Does fuel filter really affect gas mileage?

**Jerry99Sport** · Apr 20 2007, 05:56pm

I have been searching the boards for awhile trying to find ways to improve my gas mileage. In doing so I have found numerous suggestions to replace the fuel filter. Is there really any merit to that? I was told by a repair shop that a dirty fuel filter cannot possibly decrease gas mileage. If anything, it will restrict the flow of fuel, therefore improving gas mileage. This logic made a lot of sense to me. Then again, I am no mechanic and don't have much experience with the effects of replacing fuel filters. So can anyone who thinks replacing a fuel filter will improve gas mileage explain why?

**FallenPhoenix** · Apr 20 2007, 06:15pm

Anything that keeps the vehicle from working 100% how it should from the factory can have a detrimental effect on gas mileage.

Posted by Jerry99Sport

If anything, it will restrict the flow of fuel, therefore improving gas mileage.

Is this something the mechanic told you?

**Jerry99Sport** · Apr 20 2007, 06:23pm

Posted by FallenPhoenix

Is this something the mechanic told you?

To be honest, it was last year, and I don't remember if he actually said that or if that was just the "gist" of it. He made it sound like it would really be senseless to replace the fuel filter solely to improve gas mileage. But I definitely am not advocating not replacing the fuel filter on schedule, and I understand that any improvement in mileage from a dirty filter would probably be due to the car not starting

.

**dlibson** · Apr 20 2007, 07:50pm

Replacing a fuel filter can help milage in a couple ways. First, if it is clogged and not getting the fuel it needs, the computer will richen the mixture decreasing gas milage. Second, a clogged filter creates a lower level of power, which usually means you drive harder. There are other reasons, both those are the main two.

**PW01** · Apr 23 2007, 02:13am

What he said!

**Adam Baker** · Apr 23 2007, 08:39am

Replacing the fuel filter wont cause an increase over the base gas mileage. However, if its clogged, it can raise the mileage back to, or closer to, the original mileage.

**Jerry99Sport** · Apr 23 2007, 12:23pm

Posted by Adam Baker

However, if its clogged, it can raise the mileage back to, or closer to, the original mileage.

Right, that is what I am trying to do.

Thanks for the explanations. I guess the fuel filter affects more variables than I realized. But that repair guy (technically a service writer, not a mechanic) had me misled for months.

**Joe Turner** · Apr 23 2007, 01:58pm

Every 30,000 or so miles is when we reccomend a change where I work. We get some in with over 100,000 miles and a factory filter! Change it out for MPG and less stress on your fuel pump.

**FallenPhoenix** · Apr 23 2007, 03:58pm

Are all fuel filters pretty much equal, or is there as much room for quality variance as in oil filters?

**rubydist** · Apr 23 2007, 04:57pm

I disagree with the advice that your fuel filter can cause a decrease in mileage - I think the mechanic was right on with his statement that its impossible to have the fuel filter affect mileage.

The engine runs under closed loop 90+ percent of the time (unless you have a really heavy foot on acceleration) which means that the ecu is looking at the actual a/f ratio and adjusting it back to stoch. If the fuel filter starts to restrict flow, on a Ranger this will reduce the fuel rail pressure, slightly lowering the amount of fuel injected for the same injector pulsewidth. The ecu will see that the mixture is starting to be too lean, and will increase the injector pulsewidth to get back to stoch - none of which will hurt mileage.

The 10% of the time that the ecu is open loop, it will run a commanded a/f ratio. The ecu will look at the long term fuel trims to know what injector pulsewidth to run. There is no way a restricted fuel filter could cause this portion of the engine duty to be rich, but it could possibly cause it to be lean, if the injector is putting out less fuel than the ecu expects.

So, the reality is that there is no way for a restricted fuel filter to result in an engine that runs rich.

However, if you replace the restricted fuel filter with one that flows freely, it could cause the engine to run rich during the open loop portion of the duty, until the ecu re-learns the long term fuel trims (a couple weeks or less in most cases).

Now, a dirty fuel injector can cause you to lose mileage, because it won't put out the correct amount of fuel, so the O2 sensors will adjust for the average a/f on that bank, but you will be wasting fuel on 2 of the 3 cylinders (on a V6).

A bad O2 sensor can cause you to lose mileage, because it isn't reading the a/f correctly, which could cause the engine to run rich.

**Joe Turner** · Apr 24 2007, 12:30pm

Posted by FallenPhoenix

Are all fuel filters pretty much equal, or is there as much room for quality variance as in oil filters?

Yeah preety much.

Ruby, the results speak for them selves. Myself and many others have gotten better mileage when replacing a fuel filter. By saying that it doesnt affect mileage, may swing people not to replace it after all, causing more problems in future.

