# Better Gas Mileage...



## oempls (Aug 9, 2004)

My wife's 2006 Rabbit seems to be getting worse and worse fuel efficiency the last few months. I have done the required 20k and 40k service on the car as it is only at 51,xxx miles but it doesn't seem to help much. Aside from some VW Goal wheels and Toyo tires, the car is stock. Any suggestions? I feel that the engine cover and filter is one of the worst designs ever but without any proof of beneficial gains to mpg and hp it's hard to convince her to go with a CAI or intake.


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## Brianjk (Apr 15, 2002)

What's "worse and worse" mileage?

I manage 32-33mpg on average. BSH intake, 5-40 or 0-40 synthetic. Driving style and A/C use have a significant impact.


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## tchilds (Nov 21, 2008)

Manual offers a whole chapter on driving green. Vw is a fun to drive economy car with flat torque curve. It is not an ultra economical transporter with zero fun and questionable safety (weight, brakes, etc).


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## oempls (Aug 9, 2004)

Her mileage ranges from 23-28mpg combined. It's primarily 50+ mph and she rarely uses her AC.


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## le0n (Jun 12, 2013)

i lost ~5-6mpg when switching to 18" aftermarket wheels with 225 width toyos. it was instantaneous, hah hah. the setup is heavier than the steelies and the engine feels it. however, if you've always had these wheels on there and you noticed the change in mpg just recently, then it is probably not the culprit.

no need to put a cai on her vehicle; mpg results would be negligible. make sure the tire pressures are where they need to be.

on average, how many miles to the tank does she get? if it's around 375 or so, it's probably ok. if it's around 280 miles to a tank, you have to start looking at all the variables because something probably needs attention, because you shouldn't be getting poor mpgs with majority highway driving.


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## oempls (Aug 9, 2004)

She is just running 17" VW Goal wheels with regular sized tires. I know her tire pressure is usually always good since she is paranoid of getting another blowout. As for mileager per tank, she claims 280-310 on average which I know is low.


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## thygreyt (Jun 7, 2009)

people focus too much on outside factors when thinking on fuel economy.

In reality: fuel is combusted on the engine, so focus on your engine in order to improve your fuel efficiency.
What oil do you use? any additives? service? did you replaced the spark plugs when needed? 

make sure that your engine is running top notch, and then the rest is easy.

top 2 reasons for fuel efficiency: airflow and lubrication.


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## le0n (Jun 12, 2013)

^^ according to the OP, he has done the 40k mile service, so it doesn't hurt to focus on the outside factors; because making the realizations and checks costs nothing. So when those 'things' are not questionable, then you can proceed with a little more knowledge going in.

Now aside for the car being due for an oil change (11k miles since 40k miles), everything else should be tip top, hence the reason to start this thread.

Give us a little more info, oempls. You can inspect your plugs to see if your're possibly running rich. If so, you can clean the maf and throttle body (because the system will be open) to see if the performance improves.

If you're dropping below 260 per tank your O2 sensor may need to be checked via vagcom.


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## hop2it (Jul 6, 2010)

I'll throw this in, some people's tankfuls are filling once they get to 3/8 or a quarter of a tank, just being sure your going down to "E".


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## oempls (Aug 9, 2004)

le0n said:


> Give us a little more info, oempls. You can inspect your plugs to see if your're possibly running rich. If so, you can clean the maf and throttle body (because the system will be open) to see if the performance improves.
> 
> If you're dropping below 260 per tank your O2 sensor may need to be checked via vagcom.


I have been thinking about changing out the plugs even though they looked fine. What do you think about changing out the coilpacks as well? What plugs/gap do you use? I have VCDS, how would I go about checking the O2 sensor?



hop2it said:


> I'll throw this in, some people's tankfuls are filling once they get to 3/8 or a quarter of a tank, just being sure your going down to "E".


What do you mean running it down to E?


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## Dronks (Jun 7, 2011)

thygreyt said:


> people focus too much on outside factors when thinking on fuel economy.


That's because a heavy foot or bad braking habits will sway MPG a lot more than some older spark plugs and conventional or unapproved oil.

