Archive for Thursday, August 26, 1999


August 26, 1999


Dear Tom and Ray:

When is it time to stop following the manufacturer's maintenance schedule? I have a 1993 Volvo 940 Turbo Wagon with 102,000 miles on it. For the most part, I have brought it to the dealer for all of the scheduled maintenance. That means spending something like $500 or $1,000 a year, even if the car was running perfectly when I brought it in (to be fair, those bills included brake jobs and exorbitant repairs to such essential equipment as the seat heaters). But at this point in the car's life, should I continue to go for the hefty routine maintenance visits or just wait until things break? -- Steve

RAY: Keep doing the maintenance, Steve. This is a mistake a lot of people make. Once they get to 75,000 or 100,000 miles, they assume the car is on its way downhill anyway, so they throw away the book and stop doing the routine servicing. And it's a self-fulfilling prophecy.

TOM: Right. You stop taking care of it, things start to wear out, and you take the car in one day and they tell you you need $8,000 worth of work. And you say, "That's ridiculous. On a car with 120,000 miles, I'll just junk it."

RAY: But if you kept doing the maintenance, you'd invest your $500 or $1,000 each year, and you'd probably never face the $8,000 dilemma.

TOM: Right. They'd get it $1,000 at a time over, say, eight years. And our Volvo-owning customers tell us it doesn't hurt nearly as much that way.

RAY: Actually, if you keep up on the maintenance, you'll likely spend less in the end and have a car that runs better and lasts longer. So the answer to your question -- "When is it time to stop following the manufacturer's maintenance schedule?" -- is "never."

Dear Tom and Ray:

Can you think of any reason why a catalytic converter would catch fire while driving? -- Sharon

TOM: No.

RAY: I've certainly never seen it happen. And I've had cars come into the shop with converters that were absolutely glowing red.

TOM: But it's possible for things AROUND the converter to catch fire. If your engine was running rich or your timing was very retarded, a lot of the gasoline could have been combusting inside the converter instead of the cylinders (those are the most common explanations for red-hot converters).

RAY: So, if your converter was running hot and you ran over a garbage bag and it got stuck underneath your car, the garbage bag could have caught fire. The same could be true of a bunch of dried leaves or a flowering tulip tree that you ran over 20 miles earlier and wedged between the converter and floorboards.

TOM: But I've never seen a converter itself burst into flames. So if you're looking for an explanation for a fire that started under the car, look for something the converter could have ignited rather than the converter itself.

RAY: And if the car still exists (you don't indicate in your letter), make sure the fuel-air mixture and timing are correct and that the converter is operating properly before you drive over your next tulip tree, Sharon.

Dear Tom and Ray:

Because I don't think about cars at all (unless there's one coming at me at a rapid speed), this question may be very dumb. My sister says that different brands of gas, even though they're the same octane, will produce different amounts of mileage. She says she can buy one brand of gas and get from Pittsburgh to Carlisle, Pa., on a quarter of a tank, while another brand will burn half a tank going the same distance over the same roads. She attributes this to the octane rating being an average and says that some companies cheat with their numbers. Is she full of gas? -- Sandy

TOM: Full of gas? No. Full of something else? Sounds like it to me!

RAY: While there are very slight variations in the octanes of gasolines you buy, it's nothing you would ever be able to measure with the equipment you're using (for example, a 1992-era Ford Escort and a dashboard gas gauge).

TOM: Right. There's no way that different brands of gas of the same octane could produce mileage differences this great. My guess is that when she "fills up" the tank, sometimes she fills it more "up" than other times.

RAY: The dashboard gas gauge is a very rough estimator. Even though the gauge may read "full," there may be room for another couple of gallons of gas in the tank itself. And that would explain why she sometimes arrives at her destination with the gauge reading half-full.

TOM: Other times, when she really tops it up and puts in as much gas as it will take, it's only down a quarter when she arrives.

RAY: Dashboard gas gauges are good as relative measures. They tell you when the tank is pretty full, and when it's pretty empty. To use them for anything more precise than that is like using your kitchen scale to weigh molecules of radioactive plutonium (which our lawyers have asked us to remind you not to try at home).

TOM: If she wants some slightly more accurate numbers, Sandy, tell her to fill up the tank (and stop when it automatically shuts off the first time), drive to Carlisle and record the number of miles driven. Then fill it up again the same way, do the math and figure out how many miles per gallon she got. That method is not approved by the Federal Bureau of Weights and Measures either, but it'll be more accurate than what she's doing.

Got a question about cars? Write to Click and Clack in care of the Journal-World, 609 N.H. Lawrence 66044, or e-mail them by visiting the Car Talk section of on the World Wide Web.

  • Car Talk with Click and Clack airs at 9 a.m. Saturdays on KANU-FM 91.5.

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