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Mechanic's Corner

Engine break-in

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Most every one, at one time or another has been told the “best” way to break-in the engine of your new car or light truck. Some say no break-in is necessary; others say push it hard from the very beginning, 500 mile break-in, 3000 mile brake-in – who is correct!

As times have changed engine technology and engine machining abilities have changed. As a result the recommend break-in procedure has changed with the times. Older cars required a longer break-in period (up to 3000 miles) than our newer cars. Because our new engines have better machined cylinder bores, higher tension piston rings and over all more precise build tolerances most manufactures advise only a very modest break-in period of 500 miles (check your owner’s manual for specific recommendations).

During the breaking period you should avoid full throttle acceleration and constant engine rpm. It is generally agreed that varying the engine load (speeding up and slowing down) while avoiding full throttle acceleration is the best way to break-in these technologically advanced engines. The worst thing you can do to your new vehicle is to spend the first 500 miles of its life cruising down the freeway at 70mph!

The push-it-hard-from-the-beginning school of thought generally comes from those involved with high performance air cooled engines. These smaller engines tend to expand and contract when warm more than the larger water cooled engines in our cars and trucks. As a result they can benefit from the increased pressure exerted on the piston rings during hard acceleration. Remember the goal of breaking-in and engine is to “seat” the piston rings. A certain amount of piston ring pressure on the cylinder walls is necessary to accomplish this. The larger engines can generate the needed pressure without the wide open throttle acceleration.

As the rings are seating very small bits of metal are knocked off of the cylinder walls. This creates the very smooth surface necessary for the oil on the cylinder walls to be scraped off before it is burned during the combustion process. Most manufactures do not recommend changing the engine oil at the end of the break in period. The theory is that the oil filer will catch the metal dust generated during the break-in period. Considering the extended oil change intervals now being recommended I would say get that first oil change around the 2000 mile mark (unless you manufactures says less!) After that you should follow the manufactures recommendations.

Proper engine break-in will generally lead to reduced oil consumption during the life of the engine. But as the miles accumulate, carbon can build up on the pistons and rings diminishing their ability to scrape the engine oil form the cylinder walls resulting in increased oil consumption. After break-in is complete, occasionally pushing the engine hard (wide open throttle acceleration) can help keep these carbon deposits from building up. You all know the story of Grandma, who only drives to church on Sunday…   Not good for the engine!

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  • Visitor, August 21, 2011, 17:07

    I have a 1997 ford explorer sport 4.0 sohc I just had it rebuilt and on start up it sounds great but about 30 seconds later it starts to rattle can u tell me what I might be dealing with.

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