Strange but I take it...

[pfr]

I had an oilchange done at the dealer's at my usual 7,500 mile mark (got at $79 coupon in the mail). There is always a catch and I let them change the belts as well (93 kmiles and consider it insurance).

The funny thing is that I am getting more than 2 miles/gallon improvement on my mileage. I usually get 27.x on highway trips and this weekend's trip showed 30 mpg for 150 miles. I haven't change my driving style (if you'd want to call it that; up to 80 whenever reasonable), tires are the same, etc.

Anybody would venture a theory?
Thanks - Peter

[brettbimmer]

Small gains but: clean oil so less internal resistance in your engine. Also, did they add air pressure to your tires? How about outside temperature? A few ideas that may give you a slight increase in mileage.

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[Oli77]

That kind of deviation in my MPG usually comes from weather. The colder, the worse it gets.

[Lanister]

I thought it's the other way around. The colder the air the more efficient the combustion is. My car shows noticeable pep when the ambient temperatures drop.

[Oli77]

I don't notice much of a change in butt dyno with temperature changes but the drop in gas mileage is very noticeable.

[Smolck]

I thought it's the other way around. The colder the air the more efficient the combustion is. My car shows noticeable pep when the ambient temperatures drop.

More pep because cold air is more dense and the DME adds fuel to compensate. But that would also use more fuel. Personally I don't see a change in mileage on cold vs warm.

[stephenkirsh]

I thought it's the other way around. The colder the air the more efficient the combustion is. My car shows noticeable pep when the ambient temperatures drop.

It is, but when it's cold in winter, there's more stress on the car. People run the heater, headlights, defrosters, lower pressure in the tires until the warm up, etc.

So cold air alone is better, but most often really cold air means there's more things going on with the car.

[pfr]

Soo...
The oil has been changed in regular, appr. 7,500 miles intervals and the mileage had been pretty stable around 27.x mpg over the past two years, summer or winter. I have now snowtires on, so rolling resistance would be worse if any difference would want to show up. I am baffled and while I do appreciate your thoughts, so far nothing convincing...
- P

[stephenkirsh]

How many of the 7500 miles were on the snow tires?

[gmurphy]

Reset your MPG to see if it goes back to what it was. Mine changes all the time depending on the weather and how I drive :)


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[pfr]

How many of the 7500 miles were on the snow tires?
about 3,400


Reset your MPG to see if it goes back to what it was. Mine changes all the time depending on the weather and how I drive :)
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Yeah, mine too. I do reset it time to time, and since it happened I reset it several time to make sure it was consistent.

[elsanto]

Check your air pressure.. I have a mechanic who LOVES to over inflate my tires. Especially if you have non factory sizes on, and they go by the doorjamb sticker.

[pfr]

Check your air pressure.. I have a mechanic who LOVES to over inflate my tires. Especially if you have non factory sizes on, and they go by the doorjamb sticker.

This probably could start a brand new discussion: I keep my tires 2 psi over the pressure recommended by the sticker. I learned in my otherwise wasted youth that this will improve handling and mileage...???

[Oli77]

This probably could start a brand new discussion: I keep my tires 2 psi over the pressure recommended by the sticker. I learned in my otherwise wasted youth that this will improve handling and mileage...???

Yep its here. (http://www.zhpmafia.com/forums/showthread.php?1579-What-is-the-recommended-tire-air-pressure-for-the-E46-BMW-330-ZHP&highlight=inflation)

[stephenkirsh]

Does anybody ever accidentally flash their brights when cycling through the display modes on the OBC? I feel bad when I do that lol

[gmurphy]

Does anybody ever accidentally flash their brights when cycling through the display modes on the OBC? I feel bad when I do that lol

Sometimes lol.


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[tkundhi]

Few thoughts. Did engine oil weight change? Are your snow tires narrower? Mine typically are. What about road conditions on your recent trip? Surface and elevation. Where these different that your typical usage. And are you comparing apples to apples. Is you 27.x just highway or mixed driving?

t.

[stephenkirsh]

Does anybody ever accidentally flash their brights when cycling through the display modes on the OBC? I feel bad when I do that lol

OMG I posted this in the wrong thread. Sorry guys. :(

[pfr]

Few thoughts. Did engine oil weight change? Are your snow tires narrower? Mine typically are. What about road conditions on your recent trip? Surface and elevation. Where these different that your typical usage. And are you comparing apples to apples. Is you 27.x just highway or mixed driving?

t.

The oil weight (and brand) is the only thing I know changed: my Indie is using some European oil with 0-40 and the dealer of course uses "BMW" 5-30.
My snow tires are 215/50/17 square; however they have been on for a long time now, so no change there. The trips I am talking about are basically the same trips, on the same roads, highway (mostly I95) with a little local section at both ends, but I noticed a difference in local driving too.

- Peter

As far as I can see this is apples to apples, except for the oil but can that account for 10% improvement? Especially as it went to heavier?