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Changing air filter WON'T save me gas?

On p.30 of the July issue of Money, under

“Five Gas-saving Myths” it says “a clean air filter isn’t going to save you gas. Modern engines have sensors that adjust the

fuel-air mixture as an increasingly clogged

filter chokes off the oxygen supply.” That’s cool, BUT: Is the 4-cyl. 1.6L DOHC engine in my 1997 Geo Prizm (Corolla twin) a “modern engine” with such sensors?

Shouldn’t I at least have my mechanic take an air hose & blow out the filter, from back to front?

If the filter is clogged, replace it, don’t “blow it out.” You may open up some holes to let dirt into the engine. Also, just because it won’t save mileage, doesn’t mean it shouldn’t be changed when dirty. If your Prizm has a MAF (Mass Air Flow) sensor, then a clogged filter will reduce max power available, but not mileage. A really dirty old filter may start leaking dirt into the engine.

I didn’t necessarily agree with that article and you have to take into consideration who wrote it. Just because Money says something doesn’t make it so. Yes it is a modern engine but it can only adjust the mixture so far. What does an air filter cost, $10? Seems like foolish advice to me.

Be suspicious of the advice in Money magazine. Their main business is publishing. Even if you wouldn’t save gasoline with a new air filter, it doesn’t mean that you want a clogged one. There’s power to consider, and the engine was designed to run with an unclogged filter. Optimal performance is what we want. Since the material for the article could be over twenty years old; your engine qualifies as modern.

A clean filter and a filter that needs changing…there probably is very little difference in gas mileage. However a real dirty filter can drastically effect gas mileage. And in the long run keeping your air filter clean will effect gas mileage by NOT letting dirt accumulating in the throttle body.

I’ve read these exact same bogus stories. They’ve often the same old thing being rehashed by numerous “car experts” who have no mechanical experience.
You see this all of the time, even on non-auto related subjects. One person manages to get a story on the national news and then the local news outlets, just like sheep, repeat it with their own reporter/reporterette.

The one thing that is never taken into consideration is manifold vacuum and this has an affect on what the engine, and various sensors such as the MAP sensor, are doing. An engine struggling to breathe, even a little, will have altered vacuum to some extent and this will be read as a load being applied to the engine.

Other myths are ones that were repeated on the local news here a few weeks ago in which the young reporterette just out of journalism school no doubt breathlessly recited a number of “gas saving tips” such as overinflating your tires to 40 PSI and the really goofy one - turn the interior cabin fan down to it’s lowest speed. That will allegedly cause “the A/C to work easier and improve mileage”.

Even some car makers recommend things like never changing the auto transmission fluid filter, fuel filter, or extended intervals for air filters and those recommendations are not good for the car. Good for the car maker; just not for the car owner. Depending on the environment, sometimes a new air filter may need changing again a month later.
Around here, I even have to clean out my home central air condenser unit twice a year.

Forget blowing the filter out. It may knock out the larger particles but the microscopic stuff you don’t see is what is really clogging the filter and most of that will remain in place. A filter may appear to be clean visually and yet still remain half-clogged. JMHO anyway.

Agree; change the air filter; most pick up enough dirt over time to impede air flow.

Money magazine? Ha!

The only time that I made bad investment decisions was when I acted on advice in Money magazine. Since their investment advice is…let’s just say…not very good, and since they are not an automotive magazine, I certainly wouldn’t take their advice on anything regarding a car. If they can’t advise well in their supposed area of expertise, how could you depend on their advice in an area that is clearly not in their area of expertise.

That being said, even if they were correct about a clogged air filter not affecting your gas mileage, do you think that they would pay for replacing your MAF sensor when it is ruined by following their flawed advice? I don’t think so.

When you are cruising down the highway at the speed limit, there is a pretty high vacuum in the intake manifold. Most of that vacuum, probably over 99.99% of that vacuum is due to a nearly closed throttle, not due to air filter restriction. A closed loop electronic fuel injection system can compensate for a slightly more restrictive air filter just as it compensates for 100 degree temperatures and mile high Colorado altitudes.

Now, back when dinosaurs roamed the earth and all cars had carburettors, a restricted air cleaner would act like a choke and cause the air/fuel mixture to go richer and that resulted in bad gas mileage.

Still it’s good to routinely replace the air filter just to protect the engine from dirt.