The first car I ever owned didn’t have power anything. Today you will be hard pressed to find a car without power brakes and steering. But those features also consume energy. This explains how the first wave of economy cars from Japan got such notoriously high mileage (they didn’t have power anything either).

One reason I chose a Yaris for my next car is that it has electric power steering and power brakes. In theory, you should be able to turn the engine off without losing power boost. I asked a mechanic at the dealership before I bought the Yaris if the power steering and brakes would continue to function with the engine turned off. “No, no,” he said definitively. “It’s just like any other car.”

Surprise! The mechanic didn’t know what he was talking about. I’ve turned the Yaris engine off several times now while going downhill and the power boost systems continue to function just fine. Don’t try this at home.

[update] Seriously, don’t try this at home. The mechanic was partially right. I’ve discovered that, given enough time, the brake boost system will eventually depressurize leaving you with insufficient braking at the bottom of a long hill. The Toyota engineers left power boost running just long enough to get you out of a pickle in the event of inadvertent engine shutdown.

I found it hard to believe that Toyota engineers would turn off the electric motors that could run on battery power just because the engine died. It would be a no-brainer to keep the power brakes and steering alive for safety reasons.

I’ll be able to turn it off by pushing a button and start it again by pushing another without losing power steering and brakes. Turning an engine off does not always save gas. It takes extra gas to start an engine and extra energy to charge the battery back up after it is used to turn the starter. A general rule of thumb is that you will come out ahead if your engine is off for 30 or more seconds. I’m going to experiment with this switch setup to see what it does to my mileage. I sometimes haul a carpool of kids to a school at the top of Capitol Hill across town. Coming home is downhill all the way. I should be able to keep the engine off for much of the trip.

I should also be able to recoup some of the energy lost charging the battery. When I put the car in neutral, the engine rpm increases noticeably. This means that the Yaris automatic transmission is drawing significant power from an idling engine when stopped at a light. I might as well capture some of this in the battery, which will be used pretty hard, by putting the car in neutral as often as possible when the engine is idling. There is a chance that I can drain and therefore ruin the battery by using it to power the boost system.

All cars already have a heavy electric motor that they haul around for occasional use. It’s called a starter. Some pseudo-hybrid car designs are already automatically turning the engine off at stops to increase gas mileage and have modified the starter motor and increased the size of the battery to get the car rolling and to restart the engine. They also use some regenerative braking to keep the battery topped off.

I have a similar goal, except I intend to bring along some grid-charged batteries. All I need is enough electrical power to get the car rolling from a dead stop in stop-and-go traffic, or to keep it rolling on level ground at low speeds. It would not be used to shove me up big hills or exceed 30 mph. I have no illusions of using the Yaris starter motor for this. I’m thinking along the lines of modifying a small trailer that can nudge the car along on short in-city trips and be unhitched for other trips. Why haul a motor and batteries around when you don’t need them?

The Yaris appears to have a sophisticated starter solenoid already in place. Close the circuit to it for a fraction of a second and it takes over, starting the engine for you. Old starter solenoids required the driver to keep the switch closed until they determined that the engine wouldn’t die. These discoveries make me suspect that Toyota is contemplating a hybrid version of this car.

Certainly, the Prius somehow knows when to start and then starts its engine. I’m not sure cars should be that smart. Call me paranoid, but I suspect they may be self-aware. I also don’t like the way they stare at me.