Q: I bought new a 2018 Mazda6, 4-cylinder turbo. The specs call for semi-synthetic oil. Everyone I know with auto expertise — including a former engineer friend from GM — thinks I should use full synthetic. The tech personnel at my dealership, including the manager, tell me to follow the recommended specifications. Any opinions?

A: Stick with what the manufacturer says. Although full synthetic oil is marvelous, it can cost nearly twice as much.

Switching oil not an issue

Q: I have a snowblower that uses two-cycle oil. Is it OK to switch between synthetic and regular two-cycle oil, and which is better to use? And how long does the oil last? Can I buy it in bulk, which would be enough to last me several years?

A: You will have no problems switching between traditional oil and synthetic in either your car or your snowblower. And you shouldn't have to worry about an expiration date. Go ahead and stock up when it is on sale.

Check the details

Q: I've seen on TV that you get 25 more miles to the tankful when you fill up with Amoco premium. We have Nissan Altimas. Nissan recommends regular gas. Will using Amoco premium cause any damage to the engine or void the warranty?

A: First, read the small print. A footnote on BP's website says that the claim is "based on median difference between 93 octane Amoco Ultimate and 87 octane minimum detergent E10 fuels in late model, full-size, half-ton pickup trucks." That's not what you have. As for your question, using premium gas instead of regular will have no impact on the warranty, but it will have an impact on your budget. There is roughly a 25% price difference, so using it in a car that runs fine on regular isn't worth it unless it also produces a corresponding increase in gas mileage.

Oil change advice

Q: I have a 2004 Toyota Camry with just under 60,000 miles. How often should I be changing the oil because I drive so few miles?

A: You can't go wrong changing your oil at 7,500 miles or once a year.

Cold causes squeaks

Q: Now that the weather has turned cold, the moonroofs in our cars squeak when we drive over bumps. What will stop the noise?

A: Silicone grease will reduce the noise and protect the gaskets.

The pandemic and plugs

Q: My 2011 Honda Fit was losing power because a cylinder was misfiring. I changed the spark plug and ignition coil, and the car is running fine. But it got me wondering: Now that we are driving less because of the pandemic, are the spark plugs more subject to fouling?

A: Perhaps, but not enough to create a drivability problem.

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 motormouth.tribune@gmail.com.