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Jerome View Drop Down
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  Quote Jerome Quote  Post ReplyReply Direct Link To This Post Topic: gas mileage
    Posted: 05-Feb-2007 at 14:12
Sooo-for the last 2 weeks here in iowa I'd say the average temp has been about 5 degrees. This has awoken a myriad of strange noises (fans squeaking, belts being cold, other normal below-freezing sounds). I attempt to give my car about 5-10 minutes of warm up time before I head to work, but sometimes this just doesn't happen.

The biggest hit I've seen so far from the cold is the gas mileage. Most of the miles I drive are around town (a town with wayyyy too many stop signs and lights). Anyway, I just figured it up and I'm getting about 11.5 mpg. In the summer it's between 15 and 16. I've been putting in 91/93 octane since December.

So I'm wondering your guy's opinions. In this cold weather, what's the better gas to put in, or rather, which is probably the least wasteful? 89 octane burns more easily than higher octanes and that's what I was putting in during the summer since Premium was entirely too expensive.

I don't think there's anything wrong with my car, but I'm going to hook it up and scan for codes when I can stand being outside for longer than 5 minutes.

I hate winter.
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SirRangeALot View Drop Down
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  Quote SirRangeALot Quote  Post ReplyReply Direct Link To This Post Posted: 05-Feb-2007 at 15:51
Yah, my mileage sucks too. On one of the trips I took last fall I got over 450 miles on one tank of gas. In the winter I'm lucky if I get 200 miles on one tank. VERY frustrating. But I still love my W8. =)
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  Quote pistik Quote  Post ReplyReply Direct Link To This Post Posted: 05-Feb-2007 at 18:31
Winter sucks....eh...
I just a minute ago came from gas station where I put 79L of 91octane in my W8. And since last full fillup I did 485km. That is 16.2L/100km (14.6mpg). Well that is 75%city and 25%HWY in Toronto and whole week it was -10degrees celsius....freezing like hell.
But interesting thing is that my trip computer #2 showed me average consumption of 15.2L/100km (15.6mpg) over last 485km. I do reset my #2 trip computer every time I fill-up. And for whatever reason it happened few times I spotted diferences between computer and reality. sometimes just like -0.2L/100km(I guess normal) and other time like -1L/100km.
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Jerome View Drop Down
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  Quote Jerome Quote  Post ReplyReply Direct Link To This Post Posted: 05-Feb-2007 at 23:14
I noticed that same exact thing. Like you, I reset the #2 computer every time I fill and it's always off by about 1 mpg. Probably due to the amount of gas used on engine startup. Oh well, there are very few things I'd trade my car for...I kinda just throw all of this into my entertainment budget
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  Quote pistik Quote  Post ReplyReply Direct Link To This Post Posted: 06-Feb-2007 at 00:59
There is a way to do adaptation of fuel consumption computer by setting the value from 85 to 115% as correction. I just found it in Bentley manual. When I have little more time I will try to readapt my fuel consumption meter.
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  Quote B5crazy Quote  Post ReplyReply Direct Link To This Post Posted: 06-Feb-2007 at 08:52
I have also been surprised to see how my mileage go down this winter. My guess it's about 3 mpg. My '99 1.8T on the other hand didn't loose much at all in the winter.

IMHO, part of the problem is that the W8 takes longer to warm up compared to a 1.8T so it will not be running at peak efficiency.
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Jerome View Drop Down
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  Quote Jerome Quote  Post ReplyReply Direct Link To This Post Posted: 06-Feb-2007 at 12:21
Originally posted by pistik

There is a way to do adaptation of fuel consumption computer by setting the value from 85 to 115% as correction. I just found it in Bentley manual. When I have little more time I will try to readapt my fuel consumption meter.


Yeah, let us know how you make this adjustment.

OT: I tried to do a full scan last night and VAG-COM said I needed to register
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  Quote fitzski Quote  Post ReplyReply Direct Link To This Post Posted: 06-Feb-2007 at 12:33
My mileage is remarkably consistent. My lifetime is 18.2 mpUSg, with my lowest ever being 16.6 and my best being 20.8. I don't notice a drop off in the winter at all (and its been pretty cold here for the last few weeks... -37C w/windchill yesterday).

The FSI/MFI trip computer is known to be sporadic in its accuracy. If you keep good records and pay close attention (i.e. by using the #2 trip meter), you can make the correction that pistik mentions to account for the percentage difference that you notice. For example, if your calculated mileage is consistently 5% less than what the trip computer says, you can make the correction with a VAG-COM (in the Instruments module, IIRC), by changing the default value (100) to 95.

Edited by fitzski - 06-Feb-2007 at 18:34
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  Quote pistik Quote  Post ReplyReply Direct Link To This Post Posted: 06-Feb-2007 at 15:39
I think those with manual transmission have little agvantage when it comet to gas mileage. In reality automatic transmission introduces quite bit of power loss which esentially will show in poorer gas mileage.
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  Quote Garfield Quote  Post ReplyReply Direct Link To This Post Posted: 06-Feb-2007 at 16:22
Everything I have read says the Auto is more economical than the manual - one of those rare occasions I guess.

You should be running 98+ octane, less is for emergency use and will reduce your power (the ECU detects things like 'knock' and detonation and adjusts the timing accordingly to protect the engine). Less power means the engin has to work harder, the W8 is not a lightweight.

It is the same principle that the 1.8T is more economical than the normaly aspirated 1.8

Sorry guys I don't have mine till the weekend but I have never run my BMW on anything but 98+ octane and it DOES make a difference of up to 40 miles on a tank in the BMW, you shouldn't be pouring cheap and nasty stuff into a W8. The higher octane fuels will burn cleaner too and contain specialist 'cleaners' to prevent carbon build up and soot generation etc, meaning your whole fuel system and engine end up cleaner internally and more efficient as a result.

Best way to prove it is by trying it yourself but do it using your head not the cars electronics which are a guide only, fuel dispensing pumps are calibrated regularly.

Run as close to empty as you dare then brim the tank with a grade of fuel, note the mileage, then the next time you fill simply brim the tank with the same fuel grade subtract your last mileage from the current mileage and divide by the gallons you put in the tank this will give you an MPG figure, do this as often as you like but stick to the same grade of fuel - this gives you a great opportunity to confirm or reject what the onboard computer is telling you.

Before switching to the other grade of fuel run to near empty again and repeat the filling and mileage calculations as often as you like just as before making sure the fuel grade you use is consistent.

You can't simply do different grades without a 'consistent' period in between because the car doesn't 'instantly' adapt, it can take up to 250 miles so three fills of half a tank or more should ensure it has adjusted. Having multiple samples gives you a better idea and helps eliminate those oddities like the 6 hours you spent trying to get out of NY on Friday night, it will also help you to see if temperature really is an issue (humidity definately is - cars like it cool and humid), all kinds of other things like altitude are a factor too.

You can use this info to 're-calibrate' the onboard computer reading.

Providing your driving has been reasonably consistent you should have an idea which fuel works best obviously the more samples you take the more accurate your assesment will be.

But lets face it when you bought a W8 was good gas mileage a criteria ... bad choice if it was ... [IMG]smileys/smiley2.gif" align="middle" />

Edited by Garfield - 07-Feb-2007 at 01:41
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