Automatics can't be roll started.

Dear Car Talk

Dear Car Talk | Jan 01, 1992

Dear Tom and Ray:

Can a car with an automatic transmission be started in gear by rolling? I had a 1981 Cadillac, and the starter failed in New Hampshire, at the top of the Kancamangus Highway. I was tempted to roll down this great big hill to start the car. Luckily, with the help of two young men, we got the car started by tapping the starter with a rock while I held the key on Start. But I'm wondering if I can roll start the car if this happens again.

TOM: Gee, Charles, if you DO decide to try it next time, call Columbia Pictures first so they can get a film crew out there. Those runaway mountain crash scenes are very expensive to film, and I'm sure they'd like to capture yours and use it in "Terminator III."

RAY: The fact is automatics can't be roll started, Charles. To start an internal combustion engine, you have to somehow get it turning. Once you turn it a few times, it should keep going by itself. Usually, the starter is what gets it turning. But if the starter fails, it's possible (although not recommended) to roll start a car if it has a manual transmission.

TOM: When you put a manual transmission car in gear, you mechanically connect the engine to the wheels. Then, if you roll the car, the wheels do what the starter does--they turn the engine and get it going.

RAY: But you can't do that with an automatic because there is no mechanical "clutch." Basically--and I'm simplifying this explanation so that my brother can follow along--the "clutch" in an automatic transmission is a fluid coupling, which only connects the engine to the wheels when the motor is running. So if you tried to roll start the car, the wheels would turn, but they wouldn't be connected to the engine.

TOM: We're confident that you would have figured this out after the first hundred yards or so. But to your horror, you also would have realized is that without the engine running, you have no power steering or power brakes. And in a 4,000 pound Sedan DeVille, that means a very quick ride to the gift shop at the base of the mountain.

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