Engine break-in required??

[Paul Jenkins]

New Vue owner here, 4cylinder-manual transmission...

The manual says to drive the car 'easy' for the first 500 miles or so to break the engine in. Don't drive at one RPM for any length of time and don't rev the engine to redline, hard starts, etc.

Why is this needed? I thought an engine had 90% of its wear in the first 10 minutes of running, the other 10% over the next X years of running. That's what they used to say when you rebuilt a small block 350 Chevy anyway...

Can someone explain the technical reason(s) why you have a magical 500 mile break-in period?

Thanks,
Paul

[manualman]

It's a matter of how conservative you want to be.

Probably, you'll be OK whatever you do. But the reason they want you to keep the speed down, vary the revs and not "get on it" immediately is to give the piston rings the best chance to get a perfect seat to the cylinder liners.

This can mean the difference between a car that goes 200k miles without using oil between changes and one that burns a quart every 1,000 miles.

Given Saturn's troubles in the past with oil control rings, I'd say give that new engine every advantage you can.

In that same vein, I also change my oil for the first time at about 1,000 miles. Those first few miles smooth out the rough edges on all the moving parts. Might as well get all that stuff outta there ASAP.

[Paul Jenkins]

manualman, thanks for the response...

however, can you explain how the piston rings seal? And how they seal better by NOT running the engine speed at the same RMP and not pushing the RPM limits?

I'm not saying I want to push the Vue 4 cylinder to redline, I think that is dangerous any time, not just when you first buy the car (otherwise, why would it be a 'redline'?), but varying the engine speed a lot doesn't make sense to me in aiding piston ring seals (which, I thought, again, are sealed within the first 10-30 minutes of engine startup, which is done @ the factory...)

[manualman]

I'm neither a mech engineer nor a mechanic. However, I have heard this from both the Saturn owner's manual and from the Car Talk guys. That's good enough for me.

How could it be? I'm guessing that since perfect machining has yet to be invented, all rings have some small irregularities when new. Therefore, the protruding irregularities can actually poke through the oil film on the cylinder walls and wear themselves down until the ring is custom fit to the cylinder wall. During this process I can see why you would want to keep the revs low and limit the amount of gas/air it gets. No idea why constant revs would be bad for this, but maybe that's why those guys get paid more than me.

[ricksLS1]

If that's what they tell you to do .. Do it! Want the engine to break in correctly

[Paul Jenkins]

Originally posted by ricksLS1
If that's what they tell you to do .. Do it! Want the engine to break in correctly

I'm not saying I will not do it, just asking WHY :)

[Phil]

Every new engine takes some breaking in, and caru magazines have found that "green" engines post slower times that ones that have been run a bit. The exact physics of engine break in escape me, however. I would change the oil once you clear the break in period (recommended or not), and drive happy.

[moondogb]

manualman is right on about irregularities in cylinder and ring shapes, especially in mass production. I overhauled light aircraft engines for 12 years before my airline work and I can tell you this about ring seating. Rings, particularly compression rings, are forced against the cyl. wall by tension and BMEP [brake mean effective pressure] pushing them outward from the ring grooves. More RPM, more pressure, more friction = more heat. It's possible to get a new engine so hot from friction that it can destroy the temper of the rings, or cause a hard glaze to form on the cylinder walls. As to varing the RPM, this serves to chage BMEP, MAP and crankcase pressure which lets oil get sucked and pulled in to the cylinder areas. I'm sure modern production engines aren't near as critical on breakin as overhauls but if you have to drive a little out of style for 500 miles, whats the harm? I ain't no engineer, just play the game by the book. Enjoy your Vue, they look like a winner!! Tom B

[Qlara]

Good explainations in some posts.
Even though modern engines are no longer require specific Break-in procedures these days, it's always good to follow what the Manual mentioned: Don't drive in one speed (= RPM) in the first 500 miles. Varied the RPM and Speed to let the engine gone through the break-in period and be fine.

If possible, make your first oil change a bit earlier than scheduled......maybe 2500miles. :yes:

[Heartbeat - '95 SL2]

As for avoiding constant speeds and RPMs during break-in, apparently the reason is to prevent the buildup of varnishes which occur under those conditions.