i've had my 2009 auto fit sport for 2 years. i've driven about 23,000 miles in mixed highway/suburban driving.

overall miles per gallon....
year 1: 31.6 mpg.
year 2: 32.1 mpg.


summer months average about 2.2 mpg more than winter.

.....................year 1.............year 2
dec/jan/feb: 30.5 mpg.........30.2 mpg
june/jul/aug: 32.5 mpg.........32.4 mpg

if you compare the first 4 months i had the car vs. those same months a year later.....

nov/dec/jan/feb2009: 30.7 mpg
nov/dec/jan/feb2010: 30.6 mpg

 

Its not a myth. Actually happens after break-in is properly done, by numerous manufacturer's tests. However, if break-in done imporopoerly, such as wide open throttlke breakin there will be a loss in hp as well as mpg.Your 3% gain is typical.

 

I did a lot of WOT when I first got my GE8. No loss in power or MPG here. Babying your car during the break-in process is a myth.

 

I've had my 09 for over 2 years, but it's hard to tell any difference in mpg, esp since it returned excellent mpg when new. I was surprised though on a recent 375 mile trip to yield 43.6 mpg one way. It included just some city, sections of gusty headwinds, some A/C, doing mostly 73 mph and one gigantic mountain. Tire pressure was 32-33 psi.

375 miles from 1 tank and exactly 2.0 gallons remained. Theoretically, with the same 43.6 mpg mileage, cruising range is at least 457.6 miles!

 

i made about 40 MPG going home for the first time (over 100 miles) with the fit and after 1 year... i still make 40~MPG doing exact same trip with 16k miles on the car

 

Here's my overall for the 1st year. As my engine broke in, It got colder so if my economy improved due to break-in I really couldn't tell because of the drop in Temp. I'll have to compare this winter against last winter. Overall however, my average is 38+ for the life of the car. I can't complain.

https://www.fitfreak.net/forums/2nd-...ear-38mpg.html


~SB

 

Babying a car for break-in is not proper brake-in. Some WOT is required but the main requirement is to not run at constant rpm for very long. Occasionally the engine should be reved to redline so cylinder wear is evened over the whole useable rpm range. And yes, do not load engines hard before fully warmed up but also do not 'lug' the engine either at any time. Most engine builders use computer programs to break-in new rebuilt engines now days.
And to see 3% takes a dyno run. Actually 6 to get proper statistical data.

 

Its not break in parse, carbon builds up and raises compression and if no knock you will get better mpg because higher compression makes the engine more efficient. Also btu's in gasoline affect gas mileage, which is different every time they drop gas even at same station.

 

DO NOT believe this. Anyone with an engineering background or knowledge of metallurgy will tell you to follow the makers instructions exactly. Metals working together have to have a period of break in to mesh correctly. This is not babying. This is paying attention to what several dozens of engineers working together with years of experience in their fields plus decades of data from the maker have come up with. Do it. Do not think that you have more knowledge of this automobile than these people, I don't care how recently you got your GED.

To the OP: Yes, you will get better gas mileage after break in because of less fiction due to proper matching of metals. Probably around 3%.

If you are using Ethanol "enhanced" gasoline you will get around 7% LESS mileage than if you used gasoline without Ethanol. This little fact was not mentioned when our all-knowing government mandated the use of this junk. The mileage decline will be about .7% for every 1% of Ethanol used, up to about 50% at which point the decline stops.

For more info on this see:

Ethanol Fact and Fiction
Washington’s Foolish Fuel Policy - Energy Source - How we power the world - Forbes

 

There was a article awhile back, where a guy that works for a race team did a experiment with two brand new engine.

On one, he floored it almost the whole time

the second one he babyed it.

After they took the engine apart, he showed us the piston from both engine. And the one he floored it had less debrease or carbon or whatever. I'm not a mechanic or anything but even i can tell it looked to be in better condition than the one he babyed. He said something about the piston ring , but i barely remember. i'll try and find the video/article again.

 

If you get enough carbon buildup to raise your compression ratio by even a tenth switch your gasoline suppliers. Good gasoline has virtually no carbon build up in 50,000 miles.

 

Babying the engine means not reving over 2000 rpm and even accepted lugging the engine in order to have the least rpm. And that will indeed load up the carbon deposits.

