Questions and Answers

Is Engine Idling Damaging Your Engine? Q. Hi Vincent, I have a question for you. I have an automatic car. I would like to know if a car engine will be damaged in any way if I turn on the car, the air conditioner is on, the car is on the parking gear but not move the car for a good ten minutes.

The reason why I'm asking this question is that I hear from my friends that starting the car but not moving it will cause petrol and engine fluids to gather at the engine and that it is damaging to the car. Can you confirm if this is true and if there are any damages done indirectly to the car engine when I start it, turn on the A/C, keep it on parking gear, without moving the car?

Thanks,
Ryan

A. Extended periods of idling will effect the engine, but not for the reasons your friends claim. The engine fluids, gas, oil anti-freeze will circulate through the engine as designed sitting at idle for one minute, one hour or one day. They will not, and can not, accumulate anywhere in the engine.

Engine idling does have a couple of effects on the engine, the most severe is to the connecting rod bearings. Because of the relatively slow speed of the engine, more pressure is exerted on the bottom center and top center of the bearings. The faster the engine turns, the load gets spread out more evenly over the bearing surface.

Prime vehicles for this kind of damage is police cars. Police cars spend an inordinate amount of time idling writing tickets, filling out reports and stake outs. I have replaced many a connecting rod bearing in police car engines because of this.

The other effect is not so drastic. It is an idling engine may not get hot enough to start the catalytic convert working or hot enough to run efficiently. It may also load up the catalytic converter with fuel that could lead to an early demise of the catalytic converter.

Do you have to worry about this? Unless all you do is run your engine at idle, yes. But if you sit in the line at the McDonalds drive through for 10 or 15 minutes, no. You don't have to worry about it.