Guns & Outdoors Forum

Since clubhouse was not getting much interest lately here is my latest test

A few weeks back it was time to replace the engine air filter on the honda. 4 cy 1.5L turbo

The closest auto parts store only had STP filters in stock for the honda. So i got one installed it and boom! Gas milage instantly dropped by almost 10%. First I thought it must be hot summer gas in AZ so i looked up the expansion of E10 blend regular and no way will this make that kind of difference at 110 degrees and the the temps had been high the weeks before and the mage stable for years. What changed? Ahhh new air filter

So i ordered a new Fram installed it at the end of the second tank milage is right back to where it was before

Damn! Never thought of that…

Never crossed my mind either. I use OEM in the Toyota.

Need to check this out. 10% is significant. I know that anytime I change filters I get a bump on mileage but I always just assumed it was because my filters get very dusty from desert trails. Never thought change from one brand to another would make a difference.

The old dirty filter was about 34.5 mpg. The STP filter was at 31.2 after a couple tanks of gas.

The difference is the STP filter is more restrictive but catches more and finer debris. So its a trade. The performance filters do let a lot more fine grit through and are way expensive so i just went to a major brand i have used before.

Your milage may vary and small displacement engines may be impacted more than larger engines. The honda is 1.5L thats about 100 CI.

Project farm just posted a test of 15 different brands of air filters 5 days ago
https://youtu.be/1PA8AHGJMPQ?si=Jm8j3Jg6I5NKmQ0S

GrapeApe wrote: ↑Wed Aug 26, 2026 7:48 pm Project farm just posted a test of 15 different brands of air filters 5 days ago
https://youtu.be/1PA8AHGJMPQ?si=Jm8j3Jg6I5NKmQ0S

GrapeApe That is an impressive test!
of course it came out after I put in one of the lower rated filters! i didnt research, just went with a familiar brand when i changed it.
but my mileage is back to where it was.
After a bit of reading the truck folks are not happy with STP either
i dont remember what filter was installed prior to the STP

I run K&N air filters in my vehicles...a bit pricey but its the last air filter you're going to buy for a long time...