->exposed fire-->buummmm.--> vehichle burning out. <-- realistic
Instead of: Damage-->whatthefu-boooommmm. <-- unrealistic