rx280

I’m wondering whether anyone else – especially people in this part of the country (New England/the Northeast) have noticed a fuel-economy drop-off in the last month or so.
I compute my mpg at every fill-up, and my average in November (4 fill-ups) was 26.3. For the purposes of comparison, my October average (4 fill-ups) was 28.5, and I've averaged right around 28.0 in the 37 months I've had the car ('04, 6MT).
The November dip isn't huge, but it still had me wondering about a possible cause, so when I was at my local dealer last week having the audio module replaced (to address the dreaded audio-HVAC display dim or dark problem), I asked the service manager what the reason might be. He immediately blamed “winter gas.”
He said something to this effect: with gas now containing ethanol (10%), the additives package had to be adjusted for winter, or at least adjusted differently than in late autumns past, and engines don’t run as efficiently on the new formulation. He claimed that some cars – Acuras, presumably, but he wasn’t specific about year and model – had to be towed to the dealership because they were running so poorly.
Needless to say, I was dubious about that story, which may have been intended to make me think that a little drop in fuel economy was a minor matter compared with what some other Acura owners had experienced lately.
So, anyone else seen an mpg dip, and any thoughts on this “winter gas” theory?

synthetic

I don't see why you completely ignore the cold weather and seek other reasons for your mpg drop. Winter gas is partly to blame(that's if your local gas stations have already switched to winter gas), but the biggest blame goes to cold morning starts and the car running slightly colder than it normally would.

Now you say you've driven the car for 37 months. I assume you've driven it during 2 other winters. It's very hard to achieve an average of 28mpg during a winter unless the vast majority of your driving is on the highway. Note that a slight change in your trip(a bit more of city driving) will have dramatic effects on your mpg during cold weather.

Other things you might want to consider as DELTA factors are:

1. the wear on your tires + tire pressure

2. The wear on your clutch-disc(which is surely not getting better) Although not a huge factor, it still has an effect on mpg.

3. road conditions.

and so on...


Again, for a drop of 2mpg, there's way too many factors that are playing against you here, and my first suspect would be the weather temperature. I have the 06 6MT with the MID(which shows the rate of fuel injection and average fuel consumption) and let me tell you, you'd be amazed at the rate of fuel-injection during cold starts. It pains me to see my mpg drop so fast when the car is driven cold.

Brandon24pdx

they put 10% ethanol in the gas around here starting November 1st believe to help cut emissions ("E-10 gas") Yes, it will lower your MPG a little compared to the pure stuff.

rx280

Responding to synthetic’s comments:
-- In Massachusetts, the month that just ended was one of the warmest Novembers since weather records started being kept, so I don’t think temperature was much of a factor. What got my attention was two consecutive 25-point-something fill-ups after averaging 28.5 in October.
-- I got the car in late October of ’03, so I’ve driven it in three previous Novembers and three winters. I didn’t experience an equivalent drop-off in November of ’04 and ’05. That’s one of the reasons I was wondering about a possible reason for the dip last month. (We can disregard November of ’03; the car was brand new.)
-- My driving is primarily highway – at least 75% – and always has been. I agree that your fuel-economy numbers will drop in winter conditions, probably by 1-2 mpg, but again, November this year was anything but wintry around here.
-- I check my tires regularly and keep them at 35F/33R; nothing’s changed there.
My reasons for posting the original msg were curiosity as to whether anyone else using gas formulated for conditions like New England’s had seen any sort of drop-off and a desire to get opinions on the service manager’s winter-gas explanation (and his story about ailing cars being towed in.)

jswim99

Here in Colorado stations begin selling oxygenated fuel in early Nov. and continue at least through March or April. I've noticed a consistent ~10% drop in economy in multiple cars through multiple winters. My drive is 80% highway (100 miles/day), and my car is garaged at one end of the commute, so I don't think the drop is all due to cold starts.

synthetic

Thanks for the clarification and sorry if my message came out a bit harsh(I had just woken up!)

In that case, I would be curious too. Another thing would be the air-filter?

psteng19

Dealer ain't spewing BS at you, it's true that winter blend kills gas mileage.

ChrismanTSX

The addition of Ethanol to regular gas will significantly lower your mileage.

Regular Gas has an Energy Density of 44MJ/kg, while pure Ethanol has an ED of 26.8. E10 (10% Ethanol, 90% gas) therefore should have roughly 42.3, equivalent to 96% of gas' ED. As such, this factor alone would contribute to a 4% decrease in fuel economy (or 1-2mpg).

Also, take a look at how much time you let your car idle. We tend to let the cars idle more in the cold (at a stellar 0mpg). Also, as the previous poster highlighted, running the engine cold uses more fuel, especially on short trips.

kyotousa

^^^^
but if you idle and wait for engine to warm up...it's still burning fuel
so just do a rolling warm up.......it all even out

i guess that's why i am getting 27hw....20 city

JTso

iTrader: (2)

The ECU is programmed to run slightly richer during cold start in warm up mode and continues to do so until the coolant temp has reached a certain degree (~175 F). Cold weather prolongs this process and will have an effect on gas mileage.

rx280

Just another clarification attempt:
-- I understand that, generally speaking, your mpg numbers will go down as the temperature does. (Bearing that out is my fuel-economy average from the last two Julys, 28.5, versus my average from the last two Januarys, 26.6; I did the calculating just now.) Again, though, the November we just had in these parts was a lot warmer than normal – more like a typical October, I’d say.
-- As for ethanol, it’s been in the gas here (at 10%) for quite a while now. I can’t recall precisely when we started getting it, but I’m almost positive it was before this past summer, and my mpg numbers from this summer look remarkably similar to the numbers from the previous summers.
I thought it was this that the service manager said that was most noteworthy: with gas now containing ethanol, the winter additives package had to be adjusted differently than in late autumns past, and engines don’t run as efficiently on the new formulation. That made me think that people in the Northeast (and maybe in similar climates) might see a bigger winter-gas effect this year than in years past.
Still, his story about cars needing to be towed in because of winter gas seemed pretty far-fetched.

DateTSX

its' normal. I went from 28mix and down to 22mix. And I get crappy miles per tank too. From 350 average to barely making 300 miles.

kyotousa

oh yah....i thought it was caused by over-oiled filter hahah
anyway.....good info
I am getting crappy city mileage......
all freeway mileage is still pretty good

studville

I was thinking about this just the other day. Thanks for posting.

I've noticed around a 4 MPG dip here.

Regular - 18.5 city; 24 mix; 34 (ALL highway)

Currently - Regular - 15 city; 20 mix; 28 (ALL highway)

The last figure is a bit lower because lately, in between cities, I've been trying to make good time, hence faster driving.

PS 06 TSX w nav

Newplay1

It dropped for me I drove maybe 90miles last week and its already at 2/3 on the gauge.