Q: I was very interested in your comments on "engine break-ins." I would not be quite so quick to dismiss break-in as obsolete.
I am a nerdy retired engineer and keep data on the maintenance and operation of the cars I own. In September 2007 I purchased a new 2008 Acura TSX with the 2.4-liter four-cylinder engine. I was interested in whether or not I could observe any break-in behavior. It took approximately 12 months and 17,000 miles to fully break-in the car. When I plotted miles per day vs. miles per gallon, I got a mathematical curve that seemed to make sense. As miles per day increased, so did mpg, a not totally unexpected result. The relationship was not linear but looked more like logarithms. I threw out the first 16,000 miles of data so that the curve represents only the values for the broken-in engine. Then I went back and calculated an expected value of mpg for every fill-up, then checked the actual mpg for that fill-up and plotted this ratio for every fill-up vs. time.
This plot is still somewhat noisy, but overall it starts around 0.9 (the actual mpg was nine-tenths of the expected) and rises steadily over the first year to a value of 1.0 (the mpg equals the expected value). The average of the curve has varied not more than 2 percent since then.
A: The toughest part of answering was to edit down the original question to a manageable/publishable size — and still keep the information understandable and accurate. I sincerely hope I've done so.
The data and conclusion are extremely interesting — thank you, Ron. You appear to have mathematically confirmed that miles-per-gallon improvement is due to the cumulative effect of all drivetrain components getting "comfortable" with each other — not just the engine. Engine, transmission, differential, hubs, bearings and all rotating, reciprocating and geared components will "wear-in" during thousands of miles of normal driving — not during a relatively short initial driving cycle specifically designed for "break-in" — then stay "happy" for tens of thousands of miles.
Years ago during a rebuild on one of my race engines, I failed to adequately hone one of the cylinder walls before installing new piston rings. When the engine was first started, the rings did not "seat" properly, allowing excess oil past the rings, quickly fouling the spark plug in that cylinder. I disassembled the engine after a total of three minutes of operation and was quite surprised to find that wear on the new rod bearings appeared identical to wear on the bearings I had replaced after six hours of operation.
As your data confirms, the concept of "break-in" isn't obsolete — it occurs during the first several thousands of miles of normal driving. Today's vehicles and engines just don't require a specific driving cycle or break-in period to deliver full service life.
Q: Last summer I bought a 2009 Kia Spectra with 59,000 miles on it. Am I safe in assuming that all the regular manufacturer's recommended 50,000-mile maintenance has already been performed or is my vehicle due for its 50,000-mile check-up? I have kept up with the oil changes.
A: Unless the service invoices/maintenance records are in the glove box or you can confirm the maintenance was performed through a VIN number check with a Kia dealer, you should assume the manufacturer-recommended maintenance has not been done.
Your Kia's maintenance schedule calls for replacing the air filter every 30K miles, cabin filter every 10K miles and engine oil and filter every 7,500 miles. The remaining scheduled maintenance in the 45-50K mile range is a series of inspections, many of which you could do yourself, and tire rotation.