Gas mileage increase after break-in?

Has anyone documented a gas mileage increase from 0 miles to whatever you consider broken in on a new car/truck? Not asking for butt-dyno guestimates, actual calculated miles/gallons over the break-in period. I never have been able to confirm an increase maybe because I didn't have repeatable driving conditions. My dad drove 50k highway miles a year when he was working and kept meticulous records, new car every 2 years, and saw at best something in the low tenths, this with mostly GM cars up to 1990. StevieC, you drive a bunch, what have you seen?
 
Messages
8
Location
FL
2003 Focus wagon, MT, Zetec, increased about 10% over the first 10k miles. Logged every gas stop, now at 190k. No significant mechanical problems yet. I'll never forget when I logged a mileage drop of around 2 mpg in town - unexplained for about 5 mins, then I saw the ethanol postings on the pumps!! I'm the only person who drives the car.
 

gathermewool

Site Donor
Messages
8,932
Location
New England
I keep records, but none of them are meticulous. I would guess that the vast majority of folks here who actually do keep records do so similar to how I do it...meaning our data is nearly worthless.
 
Messages
3,195
Location
Western S.C.
I bought my Mazda (below) in December, and was initially disappointed in its fuel mileage. By May, it was doing about 25% better, between combined effects of warmer weather and break-in. It stayed about the same the rest of its long career. Tires are one of the biggest factors in break-in mileage improvement.
 
Messages
17,578
Location
...
I saw the mpg go up after a few thousand miles. It was a subtle trend but if you keep records or have a app then it is noticeable. Mine started out the first thousand around 28.xx then it has stabilized around the 4500 or so market at 31.5 for mixed driving. This is a Mazda CX-5
 

RW1

Messages
249
Location
JBLM, WA
I use an auto maintenance app that tracks my MPG. My Tundra with the 5.7L engine was averaging 14 mpg during the winter and 15 mpg during the summer. That is, until I hit 50K miles. It started to increase from there and now I'm averaging 17-19 mpg year round.
 
Messages
857
Location
Maryland
I've had a bunch of new cars over the decades. It takes me about a month or so of daily driving to truly learn the feel and handling of a brand new vehicle. In every car I can recall, after the first month or two (about 1500-2000 miles), fuel economy stabilized and stayed consistent for the life of the vehicle. There are always predictable variations due to seasonal changes. Variations also happen if your normal daily commute changes for some reason. Another possible consideration... With modern cars, the "computer" learns your driving habits and controls the transmission shift points to accommodate your particular style. Disconnect your battery for 10 minutes and your transmission has to re-learn how your drive. My 2018 Mazda 3 had a 300 mile break-in procedure which recommended no cruise control, RPM not to exceed 4k and mix of city/highway driving. With all that in mind, I don't think a vehicle stands a chance of getting consistent fuel mileage until after after the first 4 fill-ups. Ray
 

AZjeff

Thread starter
Messages
5,362
Location
northern Az where the Antelope play
50k break-in? Did you change tires or something else significant? Good stuff. Was wondering with so much of today's engine functions computer controlled and tighter manufacturing if there would be much change.
 

gathermewool

Site Donor
Messages
8,932
Location
New England
Originally Posted by RW1
I use an auto maintenance app that tracks my MPG. My Tundra with the 5.7L engine was averaging 14 mpg during the winter and 15 mpg during the summer. That is, until I hit 50K miles. It started to increase from there and now I'm averaging 17-19 mpg year round.
A 24% increase in mileage from breaking-in is impossible to believe.
 
Messages
180
Location
Ponchatoula, La.
IMHO, mostly placebo and computer learning. It's in the way you drive, tire pressures, and seasons. Have never seen a measurable increase in MPG during and after "break-in" that could be repeated tank after tank.
 
Top