Q: Could you please bring me up to speed on the different oils now used in car engines? The oil fill cap on my new Buick reads Dexos 5W-30 whereas my 2002 Bravada oil cap read just 5W-30. The Bravada has 78,000 miles on it. Because of the low annual mileage I've been changing oil every 4,000-5,000 miles with the "oil life" monitor indicating 20 percent remaining. This April I checked the remaining oil life with only 1,000 miles on the oil. It read 46 percent. At 2,000 miles on the oil it read 21 percent. I have a feeling the dealer may have used Dexos oil instead of conventional oil. If so, can I change back?
A: "Dexos" is a license GM offers to oil companies who produce a lubricant meeting GM's strict standards. It is not a different type of oil and would not be the cause for the more rapid reduction in remaining oil life. The oil life monitoring system does not know what type of oil is in the crankcase. It does monitor engine starts, running time, coolant and oil temperatures, rpm, throttle setting, manifold pressure, etc., to compute how hard the engine is "working" the oil. From this data the system calculates when the oil should be changed.
Back to the Dexos standard. Many oil companies are paying GM to carry the Dexos symbol and blending their oils to meet GM standards. These standards are high enough to require the oil to be semi- or full synthetic rather than conventional petroleum oil. Switching from Dexos to non-Dexos-licensed oil in your older Bravada will not damage anything as long as the oil you choose meets the proper API service rating — currently SM for gas engines. But why do so? The Dexos-licensed oil is required for your new Buick and is the highest-specification oil available.
Dexos-licensed oils are available from most major oil companies, including Valvoline, Mobil, Havoline, Pennzoil, Castrol and Quaker State.
Q: I own a 2001 Camaro. The past few months the radio and power windows will go out, then work again a few minutes later. Should I have this fixed — if affordable? Other than being annoying will it be all right to keep driving the car?
A: Since both the radio and power windows are controlled by the BCM (body control module) and its RAP (retained accessory power) relay, the intermittent operation may well be a poor BCM harness connection. Replacing the BCM would be expensive, but checking the connectors at the BCM — located behind the right side of the instrument panel — would be simple and inexpensive.
Q: I have a friend who is storing a Mustang for someone and is using a charger to maintain the battery in the car.
He gets $50 a month for storing the car and it costs him $30 in electricity to maintain the battery.
