Horrendous 3.8L Gas Mileage
03-03-2014, 06:20 PM
#11
Ok thanks..... I usually check the speedometer after against my GPS to see how close I am.
03-03-2014, 06:29 PM
#12
JK Enthusiast
Join Date: Nov 2009
Location: Christchurch, New Zealand
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Interestingly a couple of days ago here in New Zealand I received a letter from our government agency that deals with vehicle fuel economy. The letter was informing me that an incorrect fuel consumption figure was given to them by the Chrysler distributor (mines a 2009 I bought new) and it has now been updated. I have flicked an email off to the dealer to see if they had heard if Chrysler was going to recompense people for their extra fuel spend. Looks like Kia and Hyundai had to do this a while ago in the States. Will be interesting to see what the response is.
03-04-2014, 08:54 AM
#13
My 07 2dr JK started losing power and dropping to single digit MPG's in the city at around 30,000 miles. I of course assumed the worst and thought I had one of the dreaded "bad" 2007 motors.
Dealership was no help at all, I know shocker.
Did some digging on my own and found a couple things that were slowly killing my engine.
1.) Bad PVC valve, oil had been blowing back into the upper intake for so long it was full of sludge and slime. Replaced valve removed intake and cleaned the snot out of it.
2.) Bad spark plug gaps. All 6 were out of spec from the factory. All 6 had too large of a gap and 2 were worn. I put in new E3's. Idle and low RPM driving improved instantly.
3.) Combustion chambers were full of carbon. Looked like chocolate cake in there. 2 full cans of Mopar combustion chamber cleaner split between all 6 cycliners did the trick.
Used a long funnel to direct it down the spark plug holes. Smokes like a Cheech and Chong movie during application so go to a buddies house in the country to do it.
Changed oil, filter and checked plugs again afterward. Chambers looked surprisingly clean.
Tip, take the fender liner out of the passenger wheel well, gives you a straight shot at the hard to reach back plugs. Had mine out 3x before I was done so it helped.
Within 1 tank my MPG went back up to 15 in the city and regained lost horsepower.
Hope this helps or at least gives you something to look for.
Dealership was no help at all, I know shocker.
Did some digging on my own and found a couple things that were slowly killing my engine.
1.) Bad PVC valve, oil had been blowing back into the upper intake for so long it was full of sludge and slime. Replaced valve removed intake and cleaned the snot out of it.
2.) Bad spark plug gaps. All 6 were out of spec from the factory. All 6 had too large of a gap and 2 were worn. I put in new E3's. Idle and low RPM driving improved instantly.
3.) Combustion chambers were full of carbon. Looked like chocolate cake in there. 2 full cans of Mopar combustion chamber cleaner split between all 6 cycliners did the trick.
Used a long funnel to direct it down the spark plug holes. Smokes like a Cheech and Chong movie during application so go to a buddies house in the country to do it.
Changed oil, filter and checked plugs again afterward. Chambers looked surprisingly clean.
Tip, take the fender liner out of the passenger wheel well, gives you a straight shot at the hard to reach back plugs. Had mine out 3x before I was done so it helped.
Within 1 tank my MPG went back up to 15 in the city and regained lost horsepower.
Hope this helps or at least gives you something to look for.
03-04-2014, 09:25 AM
#14
JK Super Freak
Hey guys, my 2008 3.8L is averaging 10.7 and sometimes worse. Every once a while it'll jump up to 12.Somethin on the interstate crusing at 60. I live in South FL where traffic is horrible but I don't see my MPG being this bad.. I'm running a 2.5 inch RC lift on 35 KM2s. Do you guys think there is a reason for these MPG? Thanks!
03-04-2014, 01:10 PM
#16
JK Super Freak
Join Date: Feb 2009
Location: Pittsburgh, PA
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My 07 2dr JK started losing power and dropping to single digit MPG's in the city at around 30,000 miles. I of course assumed the worst and thought I had one of the dreaded "bad" 2007 motors.
Dealership was no help at all, I know shocker.
Did some digging on my own and found a couple things that were slowly killing my engine.
1.) Bad PVC valve, oil had been blowing back into the upper intake for so long it was full of sludge and slime. Replaced valve removed intake and cleaned the snot out of it.
2.) Bad spark plug gaps. All 6 were out of spec from the factory. All 6 had too large of a gap and 2 were worn. I put in new E3's. Idle and low RPM driving improved instantly.
3.) Combustion chambers were full of carbon. Looked like chocolate cake in there. 2 full cans of Mopar combustion chamber cleaner split between all 6 cycliners did the trick.
Used a long funnel to direct it down the spark plug holes. Smokes like a Cheech and Chong movie during application so go to a buddies house in the country to do it.
Changed oil, filter and checked plugs again afterward. Chambers looked surprisingly clean.
Tip, take the fender liner out of the passenger wheel well, gives you a straight shot at the hard to reach back plugs. Had mine out 3x before I was done so it helped.
Within 1 tank my MPG went back up to 15 in the city and regained lost horsepower.
Hope this helps or at least gives you something to look for.
Dealership was no help at all, I know shocker.
Did some digging on my own and found a couple things that were slowly killing my engine.
1.) Bad PVC valve, oil had been blowing back into the upper intake for so long it was full of sludge and slime. Replaced valve removed intake and cleaned the snot out of it.
2.) Bad spark plug gaps. All 6 were out of spec from the factory. All 6 had too large of a gap and 2 were worn. I put in new E3's. Idle and low RPM driving improved instantly.
3.) Combustion chambers were full of carbon. Looked like chocolate cake in there. 2 full cans of Mopar combustion chamber cleaner split between all 6 cycliners did the trick.
Used a long funnel to direct it down the spark plug holes. Smokes like a Cheech and Chong movie during application so go to a buddies house in the country to do it.
Changed oil, filter and checked plugs again afterward. Chambers looked surprisingly clean.
Tip, take the fender liner out of the passenger wheel well, gives you a straight shot at the hard to reach back plugs. Had mine out 3x before I was done so it helped.
Within 1 tank my MPG went back up to 15 in the city and regained lost horsepower.
Hope this helps or at least gives you something to look for.
03-04-2014, 03:06 PM
#17
JK Newbie
Join Date: Oct 2013
Location: Tahoma, CA
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My 2009 JKUX is getting 17-18mpg with 35" tires (Duratracs) and 5.13 gears. It's pretty light right now without a spare and I have a new front 75lbs bumper on order. Will be interesting to see how much it will affect my mileage.
I live at 6200ft elevation, and usually turn off my OD on the 2 lane roads up here in Tahoe. Also, my commute is about 20 miles RT on a 40mph road, which I'm sure helps.
I've been pleasantly surprised.
I live at 6200ft elevation, and usually turn off my OD on the 2 lane roads up here in Tahoe. Also, my commute is about 20 miles RT on a 40mph road, which I'm sure helps.
I've been pleasantly surprised.
03-05-2014, 06:30 AM
#20
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Join Date: Apr 2010
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Hey guys, my 2008 3.8L is averaging 10.7 and sometimes worse. Every once a while it'll jump up to 12.Somethin on the interstate crusing at 60. I live in South FL where traffic is horrible but I don't see my MPG being this bad.. I'm running a 2.5 inch RC lift on 35 KM2s. Do you guys think there is a reason for these MPG? Thanks!
rock
