So my on my fifth fill-up and I picked up 1.8mpg going from 5w-20 to 5w-40 in my 14 JK. I've run PUP 5w-20 and PP Euro 5w-40 since. I know this isn't a scientific long term experiment but I honestly thought it was going to go down at least a mpg.
Summer blend gasolines are now being dispensed.The weather got warmer. That's it. A little bit counts a lot.
Also, nice avatar.
Since sheardown is a real thing, that seems to jibe with the physics.my mpg was always best just before an oil change
Just from butt dyno - my Jeep loves 45°F air temps …outside air temp can and does play a factor in mpg change to increase.
Not likely....You eventually have to drive uphill to drive downhill..You spent more time driving downhill?
Because of the summer fuel and warmer temps...My wife experiences the same thing as you with the same engine. Her 2015 Wrangler calls for 5w-20. I change to 10w-40 during the Summers. She reports better mpg's with it also. Over 190,000 hard miles (high loads, high rpm's) and still works well.