Dear Tom and Ray: While I was attending the University of Oklahoma in 1960, a study was done by the petroleum engineering department. The question was: Is draining oil from a vehicle necessary? They worked with White Trucking Co. and tested their theory on long-haul trucks. Using only a "toilet paper" filter and only adding oil, they ran one set of trucks against ones that received oil and filter changes for 100,000 miles. The results showed no significant wear differences between the two. They also concluded that the oil in the no-change vehicle was "stronger," because the weak molecules in the oil broke down and evaporated away. This study was going on at about the time that the Conoco Oil company was working on biofuel and had developed a plant in Bartlesville, Okla. But then both the study and the plant were suddenly gone, and I never heard any more. What is your take on the oil-change theory?
Tom: Ah, yes. I remember that study, Don. It was funded by Charmin.
Ray: Actually, while we don't know anything about that particular study, I'd take it with a grain of salt.
Tom: First of all, motor oil has improved dramatically in the past 50 years. So whatever was done then probably doesn't apply now.
Ray: Also, long-haul, diesel trucking engines are built to last much longer than automobile engines. So 100,000 miles might not have been enough to show the damage of forgoing oil changes.
Tom: We have heard about the toilet-paper filter, though. It's called a Frantz Filter, and it has had a small cult following throughout the years. As you might expect, you install the housing, and then you simply stick a roll of 1,000-sheet, two-ply, 100-grit toilet paper in the holder, and that does the filtering. When it's dirty, you remove it and insert another roll.
Ray: It's not a surprise to us that it never caught on in big numbers, because it requires men to change a roll of toilet paper.
Tom: Aside from that fatal flaw, we've had good reports about it from our customers during the years. But keep in mind that anyone who would go through the trouble of installing and using one of these things obviously is interested in car care and maintenance. That kind of person probably tends to take particularly good care of his car in all kinds of other ways, which could skew the results.
Ray: In any case, Don, our personal experience at the garage suggests that changing the oil and filter regularly is good, and not changing the oil and filter regularly can be bad -- even catastrophic over the long haul.
Tom: And it's relatively cheap insurance. It's $20 or $30 a few times a year, for most people. So we still strongly believe in changing the oil in your car, and changing the toilet-paper roll in the bathroom. And not vice versa.
Dear Tom and Ray: I heard a caller on your show describe sitting in her car for 20 minutes while it idled so she could run her air conditioner and listen to her stereo. I couldn't have been the only one who cringed at that, could I? She was wasting money and fuel, generating pollution and, from what I've read, damaging her engine. Do you guys agree with this?
Ray: We've never condoned excessive idling, John. Except in the case of my brother.
Tom: Right. Sitting on a park bench with a cup of coffee during working hours is great, and I highly recommend it.
Ray: But as far as cars are concerned, you're right on three of your four points: It does waste money, it wastes fuel and it creates more pollution. But it doesn't really harm the car.
Tom: Right. With modern, fuel-injected engines and with computerized engine management, the fuel is metered precisely enough that excess fuel isn't pouring into the cylinders, like it was in the old days of carburetors.
Ray: Nonetheless, idling is still wasteful and selfish, and bad for the planet. So we recommend that if you're going to be stopped for more than a few minutes, you turn off your engine.
Tom: There's no harm in turning it off and on again. There's no truth to the myth that you "use more gas starting it than by letting it run." And you can listen to your car radio with the key in the accessory position.
Ray: One of the ways hybrid vehicles save fuel is by automatically turning off the engine whenever you come to a complete stop, even at traffic lights. And my guess is that sooner rather than later, all new vehicles will adopt this "automatic stop-start" technology. It's an easy and relatively inexpensive way to cut our national gasoline use by probably 10 percent, and make intersections smell a lot better.
Tom: But you can contribute today, even if you don't have that technology, just by being conscious of when your car is stopped for a few minutes. When it is, shut off the engine. Future generations -- and the poor guy sitting behind you -- will thank you.
Listen to "Car Talk" at 9 a.m. Saturdays and 5 p.m. Sundays on KRCU 90.9 FM -- Southeast Public Radio. Write to Tom and Ray at Car Talk Plaza, Box 3500 Harvard Square, Cambridge, Mass., 02238. Or e-mail them at the Car Talk section of cars.com.