If one is traveling 60-70 mph on the highway, turns the engine off and restarts the vehicle (several times per week)… will this cause damage to the transmission?
Why in the world would you want to do such a thing? You are not going to increase the mileage enough to offset possible damage. In fact I doubt even if it had no chance of damage, how it would be worth the bother.
Did you know that some cars will do this for you automatically and safely.
One will not live long enough to care about the transmission. Sooner rather than later the lack of power steering and power brakes will simply wreck the vehicle and its passengers.
You are not saving fuel. You are wearing out the starter and battery as well as endangering the life of yourself and your passengers. Bad idea. The damage to the transmission should be the last of your worries.
I would also like to know why this person is doing this. The answer to your question is YES, it can damage an automatic transmission. When you shut off your engine with an automatic transmission you are also shutting off the pump inside the trans. The job of the oil pump in an auto trans is not just providing hydraulic pressure to apply friction elements but it also provides lubrication to the rest of the transmission (Bearings, bushings, gears etc.) All those things are still turning as long as the drive wheels are turning, and at 70mph??? A quick way to destroy a transmission SO, if YOU are doing this, you need to STOP doing it immediately.
Transman is right. This will cook an automatic transmission, and probably won’t take long to do so. This is basically the same as towing an automatic with the driven wheels on the ground. Even in neutral, you are still moving a lot of parts which are not getting any lubrication from the fluid since the engine is not running. If this is some sort of fuel saving measure, it will prove to be an expensive one.
If you read your owners manual it likely says that you should not tow your vehicle with the wheels on the ground. That is because it will damage the transmission. Transman has explained why the damage occurs.
This is a dangerous practice. It has no value, and it hurts the car. Why do it? If you think you are saving some gas, you are mistaken.
Back in 1950, we lived about 3 miles from the Borg-Warner plant that designed and built the automatic transmissions used by Ford and Mercury. We would see a Ford or Mercury come past the house about 60 miles per hour and the driver would shut off the engine and coast almost to a stop and restart the engine. Sometimes the car would make a lot of noise and come to a stop and go shooting backward. I was in elementary school at the time and didn’t know what was going on except that someone was being very hard on a brand new car. I found out later that test drivers were seeing how much abuse the transmission could take. These automatic transmissions were introduced in the 1951 Ford and Mercury cars. The test cars were 1950 Fords and Mercurys fitted with the prototype automatic transmissions. I don’t think that the OP is a test driver trying to test a transmission for stress factors.