My average is around 27 MPG with about 75% highway, but that's at 75+ MPH so it's not so much better than city mileage.....I need the 5-speed from a diesel :laugh:


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## tchilds (Nov 21, 2008)

What octane are you running? I only run premium 93 from shell or BP and worst mileage I can get is around 360 a tank. Im at 600 ft elevation.


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## oempls (Aug 9, 2004)

We went on a trial of 3 tank fulls of premium and regular grade. The differences was maybe 8-12 extra miles on a tank of gas. She uses regular grade Chevron or Shell. As for the oil, our dealer sends us coupons for synthetic oil changes regularly so it's just the dealer Castrol Synthetic.


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## le0n (Jun 12, 2013)

Here's a part of some logging I was doing to see how much timing is pulled when using 87 octane fuel. In a few days, I'll be able to grab the log for the 93 octane (which is what I normally run).

These two charts are aligned on the X axis (time) values.









You can compare any of those values to your readings.

Sorry for the large image (not phone friendly), but it's a lot of small info.


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## oempls (Aug 9, 2004)

We only have 91 octane here in Cali. I see the differences but on paper, we didn't see them at the pump.

Ordered new coilpacks and plugs today. See if that helps at all. I am still concerned about that restrive airbox. I can't imagine a filter on top of the engine bay being very effective. With a intake I would imagine it would be helpful.


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## le0n (Jun 12, 2013)

oempls said:


> We only have 91 octane here in Cali. I see the differences but on paper, we didn't see them at the pump.


i posted the charts in regards to the question below.



oempls said:


> I have VCDS, how would I go about checking the O2 sensor?


i don't have vcds, however, you can probably just as easily monitor/log any of those O2 sensor values for comparison.

it appears that from a cold start and at idle, the bank1 sensor2 rocks along at about .45 volts, then jumps up to around .70 volts after the down-shift leaning effect. the bank1 sensor equivalency will try to stay at 1.0.

i guess one key thing is to make sure your sensor values are fluctuating and not remaining stagnant at any point.

edit:

here's the highway file


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## oempls (Aug 9, 2004)

Thanks. I am going to try out the plugs and coilpacks along with an oil change to see what happens.


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## Brianjk (Apr 15, 2002)

Have you tried any fuel system/injector cleaner?

I do remember getting a nice bump in mpg after using some. I cant remember if it was 3m or chevron/techron brand, but it definitely made a difference.


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## oempls (Aug 9, 2004)

No, haven't done that yet. Might as well give that a shot as well.


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## oempls (Aug 9, 2004)

Any suggestions on removing the coil pack wiring harness? Seems like a really tight fit compared to the 1.8T and 2.0T


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## oempls (Aug 9, 2004)

Upgraded to the red top coil packs and new plugs. Car already feels better. Gonna give it the fuel treatment at the next fill up.


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## BlixaBargeld (May 5, 2008)

MAF gone bad? Reads too much air = too rich of a mixture


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## oempls (Aug 9, 2004)

Not sure right now. I did a scan on the engine with no findings. Her car seems to be driving alot better now after the plug and coilpack change. Gonna measure the findings on the next tank.


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## zukiphile (Oct 28, 2000)

tchilds said:


> What octane are you running? I only run premium 93 from shell or BP and worst mileage I can get is around 360 a tank. Im at 600 ft elevation.


A tank is not a standard unit of measurement.


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## le0n (Jun 12, 2013)

zukiphile said:


> A tank is not a standard unit of measurement.


no, but it's an understood unit of measurement here; roughly equivalent to 12.5-13.5 gallons.


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## Brianjk (Apr 15, 2002)

The easiest way to tell gas mileage is to reset the trip counter when filling the tank all the way up. Then divide the mileage by number of gallons at the next tank. Do this for a few tanks in a row, and it's a pretty good average of your mpg. I do this every tank, but I realize some people do not like to fill the tank all the way up..


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## zukiphile (Oct 28, 2000)

le0n said:


> no, but it's an understood unit of measurement here; roughly equivalent to 12.5-13.5 gallons.


It's lazy.

It isn't as if anyone buys gasoline measured in tanks. Everyone here buys his gasoline in gallons or liters. It is very simple arithmetic to report a useful figure.


