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.
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.
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.
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
I use NGK 6987 with AMSOIL Air / oil Filters and Lubricants, After the change I gained 4 miles per Gal, also used the AMSOIL PI Gas additive( 4,000 miles) to clean up the system.
I bought a 1 owner 2005 Limited with 64,000 miles Dec 2010. It is still a baby.
I will be replacing the tires to 235/65/17 for better fuel savings. It has 245/65/ now.
Wait. Those tires will look incredibly small on there. I bought mine with 245's and put 235's on and I think that's why I went from 16-18 mpg to 11-13 mpg.
Also check to make sure there isnt a loose hose clamp on the intake; will cause poorer running and loss of mpg. I had the dealer replace plugs during servicing the first time, and my mpg were poor for a couple weeks because the intake hose clamps were not tightened down.
I went from 245's to 265's and went from 22-23 pmg down to 16-19 mpg.ALSO put on a 3 " lift. I have the diesel 3.0 but still lost some MPG. Looks makes it worth it!
I also got my speedometer recalibrated but I think chrysler told me they could only make it accurate up to 255's so I think I am still off at bit.
Do you have a GPS? I would get it up to speed (over 50mph) and check the MPH reading on the GPS vs your speedo to make sure that the shop that re-calibrated you was right. They may have screwed it up.
the speedo is accurate for 245s (as close as they could adjust). On my way back from KC i just got 16.7 mpg (hand calculated and adjusted). This was on straight gas (no ethanol) so that helps but, wondering if winter blend is hurtin it much.