My gas mileage is improving
 

My gas mileage has gone from 18.0 to 20.1 with no change in driving habits. Could it be the winter fuel blend? Always use the same brand of premium.

If you're in Houston, perhaps you are using the A/C less in the fall/winter?

I would think winter fuel would decrease your mileage, but not sure on that one.

I'll bet you are right on the AC. In summer it's just left on, now I cycle it occasionally. It's still usually on, but on a dry morning it's turned it off.

Don't summer gas blends have more Ethanol ?

For a point of reference in summer (hot as hell Phoenix) I get between 21 and 22.5 mpg. In mild weather it will move up to 23 to 24. Once it gets really cold (for Phoenix that's in the 30's in the early morning) it drops back down to 21 to 22.5. When it's hot it's the AC and when it's cold it just takes longer for the engine to warm up to an efficent operating temp. Throw in some more ethanol dependng on the blend being used in your area for the time of year and that will also impact mileage. I find how you drive it impacts mileage more then anything else. At the track I drop down into the low teens.

Yes. 7-9%.

Winter blend is more like 5%.

This is what I saw a couple years ago with my test kit. Easy to do.

MPG city highway elevation
 

I live in Colorado. My commute is 27 miles one way. I'm at about 6200 feet. My commute is all highway miles. I get between 28-31 depending if I have to puts around town before heading home. I have a 99 with the 2.5l and a 5 speed manual. The highest octane fuel I can get is 91 and it has up to 10% ethanol in it. I accidentally put 87 octane in once and it felt like I was driving a Honda Civic. The power drop was frightening. I added octane booster and kept adding 91 as frequently as I could to get that low grade stuff out of there.

Bringing back an old post...

I've noticed my gas mileage improving as well. But first...

I drive a 1997 Boxster, so I know many of you have a more powerful engine and different efficiency, but...

My daily driving is about 70% highway 30% city driving. Occasionally it will get closer to 50/50, rarely does is see more than 70% highway time.

I tend to accelerate moderately, get up to speed and cruise just at or slightly above the speed limit (posted 65mph). What is moderate acceleration? I typically shift just before it gets to be really "fun", say above 4500 RPM. Yes I know....that's why I define this a "moderate" as opposed to hard acceleration. At least once a week I will tickle the red line. It's a semi-daily driver.

Ok, now my baseline is out of the way....

I typically have been seeing 25.5mpg average on the tank and often up to 27.5. However, recently I've notice the milage has been ticking upward tank after tank. In fact, I have just a bit more than 1/4 tank remaining and I'm looking at 28.9mpg!

That's NUTS!!

As a result, owning this car seems a bit like cheating because I've got the cake and now I'm eating it!!

Now for a question....

Is the increase in mileage indicative of winter blend gas? Don't think so...shouldn't it work the other way around (summer/winter)? I still use the AC at times in the late afternoon. I live in AZ.

Thoughts?

Winter gas blends have less energy in them than summer. But not all locations do the switch and not all at the same time. On the car forums where fuel economy is the constant subject, you see this remarked about all the time. Some use fuelly.com to monitor every tank of gas since the car's second tank.

Yeah that doesn't sound like fun to me. I was just surprised my the improvement I've seen. It does not seem to make sense to me.

What I did leave out is that I have a 5-speed and during this time of "improved mileage" I've also been driving with the top down more. It's pretty much perfect in the Phoenix area now!!

So the improvement seems weird to me...hence the post.

Thx!!

I have a friend who has a immaculate restored 1936 Phaeton. It's like the one President Roosevelt drove, but without the levers Roosevelt needed. He only uses Marine fuel in the car to preserve fuel hoses, etc. Not saying to use it in the Porsche. But just a thought and the octane should be OK.

So no electrical load from fans, no parasitic drag from the A/C. Somehow I think the Kamm effect would help more with the top up than down though.

I'd envy you your weather but I've been in Phoenix too many times when the temp was over 100 after 8 at night to want to be there year round.

one must consider that these engines run more efficiently at cooler temps., i.e. cooler inducted air.

I'm wondering what method you are using to estimate fuel mileage?

Pump gallons/odometer is most accurate. If you are using the built in computer mileage gauge then be sure to reset it at a new tank of gas to get a good avg read.

Otherwise its just a cumulative average including the time it sits idling in the driveway, waiting to pick up kids after school etc etc and skews the results a bit.