Getting better than avg mpg (+10%). Something wrong?

[JEDI]

2005 mazda3i AT, 200k miles.

for years, 70% hwy/30% city driving = 33mpg.

the past 2 fillups I've gotten 36 + 37 mpg! I filled up at the usual gas station (costco).
I haven't gotten that good mpg since I bought the car new 9yrs ago.

i've done nothing different to the car and my driving has been the same.
no oil change and havent touch tire pressure since July. (and temps are definitely cooler now than in july.)

but I've been having problems w/my transmission though.. hard shifting from 1st to 2nd gear.
mechanic said the only fix is to replace/rebuild the tranny, else just drive it till it drops.

so is +10% better gas milage a precursor that my tranny about to die soon (ie: next week)?
If not, what caused this nice jump?

 

[Insomniator]

Do you like a grandma?

 

[JEDI]

Do you DRIVE like a grandma?

nope.. cruise control set to +13mph over the speed limit.

like I said, no changes to the car or my driving habits

 

[highland145]

non ethanol gas?

 

[cbrsurfr]

Did you stop using the AC?

 

[Belegost]

I would say the most likely is that you have adjusted your driving to accelerate less briskly from a stop to help avoid the hard shift from first to second.

 

[halik]

torque converter locking up ?

 

[ummduh]

Cars tend to run their best right before their demise.

 

[CombatChuk]

Winter blend of gasoline? Refineries typically add more ethanol during the summer season as a way to reduce emissions in those hot days...

 

[JEDI]

torque converter locking up ?

Explain?

Did you stop using the AC?

But how does that explain the previous 6+ years where I stopped using the a/c in oct yet mpg didn't increase to 36+ mpg?

Cars tend to run their best right before their demise.

yeah, that's what I'm afraid of.
thus this thread

 

[JEDI]

Winter blend of gasoline? Refineries typically add more ethanol during the summer season as a way to reduce emissions in those hot days...

again, how does that explain all the previous years when gas was switched over to winter blend and I didn't see an increase in mpg?

 

[CombatChuk]

again, how does that explain all the previous years when gas was switched over to winter blend and I didn't see an increase in mpg?

I imagine CostCo has some kind of arrangement with a type of OEM for gasoline for its' store. They may have switched to a different supplier that uses less ethanol hence why your mileage is up.

 

[LTC8K6]

IIRC, you were going to drive differently to help your transmission survive, such as taking off in 2nd gear.

You may be getting better mileage at the expense of what's left of your transmission?

 

[JEDI]

IIRC, you were going to drive differently to help your transmission survive, such as taking off in 2nd gear.

You may be getting better mileage at the expense of what's left of your transmission?

taking off in 2nd gear = better gas milage?!

and it damages my tranny by taking off in 2nd gear?!
how?

 

[LTC8K6]

taking off in 2nd gear = better gas milage?!

and it damages my tranny by taking off in 2nd gear?!
how?

Less revs from 2nd gear would burn less fuel, but you'd tend to have more slip from taking off in 2nd.

I dunno?

 

[Yuriman]

Have you been approaching lights slowly so you won't have to hit 1->2? That can save a ton of gas. You can think of braking as converting gasoline into brakedust, so any driving method to minimize using the brakes will save fuel.

 

[Midwayman]

taking off in 2nd gear = better gas milage?!

and it damages my tranny by taking off in 2nd gear?!
how?

My auto tranny does this by design in eco mode.

 

[MiataNC]

taking off in 2nd gear = better gas milage?!

and it damages my tranny by taking off in 2nd gear?!
how?

Taking off in 2nd could increase mileage.

Mazdas are setup with "Zoom Zoom" on throttle tip-in. Which basically means they will give better off the line performance at the expense of MPG. This gives a more sporty feel, but you won't get EPA estimated MPG if you don't granny the accelerator pedal. Starting off in second is most likely closer to granny-ing the pedal with regards to engine load and tip-in.

Starting in 2nd won't hurt the transmission. Heavy "lugging" isn't kind to the motor, but that won't be a problem unless you are starting from a dead stop on a steep grade.

 

[JEDI]

My auto tranny does this by design in eco mode.

Taking off in 2nd could increase mileage.

Mazdas are setup with "Zoom Zoom" on throttle tip-in. Which basically means they will give better off the line performance at the expense of MPG. This gives a more sporty feel, but you won't get EPA estimated MPG if you don't granny the accelerator pedal. Starting off in second is most likely closer to granny-ing the pedal with regards to engine load and tip-in.

