Solving the ‘Mystery’ of using a fuel and oil additive

Q. I perform routine maintenance on my family’s cars and just want to know your thoughts on Marvel Mystery Oil as both a fuel additive and oil additive. Is this product really beneficial for both? Also, what are your thoughts on oil flush additives before an oil change?

A. I think nearly every mechanic has used Marvel Mystery Oil for everything from engine lubrication to oiling shop air tools. I have used it on an older engine to quiet noisy valve lifters and even added some to an engine that had not run in years, and had good luck. The issue is more on a modern engine. Marvel Mystery Oil changes the viscosity of the oil and can also affect the additive packages in modern oil. The problem is it could work great, or it could cause a problem, and there is no way to know unless you have the oil analyzed. As a regular additive I would be cautious about using it. As for adding it to fuel, I do not see a problem of adding a few ounces periodically when filling the gas tank to help clean combustion deposits. Regarding oil flushing, if the oil is changed on a regular basis, I see no need for adding a flushing chemical. In fact, many car manufacturers recommend against it. 

Q. Do you know the name of the yellow plastic piece that holds the wires against the radiator and then goes to the fan? I am replacing some parts in a 22-year-old car, and I am trying to buy new ones, but the dealer was not much help. They said the car is too old. 

A. I assume you mean a wire loom retainer or wire retainer. There are different types, screw-on or bolt-on clips, or push-in styles. Go to a local auto parts store with one of the old ones, even if you break it, and look for a Dorman display. Dorman tends to have all kinds of hardware solutions, and I think you will find something that works. 

Q. I belong to a car club and we have monthly cruise nights. I was at one over the summer and noticed you sponsored the dash plaques. How do I go about getting you to sponsor plaques for our event? 

A. Go to your nearest AAA office and ask to talk with the manager. Some offices have a budget for community events, especially if those events help support local charities. 

Q. I have a 2007 Toyota RAV4 with about 235,000 miles. The driver’s side seat has two rips/tears and the seat back upholstery is showing some stress. The passenger side seems OK. Where would the best local-ish place to go for seat repair?

A. Like finding a good repair shop, doctor, or dentist, finding a good upholstery shop can be a challenge. Personal recommendations are always the best. Check with social media and even local body shops. Some upholstery shops may have no interest in trying to repair a worn seat, if it is even possible. A better and potentially cheaper option may be a set of DIY custom seat covers. I was recently looking at a set for a similar vehicle on an online site — CarID.com – and they had what looked like a nice neoprene set for less than two hundred dollars.

Q. What is the cost of a muffler for a 2008 Toyota Corolla?

A. It really depends on where the work is performed, the quality of the parts used, and what actually needs to be replaced. If it is just the muffler, the muffler and labor at the dealer would be around $500, at an independent shop using non-Toyota parts about $250. If the pipe that connects to the muffler needs replacement, then it becomes more expensive, since that pipe includes the catalytic converter, which can add $1,000 or more to the price. 

Q. I have a 2015 Subaru Forester with only 26,067 miles. The car failed inspection last year in October because the car’s computer system was not ready to be tested, as the car was not driven enough. I paid the dealer to drive it to pass inspection. I am elderly and use the car locally. I am afraid of the same problem again. Can I monitor the car’s computer system, so I know it has enough mileage to pass inspection? Is there a device to use? Can you recommend on average how many miles per month or year the car needs to be driven to avoid this problem?

A. On all newer cars there are readiness monitors. These monitors keep track of several systems in the car, such as the catalytic converter operation, fuel system, and oxygen sensors. Typically, once the monitors are set you should be fine. Perhaps last inspection you had the battery replaced or other maintenance erased the car’s computer memory and cleared the monitors. Without going through the inspection process, a technician with a scan tool can quickly tell if the car is ready to be inspected.

John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your Car Doctor question to [email protected]. Listen to the Car Doctor podcast at johnfpaul.podbean.com.