One of the most frequently asked questions on the forums I visit is, “Do I need to do anything special to break-in an engine?”

Responses tend to follow the conventional wisdom, as stated in most owner’s manuals: for the first 500-1000 miles, avoid strong acceleration and steady speeds.

Another school of thought says that with the much tighter tolerances and more precise assemly of todays low-emission engines, no break-in is necessary.

Yet another approach advises warming the new engine up then accelerating at full throttle. Supposedly, this creates a better seal between the piston rings and the cylinder wall, by forcing the rings against the wall around their entire circumference.

I’ve never seen any recent laboratory results that support the first approach. I’ve heard powertrain engineers espouse the second. And the site linked for the third displays pistons from engines broken-in the first way vs. the third.

What I’d like to see: a controlled test of the three approaches. Take three groups fo engines, one for each approach. Drive them 1,000 miles as prescribed. Then dyno and emissions test them, to see how powerful and clean they are. And maybe take them apart to look for signs of poorly sealed rings. Any consistent differences? 

So what to do now, since no one has published the results of such a test? I’d like to say to follow one approach, if only because it’s “better to be safe than sorry,” but the first and third approaches contradict one another. So which one is the safe approach?

The third approach actually makes the most sense to me, but as the author grants it’s scary for people used to the traditional approach.

I can say this: I’ve been conducting TrueDelta’s reliability research for a few years now, and no one has ever reported a repair necessitated by an improper break-in procedure.