Bad MPG during new car break-in period - Fuelly Forums

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Old 03-25-2012, 01:33 AM   #1
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Bad MPG during new car break-in period

Don't be discouraged by bad MPG on a brand new car. Keep driving it, be patient, and prepare to be surprised.

I've been keeping track of my new 2012 Subaru Forester since I bought it new with 11 miles on the odometer. My normal driving habits around Raleigh consist of a pretty good mix of city & highway miles, and I would have expected an average of somewhere over 20MPG. But it was pretty frustrating to have this car hovering around 16-17MPG all the time.

But then I went on a road trip to Philadelphia.

I fueled up in Raleigh and drove until somewhere in Maryland before fueling up again. My in-car MPG display estimated I was in the 29-30MPG ballpark until I hit Richmond, VA which is where I-95 gets dicey. Bad traffic patterns persist through northern Virginia, into D.C., and Baltimore. This brought the overall average down, but still... 27MPG overall for the trip. Not too shabby (for this car)!

You'll see a huge dip in the chart. That represents my time in Philadelphia where you're just going from traffic light to traffic light, slamming on the brakes for dumb jaywalking pedestrians, etc.

MPG shot up again, but not as sharply, for the next fillup. I had rain (often heavy) following me my whole return trip from Philadelphia to Raleigh. While the Subaru was very happy in the rain, it didn't help my MPG. Nor did the pockets of slow scared motorists who don't respect the notion of sticking to the right side. 45MPH in the passing lane in a posted 70MPH zone? Seriously??? ;-)

It's funny, how the MPG suddenly shot up after being down in the teens for awhile. The salesman did mention these cars take 1 or 2 thousand miles to train the engine computer before the MPG settles in where it needs to be, and that seems to be reflected in my fuelly chart. I wanted to point this out to anyone else who might be discouraged by the MPG they are seeing with their new car.

I think this car can probably deliver 30MPG if I do my part. I'm not the most gentle MPG-minded driver.

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Old 03-26-2012, 11:23 PM   #2
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I heard this statement too about after break-in the mpgs will increase. It is very hard to get any true results from one car because of the many, many variables that affect any one car's mpg. You may be able to see results if you drove the same trip repeatedly but then your odometer has clicked off more miles than the break-in.

The only way to know for sure is to analyze a large number of cars that are the same make and model where fill up data is available since new. Fuelly has that data available as long as the car is a popular car on on here with lots of data from day one.

In my case I bought (now sold) a new 2010 Jetta TDI. On the VW forums it is frequently said that after a good 10k mile break in the mpgs will increase and even more so after 20k miles. So I called their bluff and plotted the mpgs of something like 50 or 60 new Jetta TDIs from initial dealership miles when purchased to 20k+ miles. Guess what? No real difference from 0 miles to 20k+ miles. The graphed mpgs for each car and the graphed mpgs for all cars averaged together was a level line that did not increase over time. There was some city/hwy wiggles on each car's mpg graph but the overall line from first data point to last data point was flat and did not creep upward.

I wish I had saved that spreadsheet but when I sold that car I deleted it's folder on my computer and that spreadsheet was in that folder.

One may possibly see a very, very slight bump from 0-500 miles but based on my research it is negligible. Let us know if you do a similar comparison with the Subaru Foresters. BTW, I think that is a good car choice. If I weren't a VW diesel fan that would be one of the cars I'd consider. Good luck! I think the 30 mpg goal is doable consistently if you do your part and don't go any faster than 70mph on the highway.

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Old 04-06-2012, 10:14 PM   #3
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I bought a new 2011 Kia Soul with the 1.6 liter engine and 5-speed manual just over a year ago. I discovered Fuelly about two months later, so I've been tracking mileage here since 5/2011. The car had about 200 miles on the clock when purchased (due to a transfer form another dealer) and around 2200 when I started tracking it here. Overall average MPG has been 26, which is right on the EPA city estimate. We use it almost exclusively as a "city" car, so I am happy with the results. I didn't start tracking mileage here right away, but I was paying attention to mileage before that. The overall average hasn't changed in 1 year and 9k miles. I have read on a number of Kia forums about how break in improves mileage, but I haven't seen that with the Soul.

I just bought a new 2012 Mazda5 6-speed and will be filling it up the first time today. It will be interesting to see if it experiences any break in improvement as time goes by. It started with 8 miles on the clock.
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Old 04-10-2012, 09:30 AM   #4
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I had two Honda Civics from new, put 270K on the 01 and 148K on the 08. Neither one changed much for gas mileage, but I do drive them easy for the first couple tanks. I think the break in mileage increase is an anachronism that has exaggerated effects with newer engines. Hopefully my 2012 CRV will prove me wrong though, got 33mpg first tank. I do know thatthe first oil change will be different oil, less moly. The dealer says the mileage should go up after that but the civic didn't.
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Old 04-10-2012, 10:27 PM   #5
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The theory of break in mileage versus regular mileage comes from high performance engines with high compression ratios and exceedingly tight ring tolerances that come from the factory. I've noticed it in turbocharged diesel engines on boats, it takes most engines with tight compression rings at least 25-100 hours to seat the rings into the cylinders. During that break in period there is an elevated friction loss due to the rings grinding (seating) against the cylinder walls as they wear into each other.

I would guess that this phenomena is able to be documented in engines like a TDI and probably the Chevy Cruze Eco turbo but harder to see in engines built with looser tolerances like a Kia Soul, Honda Civic, etc.

That being said, it is usually on the order of less than 10% mileage change from break in to long term operations consumption under similar conditions. On a yacht for example where the new engines consumed 15 gallons per hour per side at a given cruise rpm (speed varies on a boat due to currents, winds, and other conditions that vary from one day to the next so we use gph not mpg)may decrease to something on the order of 13.5-14 gph. It isn't like your new TDI is going to jump from 30 mpg to 50, but if you're banging around 36 an increase to 40 is probably reasonable everything else being equal.

Just my $0.02 from years of driving boats and building engines for cars, boats, airplanes, and motorcycles.
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Old 04-11-2012, 11:07 PM   #6
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I have a 2012 Kia Soul which gets in a 50/50 mix just under 24 mpg. I have 3200 miles on the car. I have noticed a 1 mpg improvement in the last 2000 miles, but this is well under the stickers 29 combined mpg. My dealer did a mileage test and they got 24.4 mpg and Kia says it is within specs. Kia also said my mileage would improve 'gradually'. When I asked them to put their specs and what kind of improvement I would get in writing they refused on both counts.
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Old 04-12-2012, 12:07 AM   #7
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How many miles is your average journey (each direction)?
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Old 04-12-2012, 08:13 PM   #8
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My mother's new Mazda got 21mpg on its first fill up, 24city/33hwy. For 300 km on the odometer i think its fair to be a couple mpg off when most of the driving is in the city.


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