Tell me about breaking in an engine.

[Misnomer]

I am nearly ready to buy my first new car in 14 years. I'm hoping to buy one next month, but I might have to wait if the dealership doesn't think that my current car (an '02 that I bought used in '04) is worth more than I owe on it. I am also hoping to take said new car to an open track event in late July, when -- optimistically -- it would be just 2.5 months old. Which leads me to wonder if I'm insane.

How many miles are generally recommended as the break-in period? Will it depend on the car? What could happen to the engine if I totally stressed it before it was fully broken in?

[SmartAleq]

I used to be a product marketing specialist for GM, and per the official word there is no need for a break in period because all engines are run at the factory. If it makes you feel better, keep it under 60 for the first 500 miles. Me, I could never wait that long!

[Lanzy]

Drive it like hell while it is still under warrenty.

[FatBaldGuy]

We just bought a new Camry, and the dealer told us to not drive at constant speed for extended periods during the first 1000 miles. Other than that, no special break-in was required. YMMV for different cars.

[Faruiza]

SmartAleq is right on. I always found it amusing that the new cars nowadays come pre-broken and have been for well on oh, around 15 years now, but the rule of thumb has always been 55 for the first 500 miles. In fact, it will even say so in the owner's manual!
Does anyone know if that's because there are other systems at work that didn't get the full treatment at the factory?

[Digital Stimulus]

Originally Posted by SmartAleq

...there is no need for a break in period because all engines are run at the factory. If it makes you feel better, keep it under 60 for the first 500 miles.

We just bought a new Hyundai Tuscon 3 months ago. This is exactly what we were told, FWIW.

[Scuba_Ben]

Use a rubber mallet.

[Euthanasiast]

There are a couple of schools of thought on this, and one of them is to drive the hell out of the car for the first 500 miles in order to to allow the rings to properly conform to the inner wall of the cylinder. Going her easy will not completely force the rings into the perfect shape of the inner cylinder walls, possibly leaving gaps (though incredibly small) that could result in a slight decrease in compression in time. Also, if you adopt this policy, you need to change your oil after the first 500 miles in order to flush the small pieces of ring broken off in your oil during the break in period (I would do this anyway, whether you break her in hard or soft).

Whether this is still a viable method is open for debate as most modern vehicles are built to incredible tolerances and are broken in at the factory.

[Winston Smith]

Back in '97, I bought a small Toyota pickup (1/4 ton 4x2 5-speed) and a week after I bought it, towed a u-haul trailer from Atlanta to Boston. No break-in period, two thousand pounds overweight, towing on a manual transmission, through the mountains then two straight days of highway driving.

You couldn't more thoroughly abuse a new vehicle. I put 24,000 miles on it and only changed the oil once, right before I returned it (it was leased).

I never had a problem with it, though I doubt it ever saw 100,000 miles.

[Richard Pearse]

Originally Posted by Euthanasiast

There are a couple of schools of thought on this, and one of them is to drive the hell out of the car for the first 500 miles in order to to allow the rings to properly conform to the inner wall of the cylinder.

You shouldn't need schools of thought, just read the manual. My Toyota manual recommended avoiding constant speeds for the first 1000 km, other than that, no break in was necessary.

[Misnomer]

Thanks, everyone!

Originally Posted by SmartAleq

there is no need for a break in period because all engines are run at the factory

Best words I've read in a long time.

If it makes you feel better, keep it under 60 for the first 500 miles. Me, I could never wait that long!

I can't imagine how in the world I would ever go 59mph or slower for that long in any car, let alone a new one!

Originally Posted by FatBaldGuy

the dealer told us to not drive at constant speed for extended periods during the first 1000 miles

Originally Posted by 1920s Style "Death Ray"

My Toyota manual recommended avoiding constant speeds for the first 1000 km

What, exactly, does "constant speed" mean? Am I not supposed to maintain the same speed while driving, at all, for the first 1000 miles? The stretch of road I drive to work every morning at pretty much 40mph should see me varying my speed regularly? By how much? And how often? Of course I will consult my own dealer/manual when the time comes, but "avoid constant speeds for 1000 miles" just sounds like something incredibly tricky to do.

Originally Posted by Euthanasiast

There are a couple of schools of thought on this, and one of them is to drive the hell out of the car for the first 500 miles in order to to allow the rings to properly conform to the inner wall of the cylinder.

At the risk of asking a stupid question (since I know nothing about engines), would that advice also apply to a rotary engine? The car at the top of my list right now (Mazda RX-8) has one.

[Euthanasiast]

Originally Posted by Misnomer

At the risk of asking a stupid question (since I know nothing about engines), would that advice also apply to a rotary engine? The car at the top of my list right now (Mazda RX-8) has one.

I couldn't say since the primary difference is that the crank shaft in a rotary engine is stationary and the engine components rotate around it (which is a large difference), but I assume that any engine that uses rings around pistons fitted within a cylinder wall would qualify. Assume in this case equals WAG.

[Rick]

Originally Posted by SmartAleq

I used to be a product marketing specialist for GM, and per the official word there is no need for a break in period because all engines are run at the factory. If it makes you feel better, keep it under 60 for the first 500 miles. Me, I could never wait that long!

Well since every car ever built was started and driven out of the factory, you can say that this has been the practice since Henry was building Model Ts.
With the advances in metallurgy and precision machining, break in is not as necessary as it was back in the day.
On the many new Volvos I have driven as company cars, the gas mileage picked up at between 8,000 -10,000 miles. The car also got noticeably faster. This tells me the car was then broken in.
However the authority on your new car is the car maker. Read your manual. If it lists a break in procedure, follow it. If it does not, I would not be redlining the engine at every shift for a thousand miles or so.

Misnomer constant speed refers to engine speed. You don't want to run the engine at the exact same RPM for extended periods of time during break in. The risk (I have been told) is that the rings will glaze and the engine will then burn oil. I have never seen this, but that's the story. bottom line is, it is possibly an old wife tale, but it doesn't cost anything to follow the recommendation.

[Misnomer]

Originally Posted by Rick

You don't want to run the engine at the exact same RPM for extended periods of time during break in.

No danger of that happening on the track, where I'm constantly either flooring it or braking hard. Yay!

[Philster]

We all tend to forget that some parts, like rubber hoses and belts, and some plastics, are better with a little age. Brakes sometimes fit that mold, too.

Break-in periods ensure that all these parts work fine. With thousands of fresh parts on a car, a period of unfamiliarity by the driver and the first 1-3 problems just looming (are they minor or major/dangerous problems?), a break-in period is wise. Think beyond the internal metals, the rings, the pistons, etc. They need virtually no break in. Manufacturing tolerances are incredibly tight nowadays.

Tires? Brakes? Belts? All of these are nicely served by a light break-in period. The driver is also served by the break in period.

Fresh brakes connected to fresh tires are going to feel and react differently than brakes and tires that have been used. Steering and braking are as integral to your safety as anything. I think you are best served by a car that sees these characteristics 'normalized'.

[engineer_comp_geek]

I've owned a couple of cars where the engine computer went through a "learning" period. The owner's manual specifically stated that they wanted you to vary the driving conditions as much as possible, not only while the car was new, but also any time after the battery was replaced. They didn't want you to do Misnomer's constant 40 mph drive to work while the computer was figuring things out.