running in new car engine

What’s the best method for running in a new car engine? The owners manual states to keep the revs low and avoid using full throttle. The dealer advised to keep below 4500rpm and avoid traveling at one speed in any one gear for prolonged periods. Other people recommend loading the engine at low revs and high throttle settings, other people advise against it.

What is the best, proven method for running in a new engine to obtain maximum reliability over the life of the engine? The engine is a new, 2 litre four cylinder fuel injected petrol type.

I’d like to hear from mechanical engineers, not hearsay or gleaned from magazines.

I would assume that the recommendation in the manual is based on information from the engineering department of the manufacturer.

With today’s numerical controlled machines tolerances are held very close so clearances in things like pistons and bearings are very near optimum and a break-in really isn’t all that necessary. Most manufacturers recomment not too high speed or constant speeds for long periods for the first 500 miles or so.

Just do what the manual says. If it says to avoid usiong full throttle and run at low RPMs, then do that.

If it’s not specific about what constitues “low rpms” then it probably doesn’t matter, as long as you don’t “thrash” it

That question came up on “Car Talk” and the brothers split on the decision, one favoring the take it easy approach, and the other going with the ‘run it hard from the start’ school of thought.

I wouldn’t worry about it at all, unless you are the type that holds it in 2nd gear and hauls out from a stop at 7000 rpm it’s pretty hard to hurt an engine these days. Just drive.

I can’t come up with a good reason to avoid high loads at low rpm’s, and it may be beneficial. What I recommend is to vary the rpm’s w/i the lower end of the scale. The idea is to avoid wear patterns from a single RPM ‘speed’. This also applies to vibrational wear. This vibrational wear might be the reason to sometimes load the engine (changes the vibrational frequencies of the engine, and force distrubuted in the engine, which could also alter vibrational patterns).

Possible, but I think it’s a holdover from other times. Engines that are proven designs seldom have sharply defined resonances within their operating range of RPM. Furthermore, four cylinder engines use 5 main bearings, the block casting go below the centerline of the crankshaft and they are in general much stiffer and sturdier than in past years.

Do you plan on keeping the car until the engine dies? If not, then there’s nothing to worry about. Any engine should give you a normal service life no matter how you break it in. If you break it in wrong and sell it at 160,000 km, it’ll be the next guy’s problem anyway.

Unless he’s able to detect abnormalities and proposes to adjust the purchase price accordingly.

And you’re an inconsiderate person.

No, I’m not inconsiderate and no, there won’t be any abnormalities. Most cars don’t make it to the junkyard for engine problems; why does everyone always worry about their oil and their break in periods? If you hear about problems, it’s because someone blew a head gasket, or someone punctured a cylinder because something fell into the engine. The biggest wear item in the engine is the cylinders, rings, and heads (cylinder wall). There’s nothing much to break in here these days. Yeah, maybe there’s a possibility that after 300,000 km you’ll need new rings, but at that point it doesn’t matter whether you’ve driven like an old women or a 17 year old. They’re old and have had a lot of wear.

To prolong the life of your car, the best thing you can do is not crash it. Take care of the body. Make sure your tranny doesn’t fall apart. Electronics are likely to fail. Emission systems are likely to fail. You may need an alternator. Or a fuel pump. Vacuum lines fail. A/C compressor. Cooling system. These are all things you need to worry about in selling you car. Your engine is the thing that’s absolutely the least likely thing to ever fail. Keep in mind when people say “engine failure” they often don’t mean the engine per say, but associated components.

Of course take the above with caution – look up you engine history. Certain engines have problems that are inherent to thier design. But again, these are usually non-/minimum-wear items.

Try to consider all of the pieces of junk cars you’ve ever heard of being retired for service. Where was the problem specifically?

In the grand scheme of everything that could possibly go wrong with your car, the engine is a very minor concern.

And forgive the stupid “per say” typo!