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Old 01-12-2011, 05:08 AM   #1
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What's the most efficient RPM for Mazda3 hatchback?

I have a new 2010 Mazda 3 sport hatchback with manual transmission (2000 miles on it). I like the car a lot, but am rather disappointed in the fuel economy... averaging about 26 mpg, with probably 70/30 city/highway driving.

This is the first manual transmission I've owned, and I'm wondering what the most efficient engine RPM is for this car. I've been trying to keep it absolutely as low as possible, so I'm often in 5th or 6th gear and ~1000 rpm around town, when not accelerating. Is this inefficient? Should I be in a lower gear and a slightly higher engine speed?
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Old 01-12-2011, 03:50 PM   #2
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you are at a slight disadvantage MPG wise at present for 3 reasons:

1) you only have 2000 miles on the clock, the engine will still be tight

2) as you say you are doing 70% city driving - cruising gives the best economy

3) MPG will always be lower in the winter, I lost at least 5 mpg in winter (the engine takes longer to warm up, and therefore runs richer for longer)

I would be looking for revs of 1500 - 2000 as you are bordering on labouring at 1000rpm, at 30mph I would look to be in 4th, not higher.

Trev
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Old 01-13-2011, 12:09 AM   #3
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Thanks, Trev! I didn't know that brand-new engines got lower fuel efficiency. What's the explanation for that?

I will try and keep the engine at slightly higher speeds as you suggested, and I do think I have been noticing some effect of temperatures in the 30s, although it rarely gets below freezing here in the Portland, OR area.
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Old 01-13-2011, 12:27 AM   #4
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They take several thousand miles to get broken in. Our 2009 Scion delivered average mileage in the mid-20s for the first 5,000 miles of ownership or so, but has averaged close to 30mpg for the next 40,000.

The 1000-1500rpm range is fine when you're not accelerating. It is not an efficient range at large throttle applications, though. Most modern DOHC passenger car engines become most efficient under WOT at 2500-3000rpm. Note that since you don't need WOT very often, it's advantageous to stay below that at part throttle.

You will see a much bigger difference from driving conservatively (accelerating slowly and coasting to stops) than you will from driving at different RPM, as long as you're staying below 3000 or so. Remember to coast in gear rather than in neutral.

The winter gas also makes a noticeable difference. A few threads down there is a discussion of seasonal gas blends. I notice anywhere from 2 to 4mpg difference when the winter gas starts. This also makes it a bit harder to compare the effect of temperature.
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Old 01-13-2011, 02:27 AM   #5
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I have no problem gauging the effects of temperature.

My car has instant mpg in it's display, there's a noticeable difference when the car is warm (you don't get the full benefit until not only the engine but the transmission has warmed up)

I agree with your conservative driving tips, but would add one - if you got cruise use it !
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Old 01-13-2011, 08:23 AM   #6
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Good point. None of my cars have a mileage meter in the dash. If your Mazda has one, they can be a good comparison tool to judge your driving by, even if they sometimes aren't very accurate.
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Old 01-14-2011, 09:41 AM   #7
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I'd try to keep the rpm's between 1500-2000. Most new cars have deceleration fuel cut off and cuts off the injectors while coasting if the rpm's are above 1100-1200 range.

Also as others have stated new engines are not broke in good and run tighter than an eingine with 10K+ miles. I'm not sure what mileage they consider broke in now, but back in the 60's and 70's they said allow 5-10K miles for the break in period.

Others have also mentioned winter blend gas and cold weather being factors. I usually lose a few mpg's during the winter and this year has really hit me hard, because I moved to a part of the country that has colder temperatures during the winter.
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Old 01-16-2011, 07:32 AM   #8
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Here is a good article talking about specific fuel consumption in passenger cars:

http://autospeed.com.au/cms/title_Br...6/article.html
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Old 02-09-2011, 02:26 AM   #9
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Definitely need to up the rpms. At 1k it is lugging. Bad.
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Old 02-13-2011, 09:58 PM   #10
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I would be careful with the on-dash fuel mileage calculator. I owned a 2006 chevrolet cobalt, and according to the dash calculator, I was getting 34-38 mpg, but if I did the math myself, it was usually about 6 mpg lower than the dash said.
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