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I was having a discussion today that turning off the engine while still moving along at about 20mph, while the engine is still revving will do no damage to the car, apart from the obvious safety issues (no brakes, speedo etc).

I think this is because the oil pump is still turning and the engine is being lubricated so it'll be fine to do this.

Am I wrong?

Will removing the ignition key while the engine is still turning damage my car?

What will happen if this did happen?

I obviously do not want to try it in case I destroy something and ruin my car or crash as I have no brakes in an emergency!

UPDATE: I have a manual transmission, fuel injected. I mean just turning the key to ignition, not actually removing it

George
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1 Answers1

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What will happen is dependent on the configuration of your vehicle.

Automatic transmission - Due to the torque converter, the engine will just stop. This is bad for the transmission, because the parts are moving, but the pump is not as the pump is run by the input shaft. This is similar to towing, where they typically recommend no more than 5 miles at no more than 25mph with the drive wheels on the ground.

Fuel injection with manual - If left in gear, engine will continue spin, but the injectors and spark plugs will not fire. Oil pump will keep everything lubed. As soon as you turn the key to ON again, it will run like normal.

Carb with manual - Similar to FI, except fuel will still be pushed through the engine. This is not good for wear, but will not cause immediate damage.

Also to consider, most vehicles lock the steering when the key is removed. The brakes usually have 1-2 presses left after the engine is shut off.

rpmerf
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