Q.  For the first 30,000 miles I used regular oil in my 2002 Toyota Corolla. For the next 40,000 miles I used synthetic oil. For the past 40,000 miles I have switched back to regular oil. Now the car is using a quart every 500 to 600 miles. Could I have harmed the engine by switching oils?

A.  It is perfectly acceptable to switch back and forth between conventional and synthetic oil. I wouldn’t expect a Toyota Corolla to burn oil at 110,000 miles, but the car is nearly 10 years old. If you’re concerned about the oil consumption you could have a compression test and cylinder “leak-down” test performed. This test will help determine how the oil is being burned, although at this point it just might be cheaper to add one quart once or twice per month as needed.

Q.  My 2007 Hyundai Azera Limited has been very reliable, but earlier this year I noticed a couple of chips on the hood just below the wipers. I assumed that rocks had caused the chips, and took it to a garage where the area was repainted. A month later the chips resurfaced in the same spots. The Hyundai dealer said it was probably from rocks. They had no information indicating that this was a common problem with this model. These chips are especially annoying since I keep seeing them as I drive. Have you encountered this issue?

A.  I haven’t seen this problem before, and after looking on several automotive forums it doesn’t appear to be an issue with this model. I’d return to the shop that did the repair; many will warranty their work for one year. You might also include a paint film. This is a nearly invisible clear adhesive that’s installed on painted surfaces that tend to suffer from “road rash”.

Q.  Late last year, when my 2004 Ford F150 four-wheel-drive truck hit about 70,000 miles, I started hearing a whining noise from the drive train. I thought it was a universal joint but they checked out fine, as did the wheel bearings. Any thoughts on what it might be?

A.  First, you need to do is determine where the noise is coming from. This model has had two distinct problems. One is internal to the transmission; but if you’re lucky, it’s just a clogged transmission filter. The other common problem is a noisy rear differential. Once you determine where the noise is coming from, you can determine what needs to be repaired. Unfortunately, just about any of these repairs will be expensive.

Q.  My 1995 Jeep Grand Cherokee Orvis edition has 108,000 miles, and lately the display shows “service four-wheel-drive.”  This message flashes and then goes off. How can I solve this?

A.  It is my understanding that “Service 4wd” in the cluster means there’s a final-drive control-module (FDCM) fault. This can be from a lack of communications caused by a software glitch. In many cases it can be fixed by a computer flash update. Your shop should refer to technical service bulletin number 21-014-06 REV A.