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-   -   Mileage drop (http://www.jeepgarage.org/f5/mileage-drop-17536.html)

fenner408 01-16-2011 03:59 PM

Mileage drop
 
Hey guys, so the wifes 05 WK 5.7 was gettin 15-16mpg with 235/60/17s on it. I put on 255/65/17s on it, replaced plugs (Champion platinums), and installed an Airaid Jr. kit, and replaced an O2 sensor. Now its getting 12-13mpg. This seems low to me but Im new to Mopars. Any ideas would be great.

lll2for3lll 01-16-2011 04:17 PM

Re: Mileage drop
 
Maybe because you did an intake and no exhaust. Sucking in a lot but can't get rid off it.

Just a thought. I don't know but maybe.

jeepgcoman 01-16-2011 04:51 PM

Re: Mileage drop
 
Perhaps it's the change in tire diameter making the odometer read wrong.

fenner408 01-16-2011 07:12 PM

Re: Mileage drop
 
Quote:

Maybe because you did an intake and no exhaust. Sucking in a lot but can't get rid off it.
Ive never hear of an intake hindering mpgs. Does exhaust make much difference on these.


Quote:

Perhaps it's the change in tire diameter making the odometer read wrong.
I got the speedo recalibrated at the local dealership. They could only go to a 245/65 but that should only be a minimal difference.

lll2for3lll 01-16-2011 07:27 PM

Re: Mileage drop
 
It's better to do exhaust along with intake. It was just a thought though. But you will have many people say do both together.

Also, 65 profile tire is OEM for WK's. Who put 60 on there?

jeffs3232 01-16-2011 09:16 PM

Re: Mileage drop
 
Plat. Plugs on a Hemi? That's a no no. They take copper.

SvenskaJeepGuy 01-16-2011 10:49 PM

Re: Mileage drop
 
you have to use Champion 570 copper plugs

dmsfun 01-17-2011 05:34 PM

Re: Mileage drop
 
Copper plugs only in the Hemi; platinums do not have as hot of a spark. You may notice a misfire in the near future. The larger tires are causing the reading to be off a bit, and also are much heavier, by around 6-8 pounds a piece I would estimate, which is unsprung weight. Larger diameter tires also changes gearing, making accelleration slower.

fenner408 01-18-2011 07:28 PM

Re: Mileage drop
 
will copper vs platinum make that much difference in mpgs.

that small of a tire change shouldnt make a 4-5 mpg loss.

it had 65s not 60s my bad.

SvenskaJeepGuy 01-18-2011 07:39 PM

Re: Mileage drop
 
yes, switch the plugs again

05wkguy 01-18-2011 09:19 PM

Re: Mileage drop
 
Plugs and tires are your culprit. Changing back to copper plugs will regain MOST of what you had but it will never be the same with the larger tires. Typical loss is 1 to 1.5 mpg in town.

2005JGC 01-19-2011 02:23 AM

Re: Mileage drop
 
Yeah, at 245/65 your 1.7% under, so according to my calculations, a whopping .08% or your fuel economy loss is due to just poor calculation ;)

As others have said, heavier unsprung weight, and wrong spark plugs... ALL mopars are pretty picky about plugs, for future reference, if you EVER get another one and decided to do a tuneup put nothing more and nothing less than the manufacturer specified plug... its a bummer bosch wont be getting rich off chrysler products any time soon :(


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