CLICK & CLACK : Savings vs. Safety

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Sunday, May 31, 2009

Dear Tom and Ray:

This past winter, my husband and I had a discussion about the rear defrost in our Buick Century. He rarely uses it and tried to convince me that the rear defrost is one of the biggest energy guzzlers in the car (as compared with the radio, heater, etc.), so he tends to turn it off as soon as he can see out a little. I contest that visibility should be more important than energy use. Does the rear defrost use more power/energy than most of the car's other standard features? -- Kari

RAY: It uses a small amount of electricity, Kari. And anything that uses electricity does impose an additional load on the engine, which costs you some fuel.

TOM: We don't know what your particular rear defroster uses, in terms of amps. But it's probably somewhere between the radio and the headlights. At worst, it's comparable to your headlights. Using your headlights may decrease your fuel economy by about 1 percent.

RAY: But your headlights are on for your entire nighttime drive. The rear defroster runs for about 10 minutes, then automatically shuts off. So they're not really equivalent.

TOM: Nonetheless, he's risking your safety to get 20.5 miles per gallon instead of 20.3.

RAY: Tell him that if he really wants to save money, he needs to stop using those energy-hogging headlights at night.

Dear Tom and Ray:

Our 2000 Saturn sedan has died twice in the same spot (at the end of a highway exit ramp). The first time, it took 10 minutes or so to get going again; 30-40 minutes the second time. Then it happened on a straight stretch when slowing at a stoplight. An engine scan showed a torque converter solenoid problem, but the mechanic does not think this is the problem. Could it be a fuel pressure regulator? -- Jim

TOM: I think it probably is the torque converter solenoid.

RAY: Modern automatic transmissions have a device called a lock-up torque converter that improves your fuel economy. Normally, in an automatic transmission, power is transmitted through the "automatic transmission fluid."

TOM: By using a viscous fluid to transmit power from the engine to the wheels, the transmission allows for some "slippage." That way, the engine can keep running even while the wheels are stopped (like when you're at a red light).


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