Q: My spouse and I take our Subarus to the dealership for service. Every time I take my car in for an oil change, they do a multipoint inspection that labels all parts/systems as green, yellow or red and encourages you to fix or replace when in the yellow range.

I question the reliability of the inspection. Once they marked my battery green, and a month later, when my car wouldn't start, they said the battery was severely corroded. Another time, I replaced one tire, and two weeks later they said all four tires were in the yellow range. I'm considering changing to an independent garage. Is the dealership's inspection worth it?

A: Car dealers often create their own mileage/time service charts. Sometimes, they do not jibe with the service schedules in the owners' manuals. You are within your rights to go to any service shop you like. This even applies while your vehicle is under warranty; just be sure to keep copies of your bills' itemized services.

Play it smart

Q: I bought a 2017 Ford Expedition and waited until the "Intelligent Oil-Life Monitor" told me I needed an oil change. My local dealer told me I should have it serviced every 5,000 miles or 6 months. I told them the manual says to change it when the IOLM system tells you to, but not to exceed 10,000 miles or one year.

I e-mailed another dealer asking for their recommendation. The customer service rep told me they would defer to my dealership. Seems like the manufacturer should have a position (and it would match the manual). Can I trust the IOLM system?

A: See the answer above. The manufacturer does indeed have a position. It is clearly stated in the owner's manual. Car companies have little influence on their franchise dealers after the vehicles are sold.

Common error

Q: I took my 2005 Ford Ranger to a Ford dealer hoping to solve an issue with it dying while driving. They determined it was the fuel pump. I went to another mechanic who said it was the inertia switch, which solved the problem. How did the dealer get it wrong?

A: The inertia switch, sometimes called the fuel cutoff switch, was installed as a safety device to shut off the gas in the event of a collision. You would be surprised how often it is overlooked as a cause of no fuel delivery.

Subtract additives?

Q: What is your opinion of additives? The ads say they reduce friction and engine damage.

A: I have not used aftermarket additives in my engines, and they have gone hundreds of thousands of miles with regular oil changes. If the compounds in the stuff are so useful, I question why they are not already in motor oil. Additives (e.g. STP, Marvel Mystery Oil, etc.) do no harm, and if they give you peace of mind, you can use them.

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.