**budgie** · Apr 24 2007, 01:25pm

Whatever the case, it is a really good idea to change it so it doesn't lead to failure of your fuel pump (a ,uch more expensive part), thus not only leaving you stranded but handing you a much larger bill for repairs.

**RangerHaver** · Apr 24 2007, 02:12pm

I would have to agree with everything rubydist said.

**Jerry99Sport** · Apr 24 2007, 07:23pm

Hah, just when I start to accept one argument, an opposing one comes along that also makes sense.

With 34k miles now, I will probably get the filter replaced in the fairly near future. I don't know if the previous owner did it at 30k. But I can't help that thinking the 30k replacement interval is overly stringent/cautious. I have seldom heard of people replacing fuel filters that often on vehicles in general.

**Smashed96gt** · Apr 25 2007, 06:48pm

Ok the fuel filter itself may or may not hurt gas mileage. However when it can no longer trap dirt it will then get to the injectors and clog them affecting your fuel mileage.

**Jerry99Sport** · Apr 25 2007, 08:44pm

Posted by fordrngr

Ok the fuel filter itself may or may not hurt gas mileage. However when it can no longer trap dirt it will then get to the injectors and clog them affecting your fuel mileage.

I don't think a fuel filter will stop trapping dirt when it gets dirty. Instead, it will become too good at trapping things, including fuel. Someone correct me if I'm wrong.

**RangerHaver** · Apr 25 2007, 09:12pm

you are correct

**Spike-Hutto** · Apr 27 2007, 07:00pm

I've had my truck for a few month's now and I have discovered that the fuel filter has never been replaced! 1 fuel filter=107k miles? Ha ha. So I think I'm going to take care of that fairly soon.

**JDN2424** · Apr 27 2007, 08:16pm

To throw some fuel on the fire so to speak....some of the new Fords do not even have fuel filters. They have whats on the pump in the tank. I have not had one out yet but I assume it is just a sock......But you know what happens when you assume.

**dlibson** · Apr 27 2007, 08:55pm

First off, I can promise you a clogged fuel filter causes lower fuel economy.

If the fuel filter starts to restrict flow, on a Ranger this will reduce the fuel rail pressure, slightly lowering the amount of fuel injected for the same injector pulsewidth. The ecu will see that the mixture is starting to be too lean, and will increase the injector pulsewidth to get back to stoch.

This statement says what I said even though the person who said it disagrees. When the vehicle notices it starting to run to lean and it increases the pulsewidth, you lose fuel economy. It is richening the mixture. More fuel!!!

Also, the fuel filter is in the tank, it is a real filter. It is stupid that the manufacturers do this. I have installed in line filters on a lot of vehicles. Maintainence is much cheaper then repair!

**drews_ranger** · Apr 27 2007, 09:03pm

Posted by Jerry99Sport

Hah, just when I start to accept one argument, an opposing one comes along that also makes sense.

With 34k miles now, I will probably get the filter replaced in the fairly near future. I don't know if the previous owner did it at 30k. But I can't help that thinking the 30k replacement interval is overly stringent/cautious. I have seldom heard of people replacing fuel filters that often on vehicles in general.

Do it already, its only a few bucks!!! It's one of those things that HAS to be done. You change your underwear right? (we hope) Treat your truck the same man.

When I was young my neighbor had a lifted Toyota that he washed every morning before he went to work and I never understood it. He told me, you shower every day right... treat your truck the same. RESPECT PLAYAS!!!!

**Zoom** · Apr 28 2007, 07:23am

Posted by dlibson

First off, I can promise you a clogged fuel filter causes lower fuel economy.

This statement says what I said even though the person who said it disagrees. When the vehicle notices it starting to run to lean and it increases the pulsewidth, you lose fuel economy. It is richening the mixture. More fuel!!!

Also, the fuel filter is in the tank, it is a real filter. It is stupid that the manufacturers do this. I have installed in line filters on a lot of vehicles. Maintainence is much cheaper then repair!

Can we disagree with a disagreement?

When the engine increases the pulse width to get more fuel in, it's not actually getting additional fuel, it's just injecting enough to get the engine back up to stoichiometric. So as long as it can increase the pulse width enough to get the fuel it needs, it's still running the same mixture as it would with a clean filter/lower pulse width. Kind of like as the fuel pump wears and the pressure decreases, the pulse width increases to compensate. It happens automatically and you don't notice it.

Where a really dirty filter or bad fuel pump decreases fuel economy is when the ECU can't increase pulse width enough to compensate for it. It can't inject enough fuel to get complete combustion, so what it does inject won't combust and gets wasted. But by that time you not only have poor fuel economy, but also a bad miss in the engine.