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## le0n (Jun 12, 2013)

i purchase my fuel by the "tank" by swiping my card and waiting for the pump to click. just because it is sold by the gallon here, doesn't mean i drive up thinking to myself; "you know what? i think i'm going to purchase 13.4 gallons of fuel today. that should be enough to fill my tank."

besides, everyone here knows how to calculate his/her mileage. but it's probably not a practice that is done every time they fill up. that would be silly. yes, the arithmetic is simple, but not necessary.

what is common practice, lazy or not, is when someone presses the trip reset after fueling to see how far they can travel, or how many days they can travel to work and back on one tank. if their driving style hasn't changed since the last time they've done so, the results should be somewhere in the vicinity as the last reported miles per tank.

my gas warning light came on at 380 miles before arriving at the office today. i know i can easily go to 410 miles before needing to fuel up, but that would put me in unfriendly territories looking for fuel because my house is 40 miles away from here. so, i'll get a tank of gas on this side of town.

also, if someone questioned how many miles i got to this tank of gas, the answer would be 380 miles.


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## oempls (Aug 9, 2004)

le0n said:


> i purchase my fuel by the "tank" by swiping my card and waiting for the pump to click. just because it is sold by the gallon here, doesn't mean i drive up thinking to myself; "you know what? i think i'm going to purchase 13.4 gallons of fuel today. that should be enough to fill my tank."
> 
> besides, everyone here knows how to calculate his/her mileage. but it's probably not a practice that is done every time they fill up. that would be silly. yes, the arithmetic is simple, but not necessary.
> 
> ...


Agreed.


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## zukiphile (Oct 28, 2000)

le0n said:


> i purchase my fuel by the "tank" by swiping my card and waiting for the pump to click. just because it is sold by the gallon here, doesn't mean i drive up thinking to myself; "you know what? i think i'm going to purchase 13.4 gallons of fuel today. that should be enough to fill my tank."


The quantity of gasoline is always denominated in gallons or liters, just as the price will be in dollars, not whatever-it-takes-to-fill-the-tank, and the distance is measured in miles or kms rather than how-ever-far-I-got-before-I-stopped-at-a-gas-station.



le0n said:


> my gas warning light came on at 380 miles before arriving at the office today. i know i can easily go to 410 miles before needing to fuel up, but that would put me in unfriendly territories looking for fuel because my house is 40 miles away from here. so, i'll get a tank of gas on this side of town.
> 
> also, if someone questioned how many miles i got to this tank of gas, the answer would be 380 miles.


That first paragraph is why the second doesn't involve any standardized measure.


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## le0n (Jun 12, 2013)

zukiphile said:


> That first paragraph is why the second doesn't involve any standardized measure.


i've already agreed that is wasn't a standard unit of measurement, so i'm not exactly sure at what you're trying to get out of this...



le0n said:


> on average, how many miles *per 12.5-13.5 gallons* does she get? if it's around 375 or so, it's probably ok. if it's around 280 miles *per 12.5-13.5 gallons*, you have to start looking at all the variables because something probably needs attention, because you shouldn't be getting poor mpgs with majority highway driving.





oempls said:


> As for mileage *per 12.5-13.5 gallons*, she claims 280-310 on average which I know is low.





le0n said:


> If you're dropping below 260 *per 12.5-13.5 gallons* your O2 sensor may need to be checked via vagcom.





tchilds said:


> I only run premium 93 from shell or BP and worst mileage I can get is around 360 *per 12.5-13.5 gallons*. Im at 600 ft elevation.


^^ fixed?



le0n said:


> also, if someone questioned my mpgs for this tank of gas, the answer would be *28.14-30.40 mpg*.


using standardized measurements just clears things right up 
(keep in mind that i'm guessing on the amount of fuel (in gallons) it would take to fill up my tank because i've yet to make it to the gas station)


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## oempls (Aug 9, 2004)

Way to nuke it :facepalm:bro.


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## le0n (Jun 12, 2013)

i was kind of close:


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## 08 VduB WaBBiT (Apr 3, 2008)

Would being Catless improve the MPG's?


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## wushugs (Oct 1, 2008)

thats not too bad? i drive 90% highway. and i get rarely get above 29mpg.. hover around 70mph.. sometimes above slightly.. almost never above 75-80


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