Okay, what's the truth about engine break-in?

Those people will get a pretty quick and expensive education!

Are you saying that with a bit of tongue in cheek Ray? That web site uses Honda F3 (600cc) motorcycle engine pistons as an example. That is not really a fair comparison IMHO. Honda uses a completely different metallurgy for their CBR engine sleeves and rings than a mass produced, street auto engine. That is partly how they can get a 11500 rpm red line out of that motor. He is absolutely correct for the motorcycle application. I have owned and pulled apart many.

I am only aware of one manufacturer (Aprilia) that fills new motors with synthetic oil, and it does hinder a timely break in, IMHO. New model sport bike motors are some of the highest internal combustion engine technology, money can buy. Some exceeding aircraft quality. Incredible power to weight ratios result in a high performance package you can purchase for street use. Some will nearly travel 200 mph out of the box and acceleration almost second to none.

The method is no different for other engines.

It seems that the aircraft engine industry get it right at least :-)

Many instructions agree that synthetic oil should be avoided during ring break-in, but is recommended later.

My guess is that an old rental car would probably have good ring seal :-)

Seems to me that you should follow the vehicle manufacturer's recommendation. Toyota usually says things like:

"Break-in period

"Drive gently and avoid high speeds.

"Your vehicle does not need an elaborate break-in. But following a few simple tips for the first 1600 km (1000 miles) can add to the future economy and long life of your vehicle:

• Do not drive over 88 km/h (55 mph).

• Run the engine at moderate speed between 2000 and 4000 rpm.

• Avoid full-throttle starts.

• Try to avoid hard stops during the first 300 km (200 miles).

• Do not drive slowly with the manual transmission in a high gear.

• Do not drive for a long time at any single speed, either fast or slow.

• Do not tow a trailer during the first 800

Nissan says things like:

"BREAK-IN SCHEDULE

"CAUTION

"During the first 1,200 miles (2,000 km), follow these recommendations to obtain maximum engine performance and ensure the future reliability and economy of your new vehicle. Failure to follow these recommendations may result in shortened engine life and reduced engine performance.

• Avoid driving for long periods at constant speed, either fast or slow, and do not run the engine over 4,000 rpm.

• Do not accelerate at full throttle in any gear.

• Avoid quick starts.

• Avoid hard braking as much as possible.

• Do not tow a trailer for the first 500 miles (800 km). Your engine, axle or other parts could be damaged. .... "It is normal to add some oil between oil maintenance intervals or during the break-in period, depending on the severity of operating conditions.

Ford says things like:

"BREAKING-IN YOUR VEHICLE

"Your vehicle does not need an extensive break-in. Try not to drive continuously at the same speed for the first 1,000 miles (1,600 km) of new vehicle operation. Vary your speed frequently in order to give the moving parts a chance to break in.

"Do not add friction modifier compounds or special break-in oils during the first few thousand miles (kilometers) of operation, since these additives may prevent piston ring seating. See Engine oil in the Maintenance and Specifications chapter for more information on oil usage." .... "ESSENTIALS OF GOOD FUEL ECONOMY

"Measuring techniques

"Your best source of information about actual fuel economy is you, the driver. You must gather information as accurately and consistently as possible. Fuel expense, frequency of fill-ups or fuel gauge readings are NOT accurate as a measure of fuel economy. We do not recommend taking fuel economy measurements during the first 1,000 miles (1,600 km) of driving (engine break-in period). You will get a more accurate measurement after 2,000 miles-3,000 miles (3,000 km-5,000 km).

Honda says things like:

"Break-in Period

"Help assure your vehicle's future reliability and performance by paying extra attention to how you drive during the first 600 miles (1,000 km). During this period:

• Avoid full-throttle starts and rapid acceleration.

• Avoid hard braking. New brakes need to be broken-in by moderate use for the first 200 miles (300 km).

"You should follow these same recommendations with an overhauled or exchanged engine, or when the brakes are relined."

GM says things like:

"New Vehicle Break-In

"Notice: Your vehicle does not need an elaborate break-in. But it will perform better in the long run if you follow these guidelines:

• Keep your speed at 55 mph (88 km/h) or less for the first 500 miles (805 km).

• Do not drive at any one constant speed, fast or slow, for the first

500 miles (805 km). Do not make full-throttle starts. Avoid downshifting to brake, or slow, the vehicle.

• Avoid making hard stops for the first 200 miles (322 km) or so. During this time your new brake linings are not yet broken in. Hard stops with new linings can mean premature wear and earlier replacement. Follow this breaking-in guideline every time you get new brake linings.

• Do not tow a trailer during break-in. See Towing a Trailer on page

423 for the trailer towing capabilities of your vehicle and more information.

"Following break-in, engine speed and load can be gradually increased."

The common themes seems to be that for the first 500 to 1000 miles -

• Don't drive to fast (55 mph seems arbitrarily slow)

• Vary speeds

• Avoid full throttle operation

• Avoid hard stops

• Don't tow

Ed

Somewhat tongue-in-cheek. I have always broken in cars pretty much the same way. I used to pick up my company cars at the port of entry, hit the highway a couple of miles after exiting the gates, and then put about a thousand miles a week of mostly highway driving. Steady high speeds never hurt any of my cars.