Q: I have a 2005 3.8-liter Chrysler Town & Country with about 152,000 miles on it. It has a constant engine noise like a diesel pickup truck when parked and idling. The Chrysler dealer was not sure what was making it and suggested they start by replacing the generator or water pump and see if that solved the problem. I decided against this trial-and-error method and took it home and kept driving it. It has been months now and neither the generator nor the water pump has failed. I seem to remember an article you wrote that suggested checking the timing chain/belt and tensioning sprocket. Do you think this could be the issue with my Town & Country?

A: I agree that a "shotgun" approach to identifying the source of the dieseling noise doesn't make much sense — except to the shop charging for the parts and labor! Since the vehicle makes this noise while idling in park, a technician should try to pinpoint the location where the noise is coming from with a mechanic's stethoscope. By touching the tip of the tool's pickup to the belt-driven components like the alternator, water pump and power steering pump, then the timing cover, valve cover, cylinder heads, exhaust manifold, block, etc., there's a very good chance of pinpointing the noise.

Q: I drive a 2006 BMW Z4 with only 25,000 miles on the odometer. I intend to keep the car indefinitely and as a result, I try to keep it in excellent condition. I also drive a 2014 BMW X1 with the M package and four-cylinder turbocharged engine. Are there advantages to using ethanol-free gasoline in these cars? I'm aware that owners of older classic autos use ethanol-free fuel and wonder if it would benefit me to do likewise.

A: Both your vehicles — and virtually all vehicles built in the past two-plus decades — are engineered to deliver good performance, mileage and longevity operating on ethanol-blended fuels. Strictly speaking, there should be no advantage to operating on non-ethanol fuels. Perhaps more important, in many states the ethanol-free fuel is often sold for specialized equipment such as collector cars, boats, off-road vehicles and small engines.

But if you were able to ask your vehicle which fuel it prefers, I suspect it would choose 100 percent gasoline. Theoretically speaking, the advantages of operating a late-model vehicle on non-ethanol fuel would be slightly better fuel economy, less chance of fuel system deterioration and phase separation of water and fuel, particularly in vehicles operated infrequently.

These small benefits are offset by significantly higher costs, potential legal issues, far fewer locations to purchase and the compatibility of ethanol-blended fuels with today's motor vehicles.

I do accept the effort and cost to fill my "special" vehicles and equipment with non-ethanol fuel, but I don't worry about this with our daily drivers, including my C6 Corvette.

Q: I have a 2004 Volvo XC90 with 275,000 miles that is still serving as a daily driver! It runs great, but at this mileage I can't find much meaningful maintenance guidance online. In regard to oil viscosity, I decided to try 20W-50 last summer, with pretty good results — I got almost 3,000 miles before a quart was needed. The thinner oil won't quite go that long anymore. I just completed a 14-hour freeway trip to Tucson from Dallas, and with 10W30 the car consumed a quart or more in the 1,000 miles. Any reason not to go with 20W-50 or synthetic 15W-50 on a car with this many miles? And maybe retire it from cross-country drives?

A: I'd stick with the 20W-50 conventional oil because the synthetic costs considerably more and may generate higher oil consumption due to its uniform rather than random molecular size. And why retire the car from road work? The vehicle has a great durability record and unless oil consumption increases significantly, it should continue to deliver excellent service.