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Old 01-16-2011, 03:59 PM
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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.
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  #2  
Old 01-16-2011, 04:17 PM
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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.
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Old 01-16-2011, 04:51 PM
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Re: Mileage drop

Perhaps it's the change in tire diameter making the odometer read wrong.
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Old 01-16-2011, 07:12 PM
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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.
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Old 01-16-2011, 07:27 PM
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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?
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Old 01-16-2011, 09:16 PM
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Re: Mileage drop

Plat. Plugs on a Hemi? That's a no no. They take copper.
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Old 01-16-2011, 10:49 PM
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Re: Mileage drop

you have to use Champion 570 copper plugs
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Old 01-17-2011, 05:34 PM
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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.
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Old 01-18-2011, 07:28 PM
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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.
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Old 01-18-2011, 07:39 PM
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Re: Mileage drop

yes, switch the plugs again
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Old 01-18-2011, 09:19 PM
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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.
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Old 01-19-2011, 02:23 AM
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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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