Starting in 2nd won't hurt the transmission. Heavy "lugging" isn't kind to the motor, but that won't be a problem unless you are starting from a dead stop on a steep grade.

thx.. never knew that.

wow.. +10% mpg starting at 2nd gear then going back to 'Drive'?!

 

[MiataNC]

wow.. +10% mpg starting at 2nd gear then going back to 'Drive'?!

Change in driving style, weather cooling down, possible change in seasonal fuel blends, etc, could all contribute to the +10%. It is most likely a combination of factors.

 

[xBiffx]

Correct me if I'm wrong but wouldn't spending longer time accelerating, i.e. "grannying it", mean less MPG? I mean, you don't get more MPG from the acceleration side of the equation, its from the deceleration (or coasting side) isn't it? At least one far outweighs the gains from the other as to make one almost insignificant, right?

I had always been told to get up to speed quick using maybe 3/4 WOT and then coast as much as possible when you are stopping. Also you obviously don't want to be driving with two feet either and rubber banding it all over the place.

 

[MiataNC]

Correct me if I'm wrong but wouldn't spending longer time accelerating, i.e. "grannying it", mean less MPG? I mean, you don't get more MPG from the acceleration side of the equation, its from the deceleration (or coasting side) isn't it? At least one far outweighs the gains from the other as to make one almost insignificant, right?

I had always been told to get up to speed quick using maybe 3/4 WOT and then coast as much as possible when you are stopping. Also you obviously don't want to be driving with two feet either and rubber banding it all over the place.

My new Mazda6 has a "current mpg" display on the dash. If I granny drive it I never drop below @10-15mpg from a dead stop. Getting on the gas drops me to 4-7mpg.

I usually granny for one tank, and then drive it like I stole it for the next. My average mpg doing the same commute every week (70city/30 highway) is @31.5mpg (granny) and @28mpg (stole it). Right around a 10% difference.

Anecdotal I admit.

 

[xBiffx]

My new Mazda6 has a "current mpg" display on the dash. If I granny drive it I never drop below @10-15mpg from a dead stop. Getting on the gas drops me to 4-7mpg.

I usually granny for one tank, and then drive it like I stole it for the next. My average mpg doing the same commute every week (70city/30 highway) is @31.5mpg (granny) and @28mpg (stole it). Right around a 10% difference.

Anecdotal I admit.

Those meters aren't the whole story. They give you instantaneous MPG.

Accelerating lowers MPG, right? Therefore, if you spend more time accelerating, your MPG isn't going to go up, right? Plus, looking at only acceleration is showing you the least significant component of increasing MPG, is it not?

 

[MiataNC]

Those meters aren't the whole story. They give you instantaneous MPG.

Accelerating lowers MPG, right? Therefore, if you spend more time accelerating, your MPG isn't going to go up, right? Plus, looking at only acceleration is showing you the least significant component of increasing MPG, is it not?

I was just describing a scenario where you would see an 10% increase in mpg with only a change in driving habits. As you point out there are lot of things you can do to increase mpg.

With regards to time and acceleration, It really comes down to how much more time are you spending accelerating?

If you spend 2x longer accelerating, and your car gets 2x the mpg, your average mpg would be the same. If you spend 1.5x as long at 2x the mpg, you would see an increase in mpg. If you spend 3x as long at 2x the mpg, you would see a decrease.

Obviously that is an over simplification based on the fact that there are far too many variables to take into account.

 

[Belegost]

Those meters aren't the whole story. They give you instantaneous MPG.

Accelerating lowers MPG, right? Therefore, if you spend more time accelerating, your MPG isn't going to go up, right? Plus, looking at only acceleration is showing you the least significant component of increasing MPG, is it not?

His second paragraph gives his differences in average over a tank, which he estimates around 10%.

This is about inline with what I notice on my car as well. I have a cruise/sport selection for the AT, in cruise it accelerates from a stop in second and does not use aggressive down shifting when I let off the gas. Using sport mode I'll average around 25MPG on a tank with my normal commute. Switching to cruise mode that goes up to around 27MPG.

One thing about accelerating with an AT is that the torque converter is non-linear (even before discussing lock-up) so depending on the TC design there will be a different optimal acceleration curve for fuel efficiency, but this is not likely to be strong acceleration where the torque multiplier is high and the converter is not highly efficient.