Rabbit 2.5l - squeezing out the best MPG

[theholycow]

I'm experimenting with ways to increase my fuel economy. I'm getting pretty decent mileage, but I'm trying for better. I've adjusted my driving speed and acceleration rate as slow as I'm willing to do, which is the most important part. I've removed my antenna (which was mainly for another reason) and increased my tire pressure, both of which theoretically can help slightly.

Mainly, my experiments involve shift points and throttle. So far, shifting extremely early and keeping the revs very low make a big difference.

My driving is 40% freeway, 60% backroads/town/rural highways. I measure my MPG by dividing miles on the tripometer by gallons on the pump. The 2 door Rabbit does not have the MFD, so I can't get the car to report it to me.

On my very first tank, I shifted in the 1800-2200 rpm range. Including a few hours spent learning the clutch (new MT driver), I got 27mpg.

Then, for a few tanks, I experimented with higher shift points - 2500-3000rpm, 2200-2800, etc...and got between 25.9 and 26.4mpg.

I returned to shifting low, and tried to go even lower. I also sprinkled in some fun by doing lots of passing on two-lane roads requiring lots of downshifting and revving way up, as well as a few hard acceleration days when I was late for work. I got 28.06mpg.

For my latest tank, I tested out a theory I read on the standardshift.com forums. The theory is that you should floor it (wide open throttle (WOT)) and use different shift points to moderate your acceleration rate rather than using different throttle levels. As long as your shifting low you won't accelerate fast, won't create much power, and won't use much gas -- but in the meantime, having the throttle open wastes less energy trying to suck air in through a tiny opening. I am skeptical, not for the usual cited reason that flooring the pedal always means making more power and using more gas; I know that if the engine is not revving fast, it's not going to suck in much air and therefore won't use much gas. No, I am skeptical for two reasons -- one being that the computer behaves differently for WOT than part-throttle (open loop, richer mixture, pre-set fuel tables, etc) and the other being that VW's DBW system might not even go WOT just because I floor the pedal.

Skepticism aside, I did get my best mileage so far: 28.13mpg. However, I didn't do quite as much fast/fun driving as I did in the previous 28mpg tank, so I'm guessing that it's no better and maybe slightly worse than moderate throttle combined with very low shift points. It certainly didn't produce the result I feared, where my economy would dive to <20mpg. It was kinda fun getting through 5 gears in a few seconds time, and the gas pedal makes a strangely satisfying plastic "thud" as it hits the floor.

Questions? Comments? Suggestions?

[BlaineWasHere]

Interesting study.

[RJS5689]

Ive heard that theory. But if you think about it, do you realize how much stress you put on your engine? Going WOT in a high gear at low RPMs, yea thats quite a strain.

[theholycow]

A lot of people mention the stress thing, but I'm not sure why it would be particularly stressful. If you're not making a lot of power either way, what part of the engine is getting stressed?

If it was getting a lot of air and fuel, then yes, it would create a lot of power and stress; but at low RPMs, it does not pull much air and therefore does not use much fuel.

So anyway, there is another thing I'm doing which I forgot to mention. I'm not using neutral while coasting; at first, I would put it in neutral as soon as I saw a red light, but now I leave it in gear until I have to declutch. This lets the wheels turn the engine, allowing it to use DCFO (Deceleration Fuel CutOff) mode instead of spending gas on idling wile the car coasts in neutral.

[Sloth!]

definitely interesting

[WakeHead]

I won't be participating in this study with my R32.

[nate122]

uhm well.....

the best i got was 25 mpg and that was when iwas breaking in the engine.
on my phone i downloaded this free program that you put the amount of gallons inputed and the miles driven and it calculates it for you.
my average right now is 23 mpg which isn't to bad.
i never used the ac in my car at 2800 miles :)

even thought gas prices have been high.. i still stomp on it once in awhile.

i have a auto and i always use tip cuz the drive mode SUX!

it shifts when im going uphill.. literally on 5th gear at 1800 rpm going up a hill with no power.....

[RJS5689]

Originally Posted by nate122

uhm well.....

the best i got was 25 mpg and that was when iwas breaking in the engine.
on my phone i downloaded this free program that you put the amount of gallons inputed and the miles driven and it calculates it for you.
my average right now is 23 mpg which isn't to bad.
i never used the ac in my car at 2800 miles :)

even thought gas prices have been high.. i still stomp on it once in awhile.

i have a auto and i always use tip cuz the drive mode SUX!

it shifts when im going uphill.. literally on 5th gear at 1800 rpm going up a hill with no power.....

The average on my Stage 2 GTI is also 23+MPG though. It really shows how inefficient VWs 5 cylinder really is.

[theholycow]

Originally Posted by RJS5689

The average on my Stage 2 GTI is also 23+MPG though. It really shows how inefficient VWs 5 cylinder really is.

Well, the whole point of using a smaller engine + a turbo is that it's more efficient than a larger engine when you're not using lots of power.

