You can apply any number of mods in order to gain a mile or two per gallon. Of course your ROI will be a big negative, of course. So what is the point? The obvious stuff should be maintained; air pressures, tune up and your road speeds.
Because tests, at least some that I have read, have found that, although they flow more air, the K&N filters also let too much dirt and harmful stuff into your engine. They found that the stock filter does a much better job. Sorry, but I don't remember exactly who "they" were so I cannot provide a link.
Edit: Here is one source of information.
Having had several K&N filters in the past including in my current two vehicles, I am still to experience any problem whatsoever. And these are real world tests.
It does not increase mileage but it does increase airflow which can lead to increased power made by the engine.
The article provided is long on testing and short on useful conclusions. I do appreciate that at least he is a fellow engineer. His results were totally expected - more airflow is accompanied by decreased filtration. The question is how much decreased filtration is acceptable for the driving conditions encountered. That is where these tests fall down. To the poster above who designs for military vehicles - I agree that the K&N or similar high flow/low filtration filters are not a prudent choice. That is a different story for vehicles that operate in more benign environments.
To bring this back on topic for the OP - increasing mileage (towing our otherwise) will not come by using K&N filters. Using the proper tire pressures in both the TV and the RV, reducing weight if possible, slowing down and installing a chip (in my experience) will do the trick for an increase you can actually see.
Not advocating, just questioning.
My lovely and gracious wife
Maggie, our Yellow Lab
2007 Jayco Jayfeather EXP 23B
2008 Toyota 4Runner V8 Limited AWD
Getting into filtration is a little off topic but I will answer only because many of you asked.
Why won't I use a K&N filter?
Yes, they allow more air to pass thru to the engine, that is why you may get slightly better horsepower.
The truth off the matter is that in order to give you better air flow they sacrifice filter efficiency. Is a lot? NO. But it is enough.
Most people look at the big number when looking at efficiency (98% - 99%). What you need to do is look at the small number - what is left after the 98% - 99%. Answer: 1% to 2%. A 98% efficient filter pass twice as much dust to the engine as a 99% efficient filter. It goes not sound like much but it does add up and could cause damage to your engine.
These number do not change based on high or low air flow.
Truth be told most contaminates that enter your engine DO NOT get there thru the filter - they get there during filter service.
Almost all filter systems in vehicle have an indicator on them. I would suggest that you only change the filter when indicated. DO NOT change just because they look dirty. Believe it or not dirty filters filter better than clean filters! Filters get more efficient with age.
I have been in the filter game for over 30 years - horse power increases that hard difficult to notice if at all and MPG increases that don't justify the cost.
Feel free to send me an e-mail with your questions.
I like one guys post - MPG is what it is, fill it up, drive and enjoy.
I can't find it now, but I recently read a filter rating article with a rating chart that used oil contaminant testing and some other things. One of the reasons it gave for K&N and similar filters that need be oiled causing problems is that it's very common for people to over oil the filters.
There was something else about oiled filters that could cause problems too, something about maintenance or neglecting maintenance. The recommendation in the article was to use "DRY" filters for the most trouble free results over time.
Dodge Ram 1500 Quad Cab
Equal-i-zer Hitch US Navy Veteran
...One of the reasons it gave for K&N and similar filters that need be oiled causing problems is that it's very common for people to over oil the filters.
There was something else about oiled filters that could cause problems too, something about maintenance or neglecting maintenance...
The main issue is that over oiling the filters can cause oil to migrate dowstream to the MAF sensor fouling same leading to replacement. Of course when the MAF sensor fails it leads to the engine not running properly.
On the other hand if the owner knows how to properly maintain the filter this is not an issue, and the same oil that can migrate to the MAF sensor is now allowed to do its thing -- trap more dirt while allowing more airflow. As someone mentioned before, as filters get more dirty they actually filter more (good thing) but that also comes with reduced airflow (not so good for power).
2000 Blazer towing a 3600 lb hybrid trailer, getting about 14.5 mpg at 50 mph, mileage goes to 20 mpg if I can stay at 1600 rpm in 4th longer, drops to 11mpg when engine downshifts into 3rd and tach goes to 2100. Got the 14.5 going across rte 10W in NM and AZ, 100 degrees outside. Have diagnostic reader on my OBD port, so get immediate readings.
Running 50 lbs tire pressure in the Trailer and 40 lbs tire pressure in the Blazer.
Better free flow exhaust on a recent class (22000 lbs) A caused the Ford engine to run cooler. Use of a KnN type air filter and Banks exhaust increased mileage about .5-.7. Generally I get better mileage using my foot vs the cruise control.
I've given up on worrying what my fuel cost are going to be, it's just one of those necessary evils!
2007 Toyota Tacoma, Double Cab 4x4 Max Towing 6,500lbs GCWR 11,100lbs
2011 Jayco X20E, Pro Series 800lb Weight Distributing Hitch
Husky Sway Control Bar, Prodigy Electronic Brake Control
Towed up to the lake this weekend, first leg, got 12 MPG, and was very happy. Second leg, ran into high head winds, couldn't get the TV over 40 without it downshifting into 2nd! Needless to say, 12 MPG, dropped down to under 8. Some things are out of our control, and just need to be accepted. The weekend, was Fantastic, once the wind stopped.