Paging MadBill! Engine break-in question...

[ragingfish]

To MadBill (or anyone else who knows this stuff):So I'm thumbing through the OM of the 'rents new G6. Of course, it has the universal standard break-in period: 500 miles for the engine, and warns not to travel at any one set speed, fast or slow.Every car I've ever owned had the same break-in method. 500 miles, varied speed.Why is that? How does varying the speed affect break-in of the engine whereas cruise-control-moderated speed would not?

[MadBill]

Ahem! You paged, Mike?The reason for the suggested varying loads and speeds is as follows: The load distribution on various engine parts changes depending on the throttle opening and RPM. For example full throttle and low RPM gives quite a workout to the bottom half of the main and rod bearings and heavily loads the piston rings against the bores, whereas high RPM & light throttle puts more load on the top bearing halves and gives high sliding velocity for the rings but low contact loads. Short periods of full throttle loads the rings and pistons against the bores to speed break-in without allowing time for excessive heat build up. The reality is that most modern engines will survive pretty well any kind of driving from day one (a Good Thing if you've ever seen a dealer's 'throttle jockey' flat-footing it down the highway delivering someone's brand new, soon-to-be-pampered baby! ), but for the sake of a few hundred miles, why take chances?BTW, brakes, gears, etc. also benefit from this initial gentle touch...

[ragingfish]

Awesome info man!Thanks for your ingeniousness as always!

[scherry2]

Quote, originally posted by MadBill »The reality is that most modern engines will survive pretty well any kind of driving from day one (a Good Thing if you've ever seen a dealer's 'throttle jockey' flat-footing it down the highway delivering someone's brand new, soon-to-be-pampered baby! you should see them driven at the factory.

[rubberman]

Quote, originally posted by scherry2 »you should see them driven at the factory. Yeah I seen some at the truck plant in Oshawa foot right to the floor tire spinning etc.The old saying drive it let you stole it or its not mine