Hello Hugh. I agree with this fellow that you should turn the engine off when you're replacing the fan belts. You should also turn it off when doing the following: when changing the oil, when disconnecting the power steering high pressure hose, when removing the heater, when popping the top on your distributor, when there are any animals inside the engine compartment, and when inside a closed garage. I hope these tips help. Bye for now. Doug 58 Crown coupe