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Q: My 2007 Chevy Cobalt LT, with approximately 90,000 miles, has developed what I describe as the sound of a small plane propeller. I do not hear it when it idles, but as soon as the RPMs rise above 2,000, I hear it.
A: Although there is a panoply of possible propeller noise sources, I would check for a cooling fan problem or exhaust system leak.

Saving gas

Q: You recently had a question about fuel economy savings for auto start/stop technology. My Subaru Outback switches to a display that counts each second I am using that feature and shows an estimated fuel savings based on the total time I have done so. Per that display, my fuel savings are close to 3%. So, I think the feature is well worth it.
A: Thanks for doing the math.

A pricey fix

Q: My 2018 Dodge Journey has a problem with condensation build-up on the interior face of the lens of my headlamps. Can you help prevent this problem?
A: This is a common issue. Although there are numerous suggestions for drying out the headlight assembly, none seem to last very long. Replacing the assemblies is the ultimate solution, but it is an expensive job. The front bumper cover and grille must come off to access the assemblies. And then you have to add the cost of replacement parts. You might want to decide if you can live with the condensation.

Save your money

Q: I own a 2010 Audi A6 Quattro 3.0T. It has 75,000 miles. Audi does not have a fluid change interval for differentials, transaxle, transmission or coolant. Because my car has low miles and might be on the road for several more years, should these fluids be changed?
A: No.

Save more money

Q: I own a 2017 Ford F-150 with about 34,000 miles. When I was at the dealer for service, they recommended that they flush the transmission fluid at a cost of $318. I declined. The manual is confusing with respect to this service. Did I do the right thing?
A: At such low mileage, I wouldn't consider changing the transmission fluid.

Oil guide

Q: I seem to remember you've said cars typically consume one quart of oil for every 1,000 miles of driving. I've had the same Toyota Sienna minivan for 17 years and never had to put a drop of oil in it between oil changes. Am I confused about what I've read in your column?
A: You aren't confused. Maybe a bit forgetful. I did say that the automakers claim that as much as one quart in 1,000 miles is acceptable. Owners should check their oil regularly to be sure they aren't heavy users.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to