[HwnMurano]

Can you tech / mechanical guru types please tell us about what exactly is going on with the MO's engine and trannie during the "break in schedule"?

I noticed that the manual says not to drive over 4,000 rpm, don't accelerate at full throttle, avoid quick starts, avoid hard braking, and no trailer towing for first 500 miles.

Over the years of owning several new cars, I can recall people saying that the break in period allows the insides of the engine to smoothen the still "rough edges" of the machined internal moving parts. It also avoids placing excessive stress on the various parts like cams, valves, cylinders, gaskets, etc., until such time that the engine has become "seasoned" to hold up under high rpm, fast braking, towing heavy loads and other high stress conditions. All this was hearsay from non-mechanics.

What is fact and what is fiction here? Thanks in advance!

 

[ekaxel]

IMHO (and I stress IMHO!), break in was a lot more important in "the old days" than it is today. Modern machining techinques produce a much better "fit", and modern lubricants, lubricating systems and filtering do a overall much better job.
All I do personally is change the oil and filter at 1000 miles (and replace with synthetics at 2500). I would change the tranny fluid if it was a conventional automatic too.

 

[hfelknor]

Most parts don't need "break in".
Bearings for instance are never going to be better than the very first time they turn.
But some parts do.


In the engine for instance, when we built a race motor, we broke the motor in on the test bench with "maybe" a couple of hours of running at various RPMS. But we weren't doing it to break in the motor, we were adjusting for throttle response, etc.
And of course, we didn't care if the engine went bad at 20000 miles, we were going to rebuild it at 1000 miles or less.

But in the engine there are some things that can help an engine last a long time.

One are the rings, both compression and oil.
When these are placed on a piston, they are free to rotate around the piston.
It would help if they stayed in one place.That place being where ever the maximum seal is located.
So as you break in your Murano, the rings will slide around until one time they will cool down and take a "set". If you don't rough house the motor too much after that, the set will become permanent.

The other part that many people screw up is brakes.
Far too many complaints on these boards about brake shudder and having the rotors turned.
All could have been avoided if the brakes had been broken in properly.

Again, in racing, we would SET those suckers hard.
But again, we would rebuild the brakes EVERY race.

To get long term satisfaction out of your brakes, then apply them long and slow for the first x miles. (Obviously if you take the car out on a track and circle the track (slowly) for 100 miles, and then come in, you have braked exactly once.
OTOH in town you could be on the brakes every 50 ft.
The whole idea is brake early, and apply them looonnnnnnggggg and slow.
Maybe 200 reps and your brake pads will be set (w relation to the rotor).

IMHO those are the two biggest points of break in.


Qualifications
Have never been a mechanic.
Drove and did a little wrenching on GN super modifeds, Part time crew member in the Toyota Atlantic Series, part owner of super modified and Bush series (Maloney Racing)


Homer

 

[Kris]

Look at this posts: engine break in

 

[Eric L.]

I thought it had something to do with seating the piston rings. If you drive very aggressively the rings may not seat correctly, leading to increased blow by (and lifetime oil usage).

 

[Tyler_Canada]

A lot of why you take it easy at first, especially on the brakes, is heat cycling the parts. You want to gradually get the parts to hotter and hotter temperatures, so that the metal can get used to it without warping.