Instant MPG Boost!

[944boy]

Now that I have your attention...

So as a background, I have done quite a few long trips in the Boxster. Hence why it has over 106K. Last summer I did a 6000 mi+ trek across country for my sisters wedding. As before with the cruise control on, roof up, strait flat road, two people and luggage I was never able to break an average of 30mpg. If I recall my best indicated was 29.8 or something like that.

Not usually I could care less about gas mileage, sometimes I see how low I can get it just for fun. But this was interesting. Recently I changed the clutch out and replaced the fluid in the transmission. This is the only change that I made since last summer. Same oil, tires, wheels, etc...

Last week I drove down to San Diego and back for the holidays. Again two people and luggage. On the way down I was driving like a total ass so I couldn't really call, however on the way back after a friendly reminder that it wasn't acceptable I found myself with the cruise set 70-75, top up and even with some varied driving and AC on I was still at 30.6 until I hit traffic.

After dropping my GF off in San Fran, I came back down the 101 cruise set at 70, AC off, just me, and was able to average 32.2! Not that this is earth shattering by any means but a larger difference than I would have expected for just changing the gear oil.

Now I do have to admit that I did not use the Porsche gear oil but a formula given to me by a highly regarded Porsche mechanic. So far into the 40's it still shifted just fine. I'm not here to start a war on fluids, I'm just stating that clean fresh fluid made a much bigger difference than I would have ever expected.



Oh and still not a drop of oil used between oil changes!

[Kenny Boxster]

I take it you used a thinner viscosity fluid than the the original trans-axle fluid. Thinner fluid = less resistance, more efficient. Do tell.

[Flavor 987S]

The answer is 5%.

During your summer trip, 93 or 91 octane in your area was about 9-10% ethanol.

When you did the trip last week, the same gas is now closer to 4-5% ethanol.

That's my guess from testing fuel this past winter/spring and summer.

[Kenny Boxster]

That would make sense but I've heard anecdotal reports that winter blend gasoline is actually less potent then summer and also less fuel efficient. So, I imagine in the summer this guy's mpg maybe be an additional .2 increase. Still waiting for him to chime in.

[thstone]

My first thoughts are that real world driving has too many variables that can cause the mpg's to vary, especially if you're trying to account for a few percent difference. You'd have to drive the same route at the same time of year in similar traffic with the cruise control set to the same speed in the same places to get an apples to apples comparison that would allow you to try to isolate the change in mpg due to the change in tranny fluid.

Whatever change that the trans fluid had on the mpg's is most likely masked by all of the real world variables that are probably much larger contributors to a difference in mpg.

[944boy]

So I cannot for sure say what the ethanol content of all the gasoline was for all those numbers. The trip this last week was all California 91 gas, presumably winter blend.

Back in WA I regularly filled up at a station that was 92 - ethanol free.

The cross country trip was gas from all over the place... could have been anything. 93 up to 10%

I agree that these numbers were pretty meaningless, wind factors could also throw it off that much. Next time I'll just put the top down and leave it in 3rd.

But since I drive the car quite often these were numbers that just 'felt' overall better than I had experienced before.

Now my bike still gets mid 20's lofting the front wheel down the back strait at Infineon...

[Kenny Boxster]

Indeed. Many variables of gas blends, and also tail winds would probably do a lot more than tranny fluid. I believe it's a combination of tail wind and non-ethanol gas in some places, rather than the fluid.

[ccstud17]

Originally Posted by Kenny Boxster

... also tail winds would probably do a lot more than tranny fluid. .

winner winner chicken dinner!

as all have stated too many variables, but as some one who has made countless road trips thru good ole Wyoming ( I live 30 miles away from Cheyenne) And wind is the #1 contributor to good or bad MPG. same car same gas stations on the same day same route, jsut one was made in the morning when it was calm 28 mpg, later in the day moderate wind 24mpg. no traffic anytime haha it is Wyoming after all...

wind has an exponential effect on mpg, punching a hole through 5mph wind is pretty easy at 35mph, but at 80mph a lot harder!

im just happy to hear someone properly taking care of their car with gear fluid changes

[BYprodriver]

Originally Posted by ccstud17

winner winner chicken dinner!

as all have stated too many variables, but as some one who has made countless road trips thru good ole Wyoming ( I live 30 miles away from Cheyenne) And wind is the #1 contributor to good or bad MPG. same car same gas stations on the same day same route, jsut one was made in the morning when it was calm 28 mpg, later in the day moderate wind 24mpg. no traffic anytime haha it is Wyoming after all...

wind has an exponential effect on mpg, punching a hole through 5mph wind is pretty easy at 35mph, but at 80mph a lot harder!
im just happy to hear someone properly taking care of their car with gear fluid changes

The same is true for still air, as speed rises so does wind resistance. This is why cars are designed to be so aerodynamic

[san rensho]

If you set the cruise to 50 mph you would get great MPG, but who wants to drive at 55?

[Perfectlap]

I have never been anywhere near 32 mpg.

Since installing Fabspeed, which has led to RPMs average of 4-5K, I doubt I go over 20mpg.

[Raider]

Wasn't it after he dropped off the girl friend that the gas milage came way up? Just sayin'......

[944boy]

Is that a valid reason for a breakup, Weight reduction? Probably not a good idea to tell someone who is athletic and only 110...

[dbear61]

Originally Posted by 944boy

Is that a valid reason for a breakup, Weight reduction? Probably not a good idea to tell someone who is athletic and only 110...

Your GF is 110 years old?

[san rensho]

Originally Posted by dbear61

Your GF is 110 years old?

Dude, she weighs 110 pounds and works out. I would trade 10 mpg for that.

[944boy]

Fair enough, I did not specify! Maybe both? (I was going to post a picture but had trouble finding something safe for anyone anywhere to view).

But yes, 110lbs. Not sure which one costs more in upkeep though...

[Perfectlap]

110 is good as long as she at least 5-7 and blonde.