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Fuel mileage dropping???

13K views 38 replies 27 participants last post by  mathew85 
#1 ·
I have a 2012 JKU Sport 3.73 gears, automatic with 2.5" lift and 35" tires. Dealer did an update flash on the ECM and now my mileage has dropped to 14.7 actual or 15.4 EVIC on dash from 17.5-18 mpg since I bought it in July. Dealer says it's the colder weather not the flash. I was wondering if this mileage dropping is happening to alot of JK's, mine has just over 4000 miles on it.
 
#13 ·
My Hemi Grand drops 1-2mpg for the exact same trips winter vs summer. I count on 21-23mpg highway (long haul Chicago to Green Bay round trip) in the summer and it drops to 19-21mpg on winter blends. The range of mpg is due to the better non-IL gas I get in WI for the return trip. Needless to say that fuel can make a large effect on economy and performance.

Double-check your speed/odometer calibration and then run a few more tanks from a reliable high volume gas station. If no dice there, a fuel economy hit is related to an impending head issue, FWIW. Keep an ear on it.
 
#9 ·
Yes I have the Procal and im wondering the same thing. I did have to zero out my TPMS to zero again after the dealer flash. Speed seems right though. No head issues so far but im also wondering if this is a warning of an upcoming problem. Heading up north to deer hunt soon so I hope not.
 
#11 · (Edited)
winter grade fuel? educate me please... I thought all fuel was winter grade as it doesn't freeze until -40 to -50 C.

From what I always understood, the cold makes the tires harder, shrinks the air inside and you loose a couple pounds of psi. A couple pounds low will cause enough drag to cause the increase your seeing. Have you checked your tire pressures while cold? Seriously, 1 low tire by 3-5 psi can cause a decrease by 3-5mpg on average.
 
#16 ·
#12 ·
Winter is just a appetite for less mpg. I go from 16.5 all summer and already I'm pulling 14's now. Engine takes longer to get to operating temperature so it is not as efficient as a fully warmed up engine. Cold air is denser thus more is sucked into the engine which in turn burns more gas to compensate.
 
#24 ·
Hi everyone. I have a '12 JKU. I got it new last October ('11). I have 30000+miles on it. When it had 9000 miles I had to have a header replaced. Runs better since then. I typically get 19-21 miles/gal. When I drive on the hwy I get around 21-22. My problem is that all of the sudden I've been getting around 15 miles/gal and I have NOT changed my driving. In fact when I saw the milage go down, I started to drive even slower and tried to keep it down. I read someone ahead of me on this post say that the dealer said it was the colder weather? Is that what's going on? I have a hard time believing this because I had it last year and my milage was fine EXCEPT before I had the header replaced. It got better afterwards.
Any thoughts?
Thanks Misty
In totally stock

I posted this on a different thread too. Any help would be appreciated. I'm taking it in the shop tomorrow to check for a water leak above the passenger door. I have water in the floor boards and on the seat belt when it rains hard.
 
#25 ·
Has anyone tried the older trucker method of putting a piece of cardboard over the front grill to see if it makes any difference? I know it would be ugly and all, but I have heard it may help with gas mileage because your engine warms up faster and stays warmer longer between trips and it keeps the cold wind out. I don't know how true it is on Jeeps vs trucks though. I notice a 1-2 mpg drop in winter usually.
 
#28 ·
Truckers blanket their radiators for increased thermal efficiency, not for fuel consumption. Physically blocking a radiator makes the Diesel engine run hotter for the heater.

Gasoline engines won't benefit, except to warm up quicker due to a restricted radiator. A remote start option will do the same thing for a Jeep.

Both tractor trailers and Wranglers are horribly un-aerodynamic and increasing the physical restriction isn't going to help mpg.
 
#29 ·
Do not put a piece of cardboard in front of your radiator. It will not help with any kind of significance. A Diesel engine gets more efficient as it gets hotter. A gas engine blows up as it gets hotter.

The only benefit you will get from something blocking your grill is that you will make air pass around your jeep instead of into the engine bay. This in essence makes it more aerodynamic, but will cause more problems for you in the long run unless you have a way to remove the blocker when it gets hot. The new dodge is going to have flaps in the grill that will close when the engine is going and open when it needs the extra airflow for cooling.
 
#30 ·
I've seen this debated on all the auto forums I use. As brought up here winter fuel and drop in tire PSI seem to be valid points people seem to agree on.

One more is the cold start mode most modern engines seem to have. Until the thermostat reaches normal operating temperature, ECU's will run a generic tune which does not use feedback from the MAF and 02 sensors. This tune is usually richer than the one that kicks in once operating temps are met (I assume because the a/f ratio is not controlled by the ECU the manufacturers play it safe by keeping it rich.) People who drive short distances around town will see the biggest MPG hit in cold weather.

Of course I don't actually own a Jeep yet so I have not dug into the specifics of how the engine management works. I'm merely in the market right now...soon enough.
 
#32 ·
My '13 jku got around 19.8 after mods. Since then its dropped to 18.8 mpg for some reason. Im at 6800 miles.

Engines do lose mileage as they age but I wouldn't expect it this quickly.

I don't think winter fuel applies in southern Arizona, but who knows.
 
#35 ·
I don't think winter fuel applies in southern Arizona, but who knows.
I doubt it. Winter gas has more butane and other cheaper hydrocarbons in it. The reason they can add those in the winter is because it won't evaporate in colder regions like it would in the summer. Arizona is warm all year so I doubt you get any winer gas
 
#36 ·
I've had my 13 jk over a year now goin from 33's the first fall/winter an then 35's this fall an I have noticed once it gets colder outside around 40º an below gas mileage drops. I have went from over 19mpg with 33's an 35's to almost 17 in this past month or so. Its really not that big of a deal, gas mileage shouldn't be if you bought a jeep in the first place but like stated above I believe its because it takes longer for the engine to warm up an the air is much more dense creating more resistance on an unaerodynamic brick
 
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