Q: When I first poked my head under a hood nearly 50 years ago, I was told that the cleanliness of the air filter was one of the factors that affects fuel mileage. I still hear it today, even though modern engines are controlled by computers. Because the computer and its associated sensors constantly maintain the optimum fuel/air mixture, it seems that a dirty air filter (within reason) would have little to no impact on fuel economy. Is the dirty air filter rule still relevant?
A: No. If the filter gets really plugged up, it could affect the amount of power you get. But it won't affect anything else.
Air coming into the engine passes through a filter. That weeds out pigeons, leaves and other dirt and debris. The air that gets through the filter then goes past a sensor called a mass airflow sensor that measures the density of the air that's coming in.
Then, based on that information, the computer decides, many times a second, how much fuel to inject to make the ideal fuel/air mixture in the cylinders. If the amount of air gets reduced over time because of a dirty air filter, the computer will adjust and send in less fuel to match it. So your mileage and, just as important, your emissions, will stay the same.
Crankcase ventilation systems work much better than they used to. In the old days, meaning 25 years ago, they'd send oily fumes through the filter and make it filthy in no time. But we rarely see dirty air filters in the shop these days, and when we do, it's usually because some rodent has been using it as a place to warm its nuts.
Beyond reliability
Q: I just traded in my 2004 Jeep Liberty for a 2020 Jeep Renegade Latitude with 4,000 miles. It was a demo. The sticker price was $29,000. I paid $21,000. It has all the bells and whistles: cold weather package, safety package, etc. I even got the color I wanted: Bikini Pearl Coat.
My son is a mechanic. He was, let's say, unhappy with my choice. He said, "Mom, it's a Dodge Neon engine in a Jeep body." I love my Renegade. I joined the JROG (Jeep Renegade Owners Group), and it seems most people love their Renegades. Did I make a bad choice? I got the extended bumper-to-bumper warranty because of the amount of electronics. Please give me some ammunition to use against my son.
A: Your best ammunition is "Your mom is happy, son." Granted, I'm in the same camp as your son in that the Renegade would not be my first choice, in terms of reliability or advanced engineering. On the other hand, my mom never wanted a car in Bikini Pearl Coat.
