Philadelphia Weekly

A MISSING AIR FILTER ISN'T THE END OF THE WORLD

Dear Tom and Ray:

I'm sure you guys have heard them all, but I just about fell over when this one happened to me. About seven months ago, my wife dutifully took our 1999 Subaru Forrester in for its 60,000-mile service. When I recently decided to replace the air filter myself, I opened things up to find ... no air filter at all! Looks like they forgot to put it back seven months ago. My questions are: 1) what kind of damage to the engine might have been done by driving for seven months with no air filter, and 2) what can/should I do about it?

Andy

RAY: Well, unfortunately, Andy, we haven't heard anything about a ring of air-filter thieves in your area, so you're probably right that the filter's been missing for seven months.

TOM: The air filter's job is to keep small, abrasive particles out of the engine's cylinders. When the engine is running, air is continually sucked in. The air filter is supposed to catch everything but the air.

RAY: If your air filter's missing and you suck in something flammable, like a piece of a leaf, it'll simply burn up in the cylinders and come out the tailpipe, and no damage will be done. But if you suck in something that's not flammable, like a grain of sand or a hard piece of dirt, it could scratch up the walls of the cylinders. And that can lead to piston-ring damage and oil burning.

TOM: So what are the chances you've done damage? Hard to say. First of all, some of these early Forresters had two air filters. Why? We have no idea. Why did Subaru switch back to one? No idea either. But if your Forrester happens to be one of the cars that uses two air filters (ask your dealer), you might have lucked out. All you'd have to do then is change both of them and forget about it.

RAY: But let's assume your only filter was missing, Andy. If you've been driving on dirt roads a lot, I'd be concerned. But if you're like most of us and drive every day on normal paved roads, you're probably fine.

TOM: So then the question becomes: Can you let this go, or are you going to obsess about it forever? If you're going to drive in fear for the rest of this car's life, thinking that every noise you hear is related to the missing air filter, then you have to get it checked out, just for your own peace of mind.

RAY: Start by going back to the dealership and showing them that they forgot to install an air filter. Then, while they're momentarily embarrassed and vulnerable, tell them you'd like them to pay for an independent shop to inspect the cylinder walls for damage. They might go for it.

TOM: The best tool for the job is a scope. A number of shops have a small, flexible fiber-optic scope that they can stick in the spark-plug hole to see the insides of the cylinders. It's the same thing your doctor wants to stick in you once you've reached the age of 50.

RAY: And since any shop that has a scope will be familiar with what cylinders look like at 60,000 miles, it should be able to tell you if there's excessive wear and scratching on your cylinder walls--or if your car just needs more fiber in its diet.

TOM: If everything looks normal, forget all about it. But if there is significant damage, at least you'll have independent verification of it, and you can ask the dealer to take responsibility.

RAY: Honestly, my guess is that it'll be fine, Andy. So feel free to replace the filter and get on with your life. But if you're going to worry about it and lose sleep, then get it checked out. No Subaru is worth losing sleep.