First, let’s stress that the owner’s manual for your car is the authoritative guide to any break-in procedures. Almost all manufacturers have recommendations in these handbooks. That being said, engine break-in is subject to opinion, just as are oil change intervals and tire pressures.
Breaking in a new car used to require following a stringent driving style for a certain number of miles. Many of the newest engines, though, have no break-in at all. As we stated, all the info you need is in your owner’s manual. Because policies and procedures for breaking in a new car are changing with rapidly advancing engineering and technology, this is an interesting topic among car experts.
Click and Clack, the Tappet Brothers, AKA Tom and Ray Magliozzi on the popular National Public Radio show, Car Talk, say the issue is properly “seating the piston rings.”
Tom: What does that mean? Well, at the heart of the engine are your pistons. They look like soup cans, and they go up and down inside the cylinders. It's crucial that there is a perfect, tight fit between the outside of the pistons and the inside of the cylinder walls.
Ray: So, the pistons are surrounded by spring-loaded rings, which push out against the walls and keep the seal tight. Otherwise, oil will get past the rings, and you'll "burn oil."
Tom: And the theory of "break in" is this: If the rings and the cylinder walls don't come out of the factory matching up perfectly, the break-in period gives them a chance to conform to each other during relatively "light duty" service, which involves going slowly and varying the speed.
Ray: Why is it 1,200 miles on one car, and 600 on another? Because it's not an exact science. I think each manufacturer is making its best guess as to how much time the rings will need. It's probably based on how many people have whined to them in the past about their cars burning oil. They look at their warranty claims and say, "OK, guys, let's jack it up another 200 miles and see if that helps."
Tom: It's interesting to note that some carmakers are so confident in their precision manufacturing that they require no break-in period at all.
Here’s the typical break-in advice published by one major car manufacturer:
“A long break-in period is not required for the engine in your vehicle.
“Drive moderately during the first 300 mi (500 km). After the initial 60 mi (100 km), speeds up to 50 or 55 mph (80 or 90 km/h) are desirable.
“While cruising, brief full-throttle acceleration, within the limits of local traffic laws, contributes to a good break-in. Wide-open throttle acceleration in low gear can be detrimental and should be avoided.”
Pretty “middle-of-the-road,” isn’t it? That’s because engine break-in isn’t the big deal it once was. To get a bit technical, that’s because engine manufacturers are able to hone the cylinders with far greater precision. Where cylinder clearances used to be in the thousandths of an inch, now they are in the ten thousandths. Bores are rounder and straighter. That means the pistons and the rings fit better, and that means there is less need for “wearing-in” the parts. There’s less friction, less heat buildup and less chance of improper seating of the piston rings.
Most experts agree that the “golden rule” in breaking in your new car is to warm up the engine before running it hard. That doesn’t mean idling for any length of time – not necessary! It does mean “taking it easy” the first few miles until you see the needle on the temperature gauge moving into the “normal” zone.
The process of engine break-in starts with low revs and about one-quarter throttle. Gradually, you rev a little higher and add a little more throttle. During this period, don’t keep the engine revs high for a long time. The idea is to gradually use more and more of the rev range, allowing the engine parts to wear-harden over time. The break-in for today’s engines is generally 700 to 1,000 miles.
One thing that hasn’t changed with engine break-in is the need for an early oil change. While the recommended oil change intervals for modern cars and trucks have been extended, the break-in oil and filter change should occur around 1,000 miles. This will clean out any fine metal particles dislodged in the first miles you put on your new car. Once those are out of the engine, you should be good to go, and go and go.