I wondered if there was a website somewhere that shows how small a specific fuel filter filters. The reason I want to know is I have an inline going from my auxilary tank to my main tank. I want to know if it is filtering finer than my trucks primary or if not I am considering doing the diy fuel filter.

As best as I can determine the stock filter is 10 microns I am adding DIY filter for ALX tank filtering at 6 microns and am planning on running all fuel alx tank

The Wix/Napa brand is rated at 4um nominal.

I run a Napa 3023 inline between my auxiallary tank and the main tank. Is there a way to find out how small it filters?

Go to wixfilter website, add a 3 in front of your Napa Part No. so it becomes 33023. You should be able to find the spec.

Thanks, I found it at fleet filter. 13 microns.

If you look up the ISO standard for particle measurement you will see that they recently changed how they measure the particles. The re-defining tended to bring the lower end up (4 became 6) and the higher end down (25 became 18) [examples]. Some companies still go by the old rating, but by anyones measurement no one really know a precise way of measuring particles below 4-5 microns. However, @ 5 microns they can get 95+% efficiency so they extrapolate that they are gonna stay pretty high when they go to 4, 3, 2, etc.

Some may say they are 2, 3, 4 micron filters, but dump in some ISO testing dust in that range and you will likely find yourself in need of new injectors and a pump.