Still, the only time my 5 cylinder got less than 26mpg was when I accidentally left it idling for four hours. Don't forget that nate122 has a traditional automatic, not a DSG or MT.

FWIW, the US EPA compares cars scientifically using proper methods to make sure all variables are equal, and the 2008 2.5 gets one more MPG than the 2008 2.0t in city, and is the same for highway. 22/29 vs. 21/29. Those numbers are for their new 2008 more realistic estimates where they accelerate harder, drive faster, use the air conditioner more, and test based on colder outside temperatures...resulting in lower numbers than previous.

nate122, is your Rabbit a 2008? EPA's estimates show an improvement of 3mpg city and 1mpg highway for the 2008 model over the 2007 for the MT, but I didn't check the auto.

[dieselraver]

jesus, really??

i really must have a lead foot, i was filling up every 230-250 miles per fillup (before the gas light went on) but pretty damn close to E, on average that means that i was getting only 15-20mpg

[Sloth!]

Originally Posted by nate122

on my phone i downloaded this free program that you put the amount of gallons inputed and the miles driven and it calculates it for you.

you mean a calculator?

[NoVA_GTI]

Wow, my GTI /w APR 93 Oct easily gets 31 hwy / 27 cty if I drive it right.

[Sinan]

Originally Posted by Sloth!

you mean a calculator?

hahaha!

[fairladyz_gt-r]

My GTI get 30+ also if i follow the speed limit

[BlueWabbit]

nice read up totally something to wonder and think about good work but so far on my 08 CW 5spd rabbit it has about 1500k and im averaging about 22.4mpg im guessing the car needs to still be broken into and the car needs to get used to my habit but even in my 07 i shifted around 3k top only would have to shift at 4k if i really needed too and i still didnt get horrible gas mileage but i've done a trip about an hour and 30 mins away from town i got about 25.7mpg? i believe crusing between 65-70 mph.

holy have you tried pumping the middle grade gas? because even in my 07 i did regular but i've been wondering if i ran a good 5 tanks full on the middle grade maybe since the car is running a bit richer will i get better mileage? interesting.

edit:: my 07 and 08 are both manuals btw so i understand your concept.

[theholycow]

Hmm....I wonder what variables could account for the difference in the observed economy I've gotten vs. what you've gotten. Of course, the first and most obvious thought is difference in driving style, but I'm not so sure.

I've only got 4000 km on mine now. When I wrote "my first tank", I didn't just mean the first tank where I tried to keep track; that was the very first time I put gas in my brand new car. Therefore, the issue of breaking in the engine doesn't explain it.

Your '07 would definitely be less efficient, they changed the intake and the chip (and maybe some other things) between '07 and '08, for efficiency and power. The EPA economy estimates went up along with the HP. Still, I would expect you to get ~24mpg shifting under 3k, if you drive the same combination of city/highway as I do.

For your 90 minute trip, did you only make and return from that trip, and calculate your mileage based on that; or did you use a whole tank as normal, which happened to include that trip? That trip would take 1/3 of your tank at an average of 25.7mpg, so if you used a whole tank before calculating, the trip itself could have been over 30mpg.

I haven't tried using gas of different octane ratings. I'm pretty sure that at 9.5:1, our engine can't do anything special with higher octane, even with computer-controlled spark timing. I hope someone more knowledgable can confirm that or explain how I'm wrong.

I'm going to guess that in your '08 you haven't tried low shift points, and that you generally drive much more congested city driving. My commute, as I said above, is "40% freeway, 60% backroads/town/rural highways". Maybe I should define it better to make comparison easier; it could make a rather large difference. My whole commute is on low-traffic roads, and there are some long rural stretches without stops. There's lots of level roads, and I have only one uphill launch -- and it's barely uphill at all.

So, looking at a map of my 38 mile commute, here's approximately what I have:
17 red lights / stop signs
0 to 5 stops behind left-turning cars
14 mi 20-60 mph (country roads)
16.5 mi 70-85 mph (this is the freeway portion)
7.3 mi 40-60 mph
1 mi 20 mph (my neighborhood and the long driveway at work)

Looking at it that way, I've only got 17 to 23 stops in over 22 miles of non-freeway driving. That's probably not a lot of stopping.

