I was reading my Haynes manual and read the procedure for breaking in a new or rebuilt engine (for the Xterra, Frontier etc). It advised driving the truck in an open area and accelerating from 30 to 50 MPH and then letting the vehicle rapidly slow to 30 MPH (I am guessing using engine braking) to seat the pistons. This is to be repeated 10-12 times consecutively. The vehicle should then be driven gently for the next couple of hundred miles with an oil/filter change at 500-600 miles. Haynes then suggests driving the truck neither aggresively nor gently for the next few hundred miles. They consider the engine broken in at approx 2000 miles. That is the most comprehensive "break in" information I've read so far. What have YOU done?

I kept the RPMs below 3500 & did not go over 65 MPH for the first 1,000 miles. Other than that I just drove as the traffic flow would allow as I do anytime I drive an automobile. The Nissan recommendation from the manual says to not drive the same speed for periods at a time. I find/found this hard to do and really does not make sense. I'd hate to be behind a guy going from 30 to 50 to 30. I did the first oil change at 3,200 miles (Nissan recommends 3,750 mile intervals). If you have money to burn--it can't hurt to change your oil as often as you like.

well, with only 300 miles on the odo i am still breaking in. i think that the way you use your brakes is important too. if you can avoid panic stops i think it's better for them.

as for the engine, i plan on mobil 1 at about 1500 miles with the thinking being that my break in period will be pretty much over by then and then again every 3k miles. i have a friend who is a former racecar driver and his position on breaking in an engine was to drive it exactly like you would if it were already broken in, so that it would get used to things that way. i tend to trust the auto mfgs more than his approach, but thought i'd throw out what he used to say about breaking things in.

The reason they want you to vary the engine speed and to coast etc. is to vary the vacuum in the system to help pull oil up into the rings and such. It's good advice.

Brent

I made a point of driving my new X home on a secondary road with lots of hills, stop lights, etc.
The dealership did their part by delivering it to me with the manual hubs in the locked position On the way home, I was telling myself I know these things are tight and slow when new but jeez.... The next day I found the hubs were locked

1700 miles now and it is just gets stronger and faster.

On my 500 mile drive home from the $tealership (possibly the worst thing one can do is exactly that - I made sure I took more stops than usual and nver went over 65 MPH) I made a very conscious effort to vary my speed - my apologies to anybody who was behind me that day from Buffalo to Long Island. As others have said, it is good for both ring sealing and for pulling oil up to the top of the motor.

I changed the oil at 500 miles, 1000 miles, 2000 miles, and again a 3000 miles, with routine 3K intervals after that. I used the Nissan OE filter and the a name brand 5W-30 oil, per the manual. At the next oil change (9K) I plan on switching to synthetic (most likely Mobil 1) and maintaining the 3K interval.

One can never hurt a car by over-maintaining it - with that kind of treatment my last Nissan truck went over 350K before it finally rotted away.

What about supercharged engines? The system isn't always under vacuum, but positive pressure. How does oil get up to the rings and such then? I think they want to you to vary speed so that you don't wear grooves in whatever parts breaking in. They'll wear-in more evenly? What do you think?

There is always vacuum, even in supercharged engines. Do you think the air charge is pushing the piston down on the intake stroke?

I'm sure there are wear issues, that's the whole point of the break-in. If the engine spends all its time under a consistent load, only certain areas would receive the majority of the wear.

Brent

I do not think the positive pressure is pushing the piston down. Do you believe vacuum is pulling the piston down on the intake stroke? I believe the piston is pulled down by the crankshaft as other cylinders fire. They do not all move up and down in sync.
There is not always vacuum in a forced induction engine. There is positive pressure when the supercharger is cramming boost into the cylinders.

I did the same thing I always do on a new engine...Load it as hard as possible, and drive it like I intend to use it (after it is at operating temp of course...). This practice has never left me stranded with a bottom end failure in 12 cars and 700,000+ miles. I have read the same haynes manual - it is ok advice, though I just do things this way as I have seen many engines running on a dynomometer after a fresh build at full load - and watched the crankcase pressure go down and down as the rings seat, conversly I have seen engines that were dyno'ed at a later date (after insufficient break-in) to find that the rings will rarely ever seat (and keep the same relative crankcase pressures) as an engine that was properly loaded initially.

BTW: I have 10,000 miles in 6 months on the X an it burns no oil, has great power, and overall runs like a champ...as well following only the Nissan service oil change guidelines.

In Brent's defense the combustion chamber of an Ineternal Combustion engine ALWAYS has a vacume on an intake stroke. A supercharger just helps rush more air in during the intake (reducing the vacume and cramming more air into the cylinder).

How Stuff Works

However I don't see how vacume would bring more oil up past the rings, the whole purpose of the top two rings is to keep oil from getting past.

One of the things I remember reading abut the Xterra in the sales brochure that Nissan sent me is that the pistons and cylinders are mirror polished from the factory.

Since the purpose of breaking in an engine is to polish the cross hatching off of the cylinder walls its seems to me that the Xterra engine would already be "broken in".

But I guess the rest of the engine and drivetrain need to be broken in too.

How can there ALWAYS be vacuum on the intake stroke, when a supercharger compresses the incoming air stream? When the cams lift the valves, the pressurized air is forced into the cylinder (by positive pressure). It is not drawn in by vacuum. When the charger is not producing boost, the pressure is diverted via the bypass valve and, vacuum of the intake stroke draws in air. (Idle, cruise, light throttle, etc)
Logical?

i just drove mine the way i wanted to drive it
i have 1300 miles and ive been up to 80+ miles per hour and have raced the engine some showing off to friends. if it breakes it breaks that is what warrenty is for.

my understanding has always been that the possible damage that can occur from not breaking in properly is the type that is long term...not the type you'd see within the warranty period, necessarily.

I figure that if it was a BIG deal Nissan would put more emphasis on it in the manual...and be more specific.