I have a 2014 Ford Focus with not quite 18,000 miles. It has the original air filter. The dealer says the air filter is fine and won’t change it out, even when I told them to.

Should I do it on my own? Does the filter break down over time? Thanks. -- Lee

RAY: We’re going to have to give this dealer a 15-yard penalty for refusing to sell you unnecessary parts, Lee. He’s clearly trying to make the rest of us look bad.

Honestly, I can’t remember seeing an air filter break down over time, Lee.

The filter is made of pleated paper, surrounded by a rubber gasket. But it’s fairly coarse paper. Put it this way -- it’s not something you’d want to wipe your behind with, even in an emergency. It’s not flimsy.

Air filters tend to get dirty way before they disintegrate -- barring intervention from a family of mice or something like that.

It’s even possible that when you’ve previously been in for service, someone removed your air filter and blew it out with compressed air -- removing any dirt and dust that it captured for you.

So, is it possible for an air filter to still be good after eight years and 18,000 miles? Absolutely.

Changing or cleaning the air filter was much more important in the days of carburetors -- like pre-1980s. In those days, if your air filter was really dirty, it would reduce the air flow to the engine and mess up your fuel-air mixture. That’d make your car run poorly, harm your emissions equipment, and really reduce your mileage.

But with computer controlled, fuel-injected cars like yours, even if the air filter were dirty enough to limit your air flow, the computer would just adjust the fuel flow to match it. You might notice a little less power, but your mileage and emissions equipment would be unaffected.

So, if your dealer checked your air filter and says it’s clean, there’s no good reason to change it.

On the other hand, we don’t want you to lose any sleep over this, Lee. So, if it really bothers you, stop by the parts department and buy a filter for less than $20 and install it yourself. It’ll take five minutes.

Technology on newer cars is rightfully enviable

My wife has a 2012 Mercedes E350 Blutec. It has 33,000 miles on it. It looks new and gets 37 miles per gallon on the highway.

She envies the technology on my 2018 GLE 350. If I trade in her car, what would you recommend? She doesn’t like my SUV. -- Don

RAY: Get her a nice 2022 S-Class, Don. What kind of husband are you? Letting your wife drive around in a mere E-Class with almost 34,000 miles on it? That’s barbaric.

Actually, Don, if she likes her E350, she’ll probably like an E-Class that’s 10 years newer. And 10 more years up to date.

She’s right to envy the technology on newer cars. Newer cars, like the current E-Class, have automatic emergency braking that applies the brakes if a car stops in front of you and you don’t react in time.

They have adaptive cruise control that maintains a set distance between your car and the car in front of you on the highway.

They have blind-spot monitors that warn you when a car is coming up on your flank. And they have rear cross traffic warning to let you know when a car is coming down the street toward you when you’re backing up.

Today’s cars can nudge the wheel to keep you from drifting out of your lane, and some even monitor your eyes and warn you if you’re getting drowsy on a long trip.

I know she probably likes the fuel economy she gets with the Blutec diesel variant. A new gasoline powered E350 won’t do as well. But it’ll be quieter, and your neighbors won’t hold their noses when she pulls into the driveway.

Or better yet, she could be an early adopter and go for Mercedes’ brand-new, all-electric S-Class, the EQS. We just drove it, and it’s fantastic. The only problem is that then you’re going to envy her technology, Don.

Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.