Clearing up confusion about new oil-change feature

Dear Tom and Ray: I recently bought a Honda Fit. I love the car, and the dealer even gave me a few hundred dollars for my Metro. I really like the Fit and want to take care of it. The Fit has a feature that shows the oil usage as a percentage. Do you guys have any idea what this is measuring? The dealer told me I don't need to worry about changing the oil until it shows 20 percent. I want to make sure this car lasts at least 10 or 12 years. Is there any advantage to changing the oil at 50 percent? I am basically a cheapskate and don't want to waste oil, but want to get the maximum life out of the car. Your thoughts and insight would be great.

Stuart

Tom: Well, Stuart, the mileage interval -- which we've used to change our oil for generations -- is basically a guess. It says, If you change your oil every 7,500 miles (most manufacturers' recommendation), you should get the old oil out of there before it stops being effective.

Ray: But it's just an educated guess. It's a one-size-fits-all solution. So what Honda and others have done (actually, I think GM was the first to do this) is opt for a more high-tech and individualized way to estimate oil life.

Tom: We know that oil wear is directly related to the amount of use it gets and the temperature under which it operates. In your Honda Fit, the car's computer measures those things. It keeps track of the fluid temperatures and the number of revolutions of the crankshaft.

Ray: And then, based on an algorithm that Honda came up with, it determines when the oil really needs to be changed. The advantage of this is that you save money by not draining out perfectly good oil.

Tom: This, of course, assumes that Honda's system works as described and that the algorithm is good. But if we assume those things (Honda has a pretty good reputation for engineering), then they HAVE come up with a better system. It fine-tunes the oil-change interval based on your actual driving.

Ray: The Honda system gives you a reading of "oil life remaining." So when you first change the oil, it reads 100 percent. You're supposed to change the oil before the gauge reads 0 percent. Your dealer is recommending that you change it when it gets down to 20 percent, and I'd agree with that. By changing it when the computer thinks you've used up 80 percent of the oil's life, you're playing it safe and changing it too early rather than too late.

Tom: And until we have more years of experience with this system under our collective belts, it's probably better to err on the safe side, Stuart.

Dear Tom and Ray: If one anticipates stopping at 100 yards when the light ahead turns red, should one continue at speed and then press firmly one time when near the light to stop, should one intermittently and repetitively press firmly to slow down incrementally, or should one ride the brakes with light pressure, or coast to gradually slow down and then stop if the light remains red or accelerate if it turns green? Does it damage the brake lining or brake cylinders to coast with continuous light pressure or "ride the brakes"?

Gerald

Ray: When you see a red light 100 yards ahead, Gerald, the proper thing to do is take your foot off the accelerator, and start coasting to slow down. Continuing to accelerate once you see a red light ahead just wastes gas.

Tom: Then, when you're a reasonable distance from actually having to stop the car, apply the brakes gently so that, if possible, you come to a stop right at the light, without ever having to change the amount of pressure you put on the brake pedal.

Ray: In other words, if you push the brake pedal 25 percent of the way down, ideally, keeping it pressed 25 percent of the way down should bring you to a complete stop exactly where you want to stop. That means you've braked perfectly.

Tom: That's the ideal, anyway. Don't be afraid to adjust the brake pedal and push harder if you've estimated wrong! But in general, you want to brake as gently and smoothly as possible.

Ray: Why should you do it this way? So your passengers don't get carsick, or bump their heads on the dashboard.

Tom: It's also better for the car. When you brake suddenly, you put stress on lots of other components. For instance, you cause the car's nose to dip, which makes the suspension work harder. And you can overheat the brake rotors, which leads to warping.

Ray: Plus, you surprise the cars behind you, which is never a good idea.

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.