Motormouth: How often do I really need an oil change?
Q: I have 2001 Lexus RX300 with only 46,000 miles. I bought it new and have kept it in mint condition. In recent years, I have only put on 1,000 miles per year and have switched to a once-a-year oil change. I know the "law books" say you should change oil every six months, but I have also read a lot of commentary that you can go much longer than a year depending on how you use the car and mileage. In your opinion, is once a year OK?
— D.E., Naperville, Ill.
A: Oil change intervals have changed from 3,000 miles/3 months, then to 7,500 miles/12 months, and now to whenever the warning appears on the instrument panel. But if your 1,000 annual miles are all due to short trips, I suggest you change the oil and filter at least once a year. Short hops do not allow the engine and oil to get hot enough to cook off any moisture that may have condensed in the crankcase.
Q: Can you recommend a good and reliable heavy-duty portable tire inflator? I need one that is strong and powerful enough to be able to add air to my Titan pickup tires. The one I have is OK for the smaller tires on my Kona and Soul and bicycle tires but it struggles with airing up the Titan tires.
— D.S., Georgetown, Texas
A: I have not personally used a 12-volt compressor in the 100-psi range, but there are plenty out there. Many Titan pickups also have power inverters that provide 120 volts AC power, usually one in the cabin and another in the truck bed. More power to you.
Q: How does one know what grade of gas he's buying? I was buying gas at a top-tier gas station when a generic tanker truck pulled in and started filling up the storage tanks. Years ago, tanker trucks went to gas stations with the brand on the truck (Shell, Sunoco, BP, etc.); now all I see is generic. I asked the tanker driver about top-tier etc., and he said all gas at the tanker farms come out of the same storage tank, hence, it's all the same. Gas is gas. Who puts in the detergent additives in gas?
— D.C., The Villages, Fla.
A: Gasoline is a commodity shipped from major refineries by pipeline or ship to tank farms. Before that gas is shipped to the retail stations, it is blended by the marketers. Some even have fancy names for the additive package. Top-tier fuel has a better detergent package than the EPA requires and is worth seeking. A few companies have their own dedicated fleets of tanker trucks while many contract with various carriers.
Q: Before a recent 600-mile trip, I checked my tire pressure and all four were at the recommended cold tire pressure of 35 psi. The dashboard monitors also indicated the same readings. About 1 1/2 hours into the trip (it was a hot day), the tire pressure light on the dashboard lit up. I checked the info center and saw that all four tire pressures were now at 37 psi. Is this something that I should be concerned with? They are original tires (only 39,000 miles on them).
— J.A., Cetronia, Pa.
A: Tires flex as you drive and flexing causes friction, and heat. The air pressure then goes up. We check our tires cold to provide the best baseline reading. Warm tire pressures vary. You may ignore common increases in pressure.
(Bob Weber is a writer and mechanic who became an ASE-certified Master Automobile Technician in 1976. He maintains this status by seeking certification every five years. Weber's work appears in professional trade magazines and other consumer publications. His writing also appears in automotive trade publications, Consumer Guide and Consumers Digest.)
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