Properly breaking in your vehicle's rebuilt engine is essential to the engine's longevity. The initial 500 to 1,000 miles of an engine's life determine how long the engine will last, how much oil it will consume and how well it will perform. Breaking it in improperly can result in a seized engine or an engine that runs poorly, burns oil and has a short lifespan. Luckily, breaking in an engine is a relatively simple task. Although some engines may have special needs, this guide covers most gasoline-powered cars, trucks and motorcycles.
Start the engine and let it run for about 5-10 minutes to reach operating temperature.
Drive the vehicle, avoiding full-throttle starts, constant speeds and "lugging" the engine (allowing the car's RPMs to decrease while strain on the engine is increasing; for instance, trying to climb a steep hill in fifth gear in a manual transmission vehicle). Stop-and-go traffic is best for this; long trips on the interstate are not. The idea is to constantly vary the engine's speed, which allows newly machined parts inside the engine to adapt.
When the vehicle reaches 500 miles, have the oil and filter changed. Most manufacturers recommend using regular, not synthetic, oil for the break in period. Be sure to check with the mechanic who rebuilt the engine to see what type and viscosity of oil are recommended as this varies from engine to engine.
Drive the vehicle, following the instructions in Step 2, for another 500 miles. Have the oil changed again and the engine will be suitably broken in.
