Engine air filter

Regarding air pollution, it depends what you mean. Most of the gas pollutants (NOx, CO, Ozone) will pass right through the filter. Some of the more reactive ones might chemically interact with it, but not in a way which is going to change its function measurably. On the other hand, if there is a lot of soot, dust, or even pollen in the air that will clog up the filter in short order. The worst of all worlds is embers, as when driving near a big fire. Embers can and do light the paper air filters on fire. This happens pretty frequently to the cops who have to go up and down the streets ordering people to evacuate as a fire closes in.

Occasionally filters will clog up with leaves. This doesn't happen very often though. It needs some condition to put a lot of leaves up in the air while the car is driving through them. If it does occur that is one of the few instances where blowing out the filter and putting it back in might be warranted.

Anyway, instead of worrying about it, just put in a new air filter. They are pretty cheap. Compare the old one to the new one at the swap and you can see how dirty it is, which generally, but not always, indicates how clogged up it is.

 

There are a lot of things that can affect mpg’s on a Prius.
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Air filters are cheap. If it bothers you then just replace it. But it would have to be really dirty before it affected mpg's.

Lots of things can affect mileage. Restricted exhaust, tire pressures, wheel alignment, HV battery condition, etc.

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Once a year take it out and hold up to a light. If there is crud in the crevices replace it.

 

Poor mileage in an old G2 is usually because the hybrid battery is on its last legs. You have to really give it the gas to get anywhere because the hybrid battery is not providing any power. Start watching the battery meter on the mfd.

If the battery tanks to no blue bars or a purple bar its battery time. Its just the age. At 2007 its long overdue.

 

I’ve read a partially clogged air filter will improve mpg; it reduces air flow, the cars computers accordingly reduce fuel injected. You’ve essentially downsized the engine. Acceleration suffers a little.