Dear Doctor:

My 2011 Chevrolet Traverse with an inaccurate gas gauge. It never reaches the full line. It’s my understanding that other GMC vehicles have been recalled due to similar issues, but I could not find any recall info on my Chevy. The Traverse is still under a factory-issued extended warranty. What work is involved in this repair?

— John

Dear John: To check the fuel gauge, fill the gas tank and bring the vehicle to the shop so the technician can connect a scan tool and look at the actual fuel level that is being sent from the gas tank. I have seen a lot of faulty fuel level senders. The technician will have to drop down the fuel tank to access the fuel sender unit if the fault lies in the sender.

Dear Doctor: I just purchased a 2017 Toyota Highlander. I have 500 miles on it — mostly local driving. The computer reads that I’m getting around 15.1 mpg. Toyota claims the SUV should get 20/27 mpg. I realize that actual mileage is below the EPA-rated mileage, however, getting 5 mpg less seems a bit unusual. The dealer suggested I drive it another 500 miles because the computer needs some kind of period of adjustment. This sounds like nonsense. Do you agree?

— Mike

Dear Mike: The new engine needs at least 1,500 miles to break-in all the internal moving parts. The computer also learns your driving habits and will adapt to the way the vehicle is driven. If you want to monitor gas mileage, fill the tank and zero-out the odometer, drive the vehicle 200 miles and then fill the tank the same way at the same pump and see how many gallons it takes to go another 200 miles. If the engine was running rich, it would set the check engine light.

Dear Doctor: Two years ago I purchased a 1977 Datsun 280Z. The owner gave me his records on maintenance for oil changes and tune-ups and general maintenance. But I noticed there were no records for changing the transmission fluid or the rear differential fluid. The 1977 owners manual calls for API GL-4 gear oil for the transmission and API GL-5 gear oil for the differential. I plan to use Valvoline HP 80W-90 gear oil for both applications (which states it’s rated for both GL-4 and GL-5), along with Valvoline 20W-50 racing motor oil with high zinc. I was asked if I wanted to use a synthetic, but I’m not sure if a 40-year-old car will be OK with synthetic fluids.

— Roger

Dear Roger: I have switched over several manual transmission vehicles to full synthetic, as well as rear differential fluids without ever having a problem. Engine oil can also be changed to synthetic, as long as you use a brand that meets older engine specs — and the zinc additive is a must of older engines. I do not think you need the HP 20-50 racing oil. A good synthetic would be a better option.

Dear Doctor: I had my 2003 Buick LeSabre serviced with an oil change, tune-up, transmission fluid change and replacement of two motor mounts. Now, the engine vibrates at idle. The mechanic replaced the mounts with another brand (neither replacements was GM) but the problem remains. Do you have any suggestions?

— Edward

Dear Edward: To feel a vibration at idle that was not present before the engine mount replacement, means there is metal contact from an engine mount. With the engine at idle, have the technician use a large pry bar and try moving the engine in any direction and see if you feel the vibration diminish. There could be other reasons for the vibration, such as the wrong length fan belt or exhaust hitting the frame.

Dear Doctor: My mechanic changed the spark plugs and wires and did an oil change on my 1999 Nissan Pathfinder. Ever since then my service engine light has been going on and off. Why?

— Dave

Dear Dave: Have an ASE-certified technician scan the computer for fault codes. It’s possible your mechanic may have left off a small vacuum hose or did not connect a sensor wire.