How does a dirty fuel filter decrease fuel economy?

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Sep 22, 2004
New Brunswick
To me, I would have thought that a dirty fuel filter would somehow increase fuel economy from restriction of fuel flow so less is burned or whatever. I changed the fuel filter in my 96 Sunfire, and doing the ol' blow-through-the-filter test, the old fuel filter was quite restrictive. The new filter, a FRAM unit BTW, was quite a bit less restrictive than the old one. So that's supposed to increase fuel economy somehow? We'll see how it goes I guess.
I don't know for sure that a clean fuel filter will actually increase gas mileage but a clean air filter surely will. Your really best off changing the fuel filter so you don't have to pay the cost for a new fuel pump.
I don't know about MPG, but you should notice an increase in power. Have had several clogged/dirty filters that I replaced and noticed and increase in power right away.
A clogged fuel filter will result in hesitation and eventually engine fuel starvation all together. It will not affect fuel economy, only engine performance.
A clogged fuel filter will eventually get so clogged that the engine will stop running. You don't want this happening when you're driving in a rural area a long way from the nearest town after all the sevice stations have closed. So if its starting to get clogged, change it. I have for many years carried a spare fuel filter in each of my vehicles and have, upon buying each vehicle, learned where the fuel filter is located and how to change it. And I taught my wife where it is and how to change it.
You also don't want this happening in the middle of rush-hour traffic....

The very next day I bought a new fuel filter. I found the old one by looking for something that looks like the new one. I otherwise had no idea where to find it.

It in fact died again on the way to the parts store.
As long as the filter is allowing a sufficient volume of fuel through to feed the injectors, your mileage shouldn't change. If it's clogged to the point that fuel pressure at the injectors drops below spec, you'll see poor performance and mileage will probably suffer along with it. Rough running and check engine lights could also be symptoms. In most cases, fuel filter changes are merely a preemptive measure to stave off potential problems. Don't expect any gratification from changing it unless it was the source of a problem you were having.
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