In the unlikely event of an engine bay fire after a crash, an explosion as was shown would not take place. Cars burn at a fairly slow rate, and the only way an explosion would take place is if the fuel tank was nearly empty. This error takes place regularly as it is widely used for entertainment purposes.
When the police car windshield is shot by the shotgun, it is clearly special glass (called candy glass used in movie props) that shatters. Car windshields are made of laminated safety glass and do not shatter as shown.
After Gordie Hobbs side sweeps Eddie Pearls car and completely rips both passenger side doors of he proceeds to ram the car at full speed several times. Later at the motel where he is staying the jeep is there and has no damage whatsoever.
When Decker's car crashes the hood is up revealing a fire that has started for no apparent reason in the engine compartment. In the next scene the hood is down. Then just before the car explodes three times the hood is up again.
When Hooker starts "chest compressions" on Gordie he presses several inches too low, over Gordie's stomach.