A: I hear you.
Q: I drive a 2017 Acura MDX and the owner’s manual specifies that 91 octane fuel is “recommended.” The sales staff tells me that mid-grade (89 octane) or even regular grade (87 octane) is acceptable. I’ve used mid-grade for two years and the engine and performance are good. How does the engine determine the octane level and how does it internally adjust to fuel that is lower than the recommended grade? – K.K., Schaumburg, Ill.
A: With spirited driving, engine knock can occur, so the preferred fuel is one with a higher octane. Under less spirited driving, engine knock is less likely, so mid-grade or regular gas is fine. Continued engine knocking will cause damage, so a knock sensor screwed onto the engine reports the first signs of knock to the engine control module that then backs off the ignition timing until the knocking stops.
Q: We have a 2010 Toyota Highlander with 58,000 miles. On my last couple visits to the dealer for routine maintenance, they have recommended an engine de-sludge. We have kept up with oil changes and other maintenance at the recommended intervals. Is this something modern vehicles need or are they just trying to get me for another $170? – S. M., Skokie, Ill.
A: They are de-sludging your wallet. Select this service if your bulging billfold is bothering you.
Q: As a kid I remember that when I was in junior high, we always had air conditioning in our car, but my dad would never use it, saying it killed the gas mileage. He believed in 4/40 A/C. Now I never hesitate to turn on the A/C and I don’t seem to see a lot of gas mileage difference. Do the electronics in today’s cars really compensate the gas usage when the A/C is on? – R.F., Warrenville, Ill.
A: Ah yes, the 4/40—four windows down at 40 miles per hour. It was the poor man’s air conditioning for cars that did not have the system. Early automotive A/C was indeed a power hog. Compressors were large and clunky. Terribly inefficient. Automotive systems have come a long way becoming highly efficient. The electronics in a car are not really a factor.
Q: The maintenance manual for my 2016 MB 450 GLE Coupe says replace the spark plugs at 5 years/50,000 miles. But at my four-year service the dealer said 4 years/40,000 based on the MB 2016 Service Sheet. Customer Service says it’s a typo in the manual, which I question. – F.G., Libertyville, Ill.
A: You would be surprised how many dealerships print up their own service guides. All they need is some imagination, a computer and printer to make them look professional. Some service departments go as far as to post their service intervals boldly on the wall.
Q: I don’t understand how a fuel filter can be considered a lifetime part. I have a 4WD, 2003 Tacoma with 162,000 miles and when I asked the dealership about replacing it, I was told it does not need to be replaced. Nearly every other filter, like air and oil, are changed routinely so why not fuel? – C.M., Quakertown, Pa.
A: There is a filter on the fuel pump pickup pipe. Often called a sock, it protects the pump and everything beyond. Gasoline is much cleaner nowadays and gasoline dispensers have filters in them. I have seen cars go hundreds of thousands of miles without a fuel filter replacement.