K&n air filter lost some gas mileage

[Elkman]

The OEM air filter is going to be as good or better than a K&N unless you spend a lot of time driving on dirt roads or trails. It takes power to move the truck and it takes fuel to generate that power. It also takes power to accelerate the truck and to keep it moving with most of the fuel used to overcome air drag which in turn increases with the square of the truck's speed. At 60 mph the air drag is 4 times as great as at 30 mph.

With any new truck I spend time at various speeds on the highway to find the sweet spot where it gets the highest mpg. With my diesel 2500 truck it is at 62 mph. With my gas powered full size SUV it is at 55 mph (though it is 40% greater than the heavier and far less aerodynamic diesel truck). The SUV fuel economy is anywhere from 16 mpg to 34 mpg depending on the speed and how much acceleration is done. I average 22 mpg with my own mix of driving. I do avoid being stupid and driving faster than I need to as much as possible. No need to drive at 75 mph for a 15-20 minute trip someplace.

The diesel truck's fuel economy ranges from 10 mpg when towing a camper in 20 mph winds at 65 mph to 22 mpg when driven at 62 mph with no wind and no camper. The overall mpg has averaged between 16 and 18 mpg with normal use and a mix of in town and highway driving. I avoid making short trips with the diesel truck as it is hard on the engine and hard on fuel economy. For short trips where I do not need cargo space I drive a Prius that averages 44 mpg.

There are no magical solutions to improving fuel economy, only good driving habits. The big rig drivers with the identical trucks pulling identical loads on the same route can get 8 mpg or 10 mpg and the difference is 100% with the drivers. Freightliner and the other truck manufacturers are trying to use smarter engine and transmission control systems to turn more 8 mpg drivers into 10 mpg ones but these systems can only do so much to compensate for the skill and intelligence of the driver.

 

[50BMG]

So I installed a drop in K&N air filter in my 2014 Ram Regular cab 5.7 Hemi 4x4 and my gas mileage seemed to get worse! Whats the best option to increase my gas mileage?

OK, this is going to sound stupid at first, but for the summer time (you are in MI. too right? So only do this when the weather will be consistently over @45-50 degrees F minimum) run 10W-30 oil instead of 5W-20...

I personally have experienced about 10% better mileage when I run 10-30 than what I get when running 5-20 oil.
Honestly, I've tried it every way from Sunday to dis-prove this, and I keep getting the @ same results (8% to 10% better mileage with the thicker oil). So, for city driving, you'll probably get @ 1.5MPG better mileage.

I've talked to FCA, Ford & even Chevy engineers about this (one advantage of being in the Motor City; these guys are your neighbors) and the only thing we all can come up with is that the thicker oil has a better lubricant film on the engine parts (both when warm and at cold start) so the internal engine friction is lower.
Again, since the oil ports in the engine are designed for 5W weights, in the "colder than a well digger's a$$ in January"/winter weather is upon us, which is the only time when the "W"/dual viscosity thing is actually doing something for you, ALWAYS run the thinner/suggested weight oil.
BUT, when the weather is above 45-50F all the time, the "W" thing isn't really doing crap for you anyway, so why bother?

 

[50BMG]

I had to pass a few big rigs today coming home and buried the gas pedal for the first time since I installed my K&N CAI and my truck cut out when the RPMs got what seemed like 4500K ??
Scared the crap out of me....lol I thought I done flattened the cam our something?
Do ya'll think unplugging the battery and reseting the ECM would help?
The Chevy mechanic across the street said I'm probably getting too much air to gas ratio and the computer does this to keep too much gas going into the piston???

Were you going pretty fast at that time (like 115MPH+)?
I have a 2016 and I think I discovered my truck is electronically governed to @115MPH. Which it doesn't "shut down" entirely, it behaves like it does when you peg the gas pedal to the floor in park/neutral; a rev-limiter kicks in and that's about as fast as she'll go...
My old 2005 would go @125, I think? (in case the insurance man is watching... LoL...)

 

[boblonben]

So I installed a drop in K&N air filter in my 2014 Ram Regular cab 5.7 Hemi 4x4 and my gas mileage seemed to get worse! Whats the best option to increase my gas mileage?

Same situation on my 2017. But after reading up more and all I switched to an AEM filter and recovered probably just at 1 mpg improvement over the original filter set up. But we have to remember anytime we add MORE air flow thru the intake there will be MORE gas injected to keep the mixture in the proper range. K&N are more about HP/torque increases than mileage gains, even though if you have an educated foot you can get some mileage increase. Did the same thing with my Dakota 4.7L AEM worked better overall for mileage and performance.

 

[Eric Grayson]

Were you going pretty fast at that time (like 115MPH+)?
I have a 2016 and I think I discovered my truck is electronically governed to @115MPH. Which it doesn't "shut down" entirely, it behaves like it does when you peg the gas pedal to the floor in park/neutral; a rev-limiter kicks in and that's about as fast as she'll go...
My old 2005 would go @125, I think? (in case the insurance man is watching... LoL...)

Nope I was running about 60 and happened before I got to about 75... took a nose dive till I let off of it.

 

[docwho]

I didnt have a difference either way.

 

[boxofrokx]

On a closed loop, efi fuel system, getting better mileage from a freer flowing air filter defies any logic I have been able to come up with. At least at partial throttle. The argument for the free flow increasing power makes sense. However, at partial throttle the restriction is the throttle plate, not the air filter. With a carb engine, sure. It will change the air fuel ratio, but not in efi.

 

[slacadjuster]

Take your foot off the gas???

LMAO, yup, my sentiments exactly.