Curious MPG increase

[yippeekyaa]

Did the 5k oil change on the Vibe and logged the service in the fuel/maint. log in the glovebox. Took note of the MPG as of late. It's the wifes car and i barely drive it. Over the last 2 months the mpg average has gone up to 34 from 32. Nothing has been changed on the car. Same tires, air pressure, fill ups done at same station. Pretty much everything by the book and normal. So I asked the wife about it and she told me what she has been doing. She has been alternating between super and mid grade on each fill up. IMPORTANT NOTE HERE: It's a GT model. I'm thinking wow, 2 MPG increase and a bit of pocket change saved every other fill up. But just over 8k miles using this method and the range between fill ups has gone from 320 average to 370 average each tank. Should i be worried?

[RIT]

Yes you should. At this rate, by the time you have 60,000 your car will probably be making gas, instead of using it, and if you leave your gas cap on, it is liable to explode. You better be careful. Just kidding, of couse. This is probably just an anomoly in your data. Collect it over a longer period of time, and see what happens.

[Digger]

If this hold up try mid grade. It is a mix of 89 and 92 at the pump. Stations only have low and high grade fuel. the plus grade is mixed at the pump.

[joholste]

actually after the break in 5000 miles it's normal to have an increase in gas mileage.

[KNINE]

I've noticed tha my gas milage has gone increased by as much as 4 mpg since the weather is warmer.

[goodvibe]

3 things come to mind. If winter gas is used in your area, the mileage will suffer during that period and show an improvement when summer formula is reintroduced. If she was normally using midgrade and is now raising the octane in her recent fills, the added advance could show an increased efficiency. You didn't mention the overall mileage in the car but rings seating can give more effisiency also. Could be any or a combo of the 3 but this motor is pretty tight out of the box so I suspect it's a gas issue. There's no magic here and there sure isn't anything to worry about

[NUBlackshirts]

He's in North Carolina....don't think they have Winter gas there. Not like here in Colorado anyway.

[yippeekyaa]

The car is an 03 GT with current odo of 113k. Went back and looked and the range per tank jumped suddenly on Feb, 21st at the 104k mark and has stayed high since then. So 9k miles of doing this with a near constant range in the 370 to 390 mark. 2 fillups went just over 400 and the lowest range was 368. That was the only sub 370 range fill up.A check of older data shows a steady 325 to 340 range.The only thing that has changed is the alternating between super and mid grade on each fill up.

[Tubaryan12]

my gas mileage usually goes up a little with a fresh oil change as well.

[goodvibe]

Quote, originally posted by NUBlackshirts »He's in North Carolina....don't think they have Winter gas there. Not like here in Colorado anyway. It actually can get down below 0* in parts of North Carolina and low teens are common in the coldest months. That's winter gas temps if you want your car to start and the oil companies have to plan for worst case situations. There winter gas season is just shorter so seeing an increase at the end of Feb may fit here nicely. As I suspected it obviously wasn't break in.

[jake75]

Quote, originally posted by Digger »If this hold up try mid grade. It is a mix of 89 and 92 at the pump. Stations only have low and high grade fuel. the plus grade is mixed at the pump.Seems to me that the grades here are 87, 89 and 91 (or 92) octane. The price bump used to be a dime each but now I think it is often more. I suppose auto supply stores sell octane booster additives but I never looked. The gas compnaies infer that their highest octane has more cleaning additives - don't know if that is real or if it is memorex. Giant Eagle has a 20 cent a gal discount for each $50 purchase. Gift cards count. Bought some hotel and Cracker Barrel gift cards for a recent trip. Got a 17 gal "87" fill this week for 1.42.9/gal and my cc gives me a 5% discount off that.

[drunkenmaxx]

i say chalk it up to warmer weather = better MPG

[NUBlackshirts]

Quote, originally posted by goodvibe » It actually can get down below 0* in parts of North Carolina and low teens are common in the coldest months. That's winter gas temps if you want your car to start and the oil companies have to plan for worst case situations. There winter gas season is just shorter so seeing an increase at the end of Feb may fit here nicely. As I suspected it obviously wasn't break in.Wow! Didn't know it got so cold there. Heck, that's worse than here in Denver! We get the cold, but usually not THAT cold. Wonder if it has to do with the almost zero humidity here? So, the winter gas thing does take effect there. And, with 113,000 miles on the odometer, it DEFINITELY isn't "break-in".

[Whelan]

I do my oil every 3k. But I also drive approx almost 2,000 miles a month or more. So to go 5k between changes would not make sense. They rate the 5k oil change based on the lease terms of 12-15mos. Which does not equal a lot of driving for me at least. I started the beginning of this year with just a hair over 40,000 miles on the ticker. So far I'm at 51k. So in 6 months 11,000 miles.

[yippeekyaa]

Somehow i knew someone couldnt leave the 5k oil change interval alone. Mobil 1 and pure 1 filter. Nuff said as this thread is not about oil change intervals. you do it your way and ill stick with mine thank you very much.

[engineertwin2]

Quote, originally posted by Whelan »I do my oil every 3k. But I also drive approx almost 2,000 miles a month or more. So to go 5k between changes would not make sense. They rate the 5k oil change based on the lease terms of 12-15mos. Which does not equal a lot of driving for me at least. I started the beginning of this year with just a hair over 40,000 miles on the ticker. So far I'm at 51k. So in 6 months 11,000 miles. Actually, I thought that the OCI's were dependent on type of driving. Per my manual, it varies between 3,000 mile to 7,500 mile interval, dependent upon whether you drive all city or all highway.I'd say if you are putting on 2,000 miles a month and not in a lot of hard acceleration, you should be more than comfortable to extend out the OCIs to 5,000-7,500 miles. I currently send oil samples out for analysis at 2,500 mile intervals and have changed between 5,000 and 7,500 miles. Of note should be that the oil analyses have always come back as being in good condition. I always stick with Mobil 1, but wouldn't hesitate to keep up the gig with plain ol' dino.Remember, the 3,000 mile OCI is based on older engineering, when seals weren't as tight and oil's weren't a) as pure, and b) multi-viscosity.