I recently bought a K&N air filter for my car for increased performance, not the gas mileage, so I didn't bother to check it. However, about a week ago my dad got one for his '97 Suburban and the gas mileage dropped from 17.5 to 15.5 or lower.... I'm confused...???

 

It has nothing to do with the air filter. Either something else is wrong with the truck or his driving style changed. Simple as that.

 

yeah i agree, i cant see how the filter would cause lower gas mileage.

 

I don't get how a free-er flowing air filter would lower the gas mileage either, but this is what happened. My dad went and filled it up, and computed 17.5 mpg. He came home and I put in the new filter. It sat in the garage until we took off for about 200 miles of expressway/highway driving, filled up again, and got 15.1. Then drove it another 200 miles on expressways and highways and topped it off again and got 15.5. The only time we ever got below 16 is if my mom had been driving the beast around town. If anyone has any idea as to why this happened, please let me know.

 

put the original filter on it again and see what your gas milage is again, i bet it will still be in the 15 range.

it sounds like bad coincidence somewhere. maybe you unplugged or loosened something when you did the change over? check all your vacuum lines and plugs

 

I like the idea of trying the old filters to see what your gas mileage is. If it goes back up it could be that the computer has learned to take away fuel to compensate for the clogged air filter. You could disconnect the battery to dump the computers learned memory when you put on the K & N filters and drive it for to have it learn again and then check your gas milage.

 

Maybe you were driving at 80 on the highway instead of 65? If I'm in traffic on the highway, I'll get about 15 in the Durango, if the road is open, I get about 13... Same difference if there was a 20 mph headwind during the drive...