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Cold-weather vehicle care

Answers on car warm-ups, batteries, and winter tire pressure.

Question: I've seen articles about warming up vehicles before driving in the winter. I understand that doing so makes problems for the environment and is not necessary - that the best way is to just drive off.

But what about folks who drive only three miles to work?

My 2008 Hyundai Sonata barely gets heat by the time I get to work if I don't at least let it run for a couple of minutes. By letting it run, I am allowing the natural moisture in the air in my engine to evaporate due to heat to prevent further problems down the road.

Is there any validity to allowing the moisture to evaporate?

Answer: Absolutely. Short drives in cold weather leave significant moisture condensed into water and not evaporated from the engine crankcase and exhaust system.

From a mechanical and environmental perspective, no significant stationary warm-up, idle period is necessary in winter. In fact, engines and components come up to temperature more quickly, producing better fuel economy and lower emissions, when driven gently up to temperature.

But there are two scenarios where an extended warm-up prior to driving is useful - at the start of a short drive, as you've described, or due to a medical/age necessity. Both are completely valid reasons to let a car warm up. It won't harm the vehicle.

One option for you is to plan a 20-minute drive at least once a week to completely evaporate any moisture from the engine and exhaust. That will help prolong the life of exhaust-system components and the positive crankcase ventilation system.

Q: Is it OK to store a car over the winter while connected to a battery tender with the battery not disconnected?

A: The benefit to leaving the battery connected is no loss of onboard computer memories - radio presets, seat position, HVAC settings, idle learn, etc. All these quickly reestablish once the vehicle is put back in service.

The only potential downside, in my opinion, is the risk of fire due to some type of electrical problem/short circuit.

Q: Is use of a 9-volt dry cell battery plugged into the cigarette lighter or charging outlet OK when changing the battery? Is it necessary?

A: Why bother? When power is reconnected, the computer systems relearn very quickly.

Q: My 2013 Chrysler minivan calls for 35 psi cold tire pressure. A week before Thanksgiving, I added air due to a large drop in temperature. I watched tire pressure increase from 35 psi to 45 psi as I drove south for the holiday. Back north the tire pressure was back to 35 psi.

I would like to know what rule of thumb one should use for an upper limit on tire pressure.

A: Having raced on high-performance street tires for decades, I can tell you there is no risk to a passenger car tire operating at even 50 psi. So, no worries.

The short period of higher cold tire pressures theoretically may cause a slightly higher wear rate on the center of the tread, but that is far less of a concern than operating the tire well below its specified pressure due to lower ambient air temperatures.

The rule of thumb is a 1- to 2-pound loss of pressure for every 10-degree drop in air temperature.

Remember, don't try to add air to a tire when temperatures are significantly below freezing. It's no fun to watch the tire go flat right in front of you as the tire valve freezes open.