Q: My mother-in-law recently gave a 1991 Lexus LS 400 to my wife and me. She bought the car brand new in 1991, and now it has about 75,000 miles. We had to install a starter, brakes and rubber suspension boots to safely drive the car from Los Angeles to Seattle. I've heard these cars are bulletproof up to 200,000 to 250,000 miles. Assuming I perform regular maintenance, do you think that I can expect this kind of mileage from the car?—Rich Goodman, Everett, Wash.
A: You should be able to reach 200,000 miles in that car if you really take care of it. The LS 400 is a very reliable luxury sedan, but you should consider changing the timing belt because of its age.
Q: We have a 2010 Infiniti EX35 with 30,000 miles. The dealer wants to replace both the antifreeze and transmission fluid as part of the 30,000-mile service. I thought those were more like 100,000-mile items. If they really need replacement, I am disappointed in the life but I guess I can do it. However, I wonder if this is just overly aggressive maintenance. The cost is nearly $700 dollars. Is this
A: Double-check your owner's manual for prescribed fluid-change intervals, though I think your dealer is charging an inflated price for services that are simple and often largely unnecessary.
Q: In all the discussion about automobile fuel economy, I don't recall ever seeing any data about what is the maximum range, or best speed for fuel economy, for a car. This information is standard for aircraft, but doesn't seem to be for cars. No doubt the speed is different for every car, but is there a rule of thumb that could be used if, say, I am 50 miles from the nearest station and the fuel warning light has been on for 30 minutes?—Tom Rattle, West Linn, Ore.
A: Optimum cruising speed for maximizing fuel economy varies by vehicle, though 40 miles per hour to 45 mph is a good place to start. And be sure to accelerate smoothly and drive steadily at the optimum speed.
Q: I bought a 2005 PT Cruiser GT Turbo Convertible in Florida with 3,500 miles on it. I have since put 27,000 almost trouble-free miles on it. I love driving it but I read that these cars have many problems. Should I quit while I'm ahead?—Jack Collins, Venice, Fla.
A: Some PT Cruiser convertibles are gems while others are dogs. If your car is running well and you enjoy driving it, there is no need to give up on it, but you should pay special attention to its maintenance schedule.—Email email@example.com
A version of this article appeared January 15, 2013, on page D4 in the U.S. edition of The Wall Street Journal, with the headline: Columnist Jonathan Welsh answers readers' questions about automobiles.