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The first thousand or so miles in my 2017 smart fortwo BRABUS cabriolet, I only averaged between 23 and 32 mpg's. I realized it's because I couldn't stop racing in it.


I got most of that out of my system and now I drive the way I'm legally supposed to, so I have managed to get upwards of 45 mpg's rather easily as long as I'm willing to allow most traffic pass me because I'm "only" traveling at the speed limit. The key is to avoid aggressive acceleration too, avoiding turbo spooling when unnecessary.



So the engine advancements of the 453 compared to the 451 is night and day, as the 453 is the superior engine design... and that's not a dig at the older 451, which I still drive as well. :)
 

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How many miles on the odometer?? The 451 models took until around 30,000 miles to get great mileage. Synthetic oil only makes it worse until the motor wears in. Synthetic oil doesn't allow them to wear in, some have switched to regular oil for 10K-20K miles to get things seated properly.
The majority of engine break-in only takes the first few revolutions the engine makes, and with the proper procedure of running to higher RPMs and allowing engine braking to slow the car down, is virtually completed within the first 100 miles, regardless of which oil is in the engine.

Many high end manufacturers such as Ferrari, Mercedes, and even Chevy in the Corvette, deliver the car with synthetic oils as the factory fill. If this weren't acceptable to break in an engine, then they wouldn't do this.
 

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Well going by personal experience, the first 30K miles I averaged 38 MPG, after that it slowly increased to 42-48 MPG That was with recommended oil changes and easy driving. Not the only smart I heard that with
 

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Well going by personal experience, the first 30K miles I averaged 38 MPG, after that it slowly increased to 42-48 MPG That was with recommended oil changes and easy driving. Not the only smart I heard that with
That's a very common experience among new car owners. I believe there are many factors, but the actual engine break-in isn't one of them.

But first, the engine break-in part. I own a Corvette and many owners say the engine doesn't break in for 20-30k miles. That was debunked pretty clearly years ago by someone who had opened up their engine with about 200 miles on it and did a microscopic examination of the cylinder bores, posting detailed and high resolution pictures, and then repeating the process about 10k miles in (unfortunately after a valve failure). There weren't any visible differences down to a resolution of a few microns. He tried to photo the same location in the same cylinder. Of course, there could have been other factors, such as a low spot in either the cylinder bore or the rings in that location, but the overall sheen of the cylinder bores looked the same as far as everyone could tell.

There's also articles like this recent one:

How to Break-In An Engine

which when talking about engine break-in and seating of rings, says:

With today’s rings, especially moly-faced versions, this can be achieved in a very short period of time and certainly within 20 to 30 miles of street driving. In WOT dyno testing, likely the rings are seated by the end of the first few runs.

As far as what causes fuel economy to go up over time, a lot of it is due to wear, especially in surfaces that mechanically mate under pressure like gears, and in seals. Also, as tires get worn, their rolling diameter decreases so the odometer becomes a bit optimistic, and tires get harder as well which decreases rolling resistance. Probably the main factor is that people either just stop enjoying the performance of their new car as much, or they get more used to driving it in a way that maximizes economy. After all, how many people do you know that complain about how the transmission in the 451 works, fighting it when they first get the car, but after a while they learn how to drive it more smoothly and efficiently? And I know from direct evidence that I don't drive my ED nor my Corvette nearly as hard as when they were new, and economy/efficiency have gone up in both cases.
 

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It's good to know you have all the answers as to how I drive my car and how my particular vehicle is wearing internally.

I drive my car on the same road, to and from work daily, every working day year round. As such, there is little variations in the external effects except weather and temps which is why I use an average MPG over the life of the car. for the first 165K miles, I regularly tracked MPG on each tank. and averaged 4 or 5 tanks to get a running average.

At around 35K miles I did replace tires on my smart with absolutely no change in MPG as I used the same size and brand that came with the car. At the time, that was the only brand available in the stock sizes. so rolling resistance wasn't a factor. (same rolling resistance spec on the new tires as the old ones)

I can't give you a microscopic evaluations of the individual components, I did not have the oil analyzed at each oil change, or do a complete teardown every year to inspect for wear on seals and gears. Come on! its a daily driver and no way near the cost of a Corvette or exotic vehicle. Just a general idea of what I have seen, Real World (as the thread title says.)

In the end, if we discount any sort of mechanical wear-in, the only answer is magic.

While you are analyzing all the data from the various experts who constantly contradict each other, I will be out for a cruise in my smart! Happy motoring!!
 

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I thought this was a discussion forum. It sounds like you don't want to discuss and would rather be sarcastic. Have it your way, but your response says way more about you than it does about me.
 

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My 2015 Pure has 21k and getting good mpg is no problem. Local local driving 34. Mixed local/city 38. Short highway 42-44 and long distance 49. The wife once got 52 on a trip. I have a Scanguage and live in hilly Pennsylvania.
 

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2013 Smart, 98,000 miles. Daily 100 RT commute. Two cross-country trips. Several regional (tri state) trips. Regular dealership maintenance. No issues. Runs like new. Love my Smart! This is my second Smart. Recently purchased a third, newer model for future retirement vehicle. Keeping miles low on third Smart. 2013 still my favorite.
 

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Oh, forgot. In my 2013, I get an average of 41 mpg. In summer using A/C, 39 mpg. My 2016 gets an average 38 mpg, 35 in summer. 2013 has 98,000 miles. 2016 has 28,000 miles. 2013 is primary vehicle. Love it the most.
 

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40-42 religiously... ...not by the MPG dealio in the info center. Take actual mileage from tripometer and devide by gallons..
 
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