Q: A blinking check engine light came on setting a number four cylinder misfire code. I suspected a bad ignition coil, which I replaced. I cleared codes and the car runs great. I was able to find an auto parts store open late and fortunately the coil was in front of the engine not in back. A back coil will probably fail in dead of winter and 20-below temperature. I would like to replace the back coils and I can get a better brand coil at less cost. Is it OK to mix coils from different manufacturers?

— J.D., Chicago

A: Yes. Every manufacturer must build their parts to the original equipment specifications. That said, I prefer to stick with parts from the same company.

Q: My normal gasoline station (a Sam's Club) has traffic flow in one direction only at its pump islands. I've noticed that there is always a line with multiple cars for vehicles with gas caps on the left side, but rarely any line for vehicles with gas caps on the right side. Just a rough guess but I would say that about 80% of the vehicles on the road have gas caps on the left side. Right vs. left side: How is this choice made during the design process? Is there a statistic for the percentage of vehicles on the road with gas caps on the left vs., right?

— M.M., Springfield, Ill.

A: It seems that that there are statistics for everything, although baseball seems to have the most. If there are gas cap stats, I could not find any. My hunch is that design engineers look for the most convenient location with the shortest distance from the tank to the inlet, which is usually denoted on the instrument panel with an arrow beside the gasoline icon.

Q: I purchased a new 2021 Tucson this spring. My first new car in 17 years! I love it but have a question. We went to two dealerships and both salespeople said the oil change should be every 3,750 miles. I have taken my car in twice now, at 3,750 and 7,500. The service department is telling me I only need to come in every 8,000 miles. I have followed the 3,000 miles/3-month oil change guideline and tire rotation every six months for over 40 years. I don't want to void my new car warranty. Who do I believe?

— S.K., Minneapolis

A: Have faith in your owner’s manual, it is the car’s bible. Reading the maintenance section, you will find the service interval blessed by the carmaker. Thou shalt change the oil and filter once a year or every 7,500 miles. It seems like a sin to waste money on unnecessarily frequent oil changes.

Q: You recently wrote that using the cruise control provides better gas mileage. We have a 2018 RAV 4 and have driven from our previous residence in Virginia to Illinois several times. On one such trip I used the cruise control whenever possible, and on another identical trip I used the pedal only, which yielded an extra 2 mpg over cruise. I suspect the cause is the additional braking for slower vehicles and unnecessary shifting on inclines.

— J.C., Mokena, Ill.

A: Not everyone can finesse the throttle like you. When you lift your foot to brake, you close the throttle. Coasting to a stop helps, so does gently accelerating from a stop instead of returning to 55 mph as quickly as possible.

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(Bob Weber is a writer and mechanic who became an ASE-certified Master Automobile Technician in 1976. He maintains this status by seeking certification every five years. Weber's work appears in professional trade magazines and other consumer publications. His writing also appears in automotive trade publications, Consumer Guide and Consumers Digest.)