[BlueWabbit]

the 80 min trip (calculated from one trip there, a total of 2 hrs and roughly 40 mins round trip) i just passed on what i got on my average with my 08 2dr there is the MFD now so i just read off the average i got for that trip since on the MFD there could be two functions the 1st one is the average you got on the whole trip im assuming it resets after the car been sitting for a while the 2nd one will be another average im assuming since you got the car from day 1.

well my driving is probably 50 in town / city and 50 free way there isn't much rural areas around Cali but i believe the 08 had more than just intake / chipping like you said i believe they did some internals as well to get that extra 20 horses.

agreed with the different octane ratings as well i was talking with my dad about this for maybe a good hour but with higher octane it wouldnt much such a significant difference only besides getting chipped that would like you said change the whole ecu.

your commute does look simple if that is your daily drive to work but i do believe i have some uphills part in my commute. now is your 38 mile commute a around trip to work and back home? because i have quite a similar commute as well from home to school to work.

but no i have no tried the low shifting points with the 08 so far im just driving my normal style of shifting under / around 3k rpm after it starts to gather up some miles i'll start the low shifting points. for some reason i still believe that the first couple of tanks of gas will be gone fairly quickly due to the car still being new and need to be broken in but just my thought.

i'll try to figure out my commute..

red lights and stop signs: roughly 15 to school thats about 16 miles (including freeway) from school to work would be... 5 another 15 miles (including freeway) or so
i'm not quite sure on how much i do of which but i could maybe ball park the average mph i am doing maybe about 50-70 because of the freeway driving

17 to 23 possible stop in a stretch of 22 miles? that is not a bad commute at all oh also i gotta include traffic jams as well not sure if idiling for couple of mins would take into account and usually in jams i dont go super fast i just leave it in 1st and let her coast.

[Kool_aiD]

Originally Posted by nate122

on my phone i downloaded this free program that you put the amount of gallons inputed and the miles driven and it calculates it for you.

miles2go?? i tested that... if not then its a similar program lol... but yah those are kinda cool

i heard once before that you can actually save more gas by starting from 2nd gear than first gear... just easing the clutch a little more... maybe try that? anyone else hear that

[Drone]

Interesting! What type of fuel are you using, and is it the same type and brand for each tank of gas?

[theholycow]

Originally Posted by BlueWabbit

i just passed on what i got on my average with my 08 2dr there is the MFD

How did you get the MFD on the '08 2dr Rabbit? Was it part of an option package? Mine was the base model and does not have the full MFD.

(Note: If you're reading this, I forgot to insert the photo. Damnit.) (Edit: Oops, sure enough, I forgot. Well, I'm still waiting to download it from my home computer, I don't remember which one it is so I have to download a few hundred megs to look for it before I can post it. I'll post it later.)

Anyway, the MFD is reportedly not at all accurate, but I wouldn't know.

is your 38 mile commute a around trip to work and back home?

Nope, that's 38 miles each way. It takes 45 to 50 minutes.

but no i have no tried the low shifting points with the 08 so far im just driving my normal style of shifting under / around 3k rpm after it starts to gather up some miles i'll start the low shifting points.

Hmm...I consistently got 26mpg shifting between 2500 and 3000, but again, it sounds like your route is less efficient than mine.

i'm not quite sure on how much i do of which but i could maybe ball park the average mph i am doing maybe about 50-70 because of the freeway driving

Average MPH is 99.999% of the time way lower than the driver's guess. The way you described your commute, I doubt that it's physically possible to average 70 or even 50. How many miles is it, and how many minutes does it take from the time you drive away to the time you arrive at your destination?

oh also i gotta include traffic jams as well not sure if idiling for couple of mins would take into account and usually in jams i dont go super fast i just leave it in 1st and let her coast.

Traffic jams eat up quite a lot of gas, that would definitely account for a big difference between your MPG and mine. I have had a total of two freeway-stopping traffic events (which cleared in, at most, a couple miles) since I started my job last November.

Originally Posted by Kool_aiD

i heard once before that you can actually save more gas by starting from 2nd gear than first gear... just easing the clutch a little more... maybe try that? anyone else hear that

I've done some 2nd gear starts, and I suspect it could save a slight amount of gas by not idling the engine during the time you're shifting.

Originally Posted by Drone

Interesting! What type of fuel are you using, and is it the same type and brand for each tank of gas?

I'm using 87 from WalMart, Cumberland Farms, and Shell. I choose based on price and convenience.

[theholycow]

Okay, as promised, my '08 2 door base model Rabbit's Fewer Function Display...

[BlueWabbit]

no idea how i got the MFD but i just do haha on my 07 4dr though it did not have the MFD so i dont know what is the case there but if you say it is not accurate well damn all this info i've been saying could be false xP (well the average mpg anyways)

yeah your route seems less of a headache i'll try making my shift at 2500 today see if it helps out any instead of 3000 since it seems like to be big PITA in 1st and 2nd gear eating up the gas.

uhh miles to school is about 17 takes about 15 mins on a good day. miles to work from school is about another 16ish? i believe another 15 or 20 mins. but they are mostly freeway so i just tossed out 50-70 mph average.

i remember my photography teacher in high school said if you are in a traffic jam turn off your engine and you save a little gas but i am a bit skeptical because it probably requires more gas just to start up the engine than leaving it idle.

i dont think buying/using a cheap to a well known gas will affect the car in any way correct? since i know shell and chevron use those cleaning crap or whatever to promote their gas but it wouldnt matter since there is a standard that all gas stations must follow by correct? i remember when i first got my 07 i only gased up in shell since i was skeptical about using cheaper gas like from not well known gas stations.