The Car Doc on cold weather and tire pressure, extended oil changes and more

John Paul, aka “the Car Doctor,’’ answers readers’ car-related questions.

By John Paul @johnfpaul

August 16, 2016

3 minutes to read

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Q. Last winter, the tire pressure in my 2012 Lexus ES would decrease in the cold weather and the pressure light would come on and I would put air in the tire. This happened several times over the winter and spring. I took it to the dealer and a tire store and they found nothing wrong. This May I replaced caps on the valves and it has not been a problem. Can tire valves leak and the cap be the fix?

A. Cold weather does have an effect on air pressure. The typical passenger car tire will lose about one pound of pressure for each 10 degree drop in air temperature. Regarding the valve stem cap, you are correct it is actually the cap that seals the air in the tire. The Schrader valve in the valve stem allow for easy inflation. I would suspect it is a combination of better sealing valve caps, warmer weather and vigilant tire maintenance is the answer.

Q. I read in a previous column about problem with Toyota RAV4 steering, I am considering buying an 8-10 year old RAV for a winter “beater’’. What is the chance of a RAV needing an expensive steering repair?

A. There is a Toyota technical service bulletin about a fix for a clunk pop or knock-type noise when turning the steering wheel. The repair is replacement of the steering intermediate shaft. Prior to buying the vehicle have a complete inspection performed. As good as Toyota vehicles can be, you are still looking at a 8-10 year old vehicle that can suffer from numerous issues.

Q. I have a new GMC van that I use for my carpentry business. Like I did with all my vehicles I brought the truck in for an oil change at 3,500 miles and the dealer said they would change the oil but it didn’t really need it. They said the best thing to do was follow the oil like indicator and when the reading gets down to 10 percent life bring the truck in. I am not comfortable waiting for 5-7,000 miles before changing the oil. In your opinion, what is the correct procedure?

A. GM believes that extended oil changes help reduce owner’s costs and are better for the environment. In fact at one time GM issued a bulletin to its dealers that stated: If all GM customers with GM Oil Life System equipped vehicles would use the system as intended, an estimated 100 million gallons of oil could be saved annually. If you are carrying heavy loads, towing a trailer or just generally working your truck hard, follow the severe maintenance schedule. That schedule recommends oil changes every 3000 miles. This would also give you a little buffer if you become a little lazy with your vehicle maintenance.

Q. A read an article that you wrote about TopTier gasoline and found it interesting. A couple of things I wasn’t sure about. Can a gasoline be as good as this TopTier gas and is TopTier gas just the premium grade?

A. TopTier gasoline as additional additive (more than mandated by regulations) that helps reduce harmful deposits in the engine. There may be fuel blended that meet or exceed the TopTier standards that have not for one reason or another decided to join the TopTier group. If the fuel is TopTier it must be blended across all grades. Fr more information on TopTier go to www.toptiergas.com

Q. I’m thinking of a small luxury car and I am looking at the Audi A4, BMW 2 series and the Mercedes Benz CLA and leaning toward the Mercedes. What are your thoughts on these cars?

A. In the spirit of full disclosure I have yet to drive the new BMW 2 series, although based on my past experience with BMW I would expect, great handling and performance.. I have always liked the Audi A4 it just is a good mix of ride, interior quality, design and handling. The Mercedes CLA, which I just had the opportunity to road test is a bit of a mixed bag. The styling is polarizing; you either love it or hate it the four-door coupe design. The handling is good, but the ride is a bit harsh. The fuel economy is very good, but it does require premium. The rear seating area is cramped and almost unusable it there is a tall driver and front seat passenger. I would rate the Audi A4 as my top choice.