 

The additives in gas is to control deposits, but there are other factors that cause carbon. Incomplete combustion is the main cause. Premium gas has less high carbon hydrocarbons like c9-c15, plus a good premium has friction modifiers that lubricates the upper parts of the motor. BMW has 2 tests 50000 and lifetime. I agree that a good gas will prevent deposits but every batch and condition of driving changes. BMW also requires premium in all there cars and I wonder why? They have the same knock sensors, o2 sensors and the only difference is the fuel air might be set for max horsepower at full throttle instead of MBT.

 

That would be true, because carbon wont build up on a engine that is floored once in a while.Carbon is very corrosive and retain heat which causes other problems. The main reason you want to control carbon is the fuel absorbs in the carbon and the engine runs lean, more fuel is added and the compression raises and more knock happens and incomplete combustion making the problems worse. You use more gasoline and more gasoline goes into the crankcase diluting the oil to name a few.

 

True, but so vague as to be useless. What is "once in a while"? What is "floored"?

This from Automotive Tech Tips:
Automotive Tech Tips

"The best way to clean carbon build-up out of your engine is NOT to take the car out and run it as hard as you can. This only results in meetings with local law enforcement personnel, and doesn't do much for cleaning out carbon. "

Carbon will not build up on engines using modern name-brand gasoline. Cars that are driven short distances and not warmed up to operating temperatures are subject to small amounts of carbon buildup. Cars with high mileage will develop carbon buildup due to oil blow by around the rings. Cars that are operating with a too rich mixture can develop carbon buildup. Other than that, there should be no
problem.

This is an easy one. So does Mercedes. Has nothing to do with carbon buildup. They want you to do that because their engines develop about 6% more horsepower using Premium. If you are not street racing and are just driving normally, use regular. Save your money. There is way too much differential between regular and premium prices.

Where did THAT definition of "babying the engine" come from? Babying the engine just means not running up to red line while cold. Not using red line shifts every time you leave a stoplight. Following the builders recommendation for a proper break in. If you have an AT, the operating program will not let you lug the engine to damaging levels. If you have a MT and use too high a gear then you get bucking. That is lugging. If you don't throw the clutch then it will stall. This is not good for the engine (or drivetrain either) but it has nothing to do with carbon buildup.

 

I thought some cars require premium because of knocking issue. Since the engine is high compression, it requires premium.

 

YES.. to a certain extent. It's all related.

Higher compression engines produce more HP than one with lower compression (everything else remaining the same). Most higher compression engines require premium in order to detonate the gas at the most optimum time to produce the most HP. Using a lower octane fuel in one designed to run on premium, requires the engine to retard the timing a little, meaning that the gas is not being detonated at the optimum time, so MAX power is not realized.

All things the same between regular & Premium(save for octane level), Premium has no more explosive power than regular. It just allows an engine designed for premium to utilize it's own capabilities to the fullest extent. Compression ratio has alot to do with it but not everything. a lot of it is total engine design. The FIT has as High of a compression ratio as some of the "High Compression" engines of just 10 years ago (b18C series) yet it doesn't require Premium. It's because of changes in engine design.

~SB

 

That's a big debate too in forums of all kinds.

 

Myth - If properly maintained you will not see an increase nor decrease in mpg.

 

Realistically, you'd have to measure your economy during the initial few months against the same few months the following year (given that you had the same driving practices both years. You'll also want to make sure that the ambient temperatures are the same (average) for that period of time. (wunderground.com is a good historical data reference). If i can get to it, I'll look at my numbers & temps as I'm about 15 month into ownership. Someone who who buys a car in November/December that lives in the northern states and drives about 1000 miles/month, will likely see an increase in economy at about the 5k mark... Because it's getting warmer out and economy increases as spring/summer approaches. Depending on A/C usage, someone might see the exact opposite if the AC is always on in the summer but the temps are in the 60's or 70's in the winter. (southern states).

Break-in as our Fathers and Grandfathers knew it is very different. I highly doubt we'll see the increases in our engines that they saw in theirs. Primarily because of tolerences etc... Todays engines are just that much better, more refined, and likely need less "break-in" time. It's like oil... and progress... Welcome to the world of "this aint' yo daddy's car".

Engines will likely always need to be "broken in" and during this period, I think some improvements are to be expected, but I personally don't expect to see the large differences that we saw 10, 20, let alone 30+ years ago (which is likely the stigma most people are going by.) Larger changes are likely not due to break-in but other factors such as warmer weather, driving style changes, % of ethanol in the fuel, etc...

~SB