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Factory new cars and poor gas mileage

Is there truth to the tale that brand new cars get only the minimum MPG for the first 3 months or so until the car gets “broken in”?

Not in my opinion. Cars will be broken in within the first 25 miles, or less.

It improves slightly but nothing really significant.

Actually with all things it depends on the vehicle. Some cars, such as VW’s with the 5 cylinder engine, seem to improve with age in the mileage department. Almost all oil analysis I’ve seen with a new car would suggest they all undergo a period of break-in during the first 10K miles. Toyota’s seem to be very low, where many other brands are much higher. A well broken-in engine with looser tolerance will certainly offer slightly more power and efficiency than a new motor. Of course when people hear (and are told) by manufacturers the days of break-in are over they are referring to the need to drive the car in a certain manner when new, such as not exceeding 4K rpm, vary rpm’s often, etc.

So in summary, yes cars do break in over time, but not in the way they did 30 years ago, it’s more subtle. And yes mileage will improve in some cars though usually it’s only 1-2 mpg.

Mine have always improved slightly after the first few thousand miles, typically maxing out at about 5,000 to 10,000 miles. Perhaps it takes me that long to get the proper “feel” of the individual car.

Call it a myth. Any increase in mpg after a week or two is purely minimal, and may be simply the result of the driver adapting to his new car.

I’ve heard this, but never really seen it. After the first tank of gas (who knows how they filled it at the dealer) it’s always been pretty much the same. I do have one odd counter-example. I bought a brand new 1989 Nissan Maxima. It consistently gave me 25 to 26 MPG on highway trips driving from Virginia to Pennsylvania. I kept a fuel log in the car for every tank and mile. Somewhere around 90,000 to 95,000 miles it started getting 29 to 30 MPG on the same highway trips to PA. It kept it up over a couple of years and didn’t go back down. I never figured that out, but surely the engine was broken in long before 90K miles.


I’ll take a wild stab at your Maxima experience. After about 90,000 miles it is possible to see enough carbon build up in the combustion chamber that your engine compression raises ever so slightly. This in combination with ever loosening tolerances allowed you to peak on a so-called mpg curve. Best explanation I can come up with if everything else is equal.

My new Toyota Corolla achieved top mileage after only 3000 miles. Some cars may take a little longer.

The “break-in” period is for the benefit of properly seating the piston rings, to prevent later oil burning. A brand-new engine may be a little “tight” and need to wear a bit to reduce friction, but I would expect very little improvement in mileage from just that. I would agree with the other posters that much of the improvement comes from the driver getting attuned to the car and its behavioral quirks, such as when the best shift points are.

Just buy a Porsche. They claim there is no required break-in period, so you’ll get proper mileage from the get-go.

I had the same experience with my wife’s 2006 Sienna, the mpg did improve after 2 or 3000 miles but only by 1 or 2 mpg.

Ed B.

Your gas mileage will improve to about what is right in about 3,000 miles. The whole car is tightly wound when new and will break in. The car won’t get “minimum” gas mileage right out of the box but it won’t get its best right away.

A lot of us get our best gas mileage when the car is brand new because we are driving extra gently during the break in.