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Transmission warm-up helpful in some cases

| Saturday, Jan. 9, 2010

Question: I see lots of advice on how long to warm up a car's engine in cold weather. But doesn't the automatic transmission require a warm-up as well• In below-zero weather I've had cars barely run or shift until the fluid warms up and flows better. Isn't that a consideration for how long to warm up a car before driving it?

Answer: Yes, it is. When temperatures are tolerable to us humans -- perhaps 20 degrees and above -- not much warm-up is necessary for the automobile. Start the engine, allow it to stabilize and idle for perhaps 15 seconds, shift into gear, wait a few seconds for the transmission to fully engage then drive the vehicle up to temperature gently.

There are valid reasons for longer warm-ups in moderate conditions -- age and medical condition of the occupants and age and mechanical condition of the automobile. In any case, if the vehicle is in the garage, back out into open air before warming it up.

The faster we can warm up the vehicle, the more efficiently it operates and the less fuel it consumes and the fewer emissions it produces. The key is bringing the catalytic converter up to working temperature as quickly as possible. Driving the vehicle under moderate loads accelerates this process.

The game changes somewhat when temperatures drop into the "uncomfortable" or "extreme" range -- typically around 10 degrees and lower. Engine and transmission fluids are more viscous, or thicker, in these conditions and resist pumping, meaning it takes more time and energy to get these lubricants flowing to critical parts.

So, when it's extremely cold outside, start the engine, and let it idle for a minute or so before putting it in gear or under load. This allows engine oil and transmission fluid to circulate and lubricate. Then shift into gear and let the engine and transmission warm another 30 to 60 seconds. The "light load" generated by engaging the torque converter and transmission will expedite the warm-up process.

Perhaps the simplest and most convenient method to deal with cold starts -- assuming your vehicle is parked outside and not in a garage -- is an autostart system. Hit the button from inside your home or office and let the vehicle warm up a bit before you head outside. Leave the heater and seat heaters, if you have them, turned on when you park the vehicle so they'll come on and pre-heat the cabin and seats before you slide behind the wheel.

Q: How do you view trade-offs of safety features• Should I buy a used '08 Ford Escape with disc brakes but no stability or traction control• Or the '09, which has stability control but drum brakes?

A: I'd choose traction/stability control. The issue of four-wheel disc vs. disc/drum brakes is, in my opinion, not particularly critical because the front brakes -- discs on both vehicles -- do most of the braking. Traction/stability control, like ABS, is a passive system that does nothing until you, the driver, make a mistake by asking the tires to deliver more traction than conditions permit. Then these systems modulate, adjust or reduce the forces applied to the tires to keep the tire working within its traction envelope. Doing so gives the driver the opportunity to fix the problem before losing control of the vehicle -- always a good thing.

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