Best Practice: Breaking in a new engine

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SigQAEngineer

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Gents:

What is the best practice for breaking-in an engine one a brand new vehicle (not rebuilt) ?

In addition to following owner's manual & vary the drive speed, is it necessary to properly seat the oil rings by driving under a higher gear & high load condition for the new engine ?

Basically, should a new engine be driven hard or baby it for a while ?
 
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Follow the owners manual. Most say not too hard, not too soft, and to vary engine rpms a lot during the first few hundred miles. ie, don't set the cruise at 50 mph during breakin.
 
Vary speeds and loads.Never "lug" an engine down.Sometimes baby the acceleration,sometimes step on it.But dont thrash it.
 
The old, old school logic said "drive it like you stole it," or "drive it hard at first or you'll never be able to drive it hard again," when it came to breaking in a new engine. That has not been good advice for quite a few years now due to improved manufacturing, improved metallurgy, improved design, and improved lubrication. Nothing else is required other than what the manufacturer recommends. There's really nothing you can (or should) do "above and beyond" those recommendations, because there really is nothing "above and beyond" to do. Exceeding the recommendations outlined by the engineers could well result in higher wear and no long-range benefits. But doing what the engineers recommend is unlikely to cause any long-term problems or issues. There's a lot of old-school advice and old-school thinking around here, but the old days of having to re-think engine and oil design are in the rear view mirror. Competition and profit margins are too tight to give less than ideal advice in a manual these days.
 
Here's what the owner's manual for my ATS says. It echoes the thoughts already expressed:

- Avoid full throttle starts and abrupt stops.
- Do not exceed 4000 engine rpm.
- Avoid driving at any one constant speed, fast or slow.
- Avoid downshifting to brake or slow the vehicle when the engine speed will exceed 4000 rpm.
- Do not let the engine labor. Never lug the engine in high gear at low speeds. With a manual transmission, shift to the next lower gear. This rule applies at all times, not just during the break-in period.
- Check engine oil with every refueling and add if necessary. Oil and fuel consumption may be higher than normal during the first 2 414 km (1,500 mi).
 
We broke both cars in moderately hard, and they run fine. There was a good bit of 75% throttle applied during the first few hundred miles. We waited until about 500 miles to do any real WOT, though.

Definitely do not baby the engine. Do not give it WOT for the first few hundred miles if you can avoid it, either. Do give it some decent throttle application, especially going uphill or accelerating to highway speed.
 
My Durango manual (Pentastar V6) says drive moderately but that brief full throttle accelerations contribute to a good break in. Doesn't give a mileage threshold when to do it (I.e. not before 500 miles).
 
On piston aircraft engines, after the maximum allowed, ground idle time of 30 minutes (for leak checks) we fly as close to full power as temps allow, until the rings seat. Generally 45 minutes to 3 hours.

It's obvious when this "ring seating" occurs, as the cylinder head temperature drops markedly. And, since we have individual CHT indications, we can tell when all cylinders are broken in.

The UOA clearly shows higher metals after the first 5 to 10 hours. From the ring seating. Probably a bit of stuff from assy too. But after that, wear metals remain mostly constant for the life of the engine.

Note: Lycoming aircraft engines have nitrided steel cylinder bores that are considerably harder than automotive cast iron bores. Also, chrome faced rings.


I'm fully aware that modern automotive engines are not antiquated, air cooled, low RPM, high BMEP engines. But, I do think there is some parallel. Ring seating occurs during periods of heavy load. Managing ring temperature is a function of managing RPM's and duration of load. Just like on an aircraft.

My method has always been to limit RPM and duration of heavy loads. But to apply increasing loads over time. And to allow parts to heat cycle, by letting them cool overnight if possible.
 
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I don't think on a modern car it matters. Think about it 99% of new car buyers never crack the manual and just drive them normally.

Most of those cars just see semi regular quick lube services and end up in the junk yard 15 years later or whenever.

So it doesn't matter.
 
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I would do the first oil change early, like under 1000 miles.

There is always some amount of fine metallic debris in the oil on a newly built engine.
 
Originally Posted By: Rock_Hudstone

I would do the first oil change early, like under 1000 miles.

There is always some amount of fine metallic debris in the oil on a newly built engine.


And you believe the manufacturer didn't account for this when they suggested the initial oil change mileage? There's fine metallic debris in all engine oil at some point. If they thought under 1000 miles was going to keep them from a warranty claim, why didn't they suggest doing that?
 
best practice in what?

Just follow the owner's manual, drive and change oil. No need to lose sleep over an already pretty much "broken in" engine.

Q.
 
Quote:
And you believe the manufacturer didn't account for this when they suggested the initial oil change mileage? There's fine metallic debris in all engine oil at some point. If they thought under 1000 miles was going to keep them from a warranty claim, why didn't they suggest doing that?


I think it is mainly to save the owner the maintenance costs of early oil changes.

While I don't think it is critical, I prefer the first oil change within the first 1000 miles.

Like Q said,

Quote:

Just follow the owner's