With manufacturing tolerances what they are these days is a break-in period still relevant? I'm guessing we get a variety of opinions, so please include your rationale if you say no, and your thoughts on the "right" way to do it if you think yes. Thanks

 

The manual shows 1,000 miles break-in for the drivetrain and other information.

 

I'll bet the 1000 mile break in statement has been in every owners manual since the 50's.

The reality for the engine is modern rings, bearings etc. need little if any break in.

Race engines are usually run initially to check for leaks and then it's full out on the track.

I have no idea what MB does but decent race shops have all the gears in the transmission, rear end etc. coated with a film which does not require any break in. The break in on my dragster drive train was do a burn out and then a full throttle pass. I never had a premature failure and I must have had 25 engines and 6 chassis with new drive trains over the years I was racing actively.

The only thing that currently requires a break in are engines with solid lifters. Even these are good to go in about 15 minutes of running. The buckets on an overhead cam engine may fall into this category.

I suspect what may need a 1000 mile break in is the driver. People coming from slower/different configuration cars may need an adjustment period to keep the car on the road and away from fixed objects.

The other old wives tale is the idea you should change the oil after a small run time. Yes the engine may have some trash in it but that is what the oil filter is there for. A decent filter removes all the harmful pieces in the oil on every oil pass through the engine. The only possible trouble is if you left so much trash in the engine while building that the oil filter becomes clogged and the filter is bypassed with the relief valve. This is unlikely with any OEM manufacturer of engines as it is with any race shop. If the filter does clog it's probably a good thing to blow the engine early on as obviously the assembly process and /or cleaning process was done incorrectly and it's a lot better to have a failure early under warranty.

I suspect a lot of this break in/oil change stuff has been passed down from the days when cars had plug fit pistons, bearings, ran overly rich when cold with a carburetor and had and no oil filter.

 

Agreed!

 

With this kind of an investment, I'll stick with the manufacturers recommendation.

 

I just did a road trip - knocked out the 1000 mile break-in period in two days...

 

About 4 days for us...

 

Perfectly assembled engines should reasonably require less break in. Unfortunately, engines are mass produced and clearances vary a) within allowable manufacturer's range and b) sometimes outside of manufacturer's stated limits. Mistakes happen, even at Mercedes-Benz engine assembly plants.

I have never read an SAE or any other technical report that examined what impact, if any, various break in procedures have on the very long term engine performance and reliability. Perhaps the cost is too great, or the results have simply not been released.

I chose to follow the owner's manual instructions on how to treat the engine during the first 1000 miles. Being a bit gentle seems unlikely to do harm, and conceivably might help the engine to cope with any unexpected manufacturing variations. Having seen precision, high cost, aircraft engines blow up on the initial test stand operation has made me cautious.