My MPG is gone to crap

[zigger21]

I purchased a 2005 Bonneville GXP in August 2010. Right away I tuned the car up, I replaced the plugs and wires, change the air filter to a K&N cold air intake(the type where you remove the air filter assembly box and replace it with piping and a 4 inch Filter) I also replaced the fuel filter. I also ran fuel injector cleaner through it a couple times. Changed Oil over to Mobil one synthetic 5W-30. Lately Ive noticed that my MPG is at 19 to 20 MPG driving on the hi-way at 70MPH. It used to get mid to upper 20's. Granted we have winter setting in and the temperature is in single digits but I thought the cold air would help. Am I missing something or is there anything I could do to increase my MPG? Any help will be much appriciated. Take Care. Jonathan

[01bonneSC]

Cold air helps for horsepower but not so much for MPGs. Have you checked your tire pressure? PSI in them drops when the cold air comes around(contracts the molecules).

[sonoma_zr2]

where are you located, winter fuel blends decrease mileage. X2 on tire pressure. cold temps cause air to shrink, making tires under inflated. this increases rolling resistance, hence lower mileage.

[00Beast]

It's the winter blend fuel. Makes mileage go to crap.

I wanna know is how you drive your GXP where you get anything better than 21 MPG. No matter how much we baby ours, it only gets 22 max.

[1fatcat]

If you can get a hold of a scan tool that reads live data, check the fuel trim values. Short term can vary, but long term should be +5 to -5, with an ideal value of 0. Make sure your not using E85 fuel.

[dpnewfie]

My average mpg is 21.7. Keep in mind that 95% of my driving is at highway speeds (70+mph).

I would like to see this cold air intake setup you have and I noticed you said you changed the plug wires......was this a typo?

[mike2fix]

It's the winter blend fuel. Makes mileage go to crap.

I wanna know is how you drive your GXP where you get anything better than 21 MPG. No matter how much we baby ours, it only gets 22 max.

This was my thought, my 2005 with 65000 miles got 23-24MPG once or twice, on a long trip just freeway driving. Typically gets 18-20 while in heavy freeway traffic, around town with almost no freeway driving, it has dropped to 15-16ish MPG. I don't beat it like a drum, but I am no grandma driver either. I have had this car for 3-4 years and the mileage has always been consistent.

Not saying it isn't possible but I have never seen or heard of a GXP getting anywhere near upper 20's MPG.

[05gxp]

It's the winter blend fuel. Makes mileage go to crap.

I wanna know is how you drive your GXP where you get anything better than 21 MPG. No matter how much we baby ours, it only gets 22 max.

This was my thought, my 2005 with 65000 miles got 23-24MPG once or twice, on a long trip just freeway driving. Typically gets 18-20 while in heavy freeway traffic, around town with almost no freeway driving, it has dropped to 15-16ish MPG. I don't beat it like a drum, but I am no grandma driver either. I have had this car for 3-4 years and the mileage has always been consistent.

Not saying it isn't possible but I have never seen or heard of a GXP getting anywhere near upper 20's MPG.

X2!

[yonkerse]

My car isnt a GXP by any means (other than styling...kinda) but i have noticed a decrease in MPG (prolly 15-20%) recently as well. In addition to applying what all the others have said, I would remove your Cold Air Intake for the winter months. I have had a cold air intake installed on my car, and with my scanguage reading single to low double digit intake temps, I was skeptical. This past weekend, i put the original intake back in (complete box and all) and intake temps have been much warmer (50 degrees) when car is warm. I have noticed this helping my fuel economy greatly. I'm not back to summer MPG, but only seeing about 5-10% decrease MPG now.

And when installing your box, i sure hope you have a heated garage or something because installing my box in 15 degree weather was a trick when that rubber is so stiff! haha

[repinS]

Warm-up times in the cold weather will obliterate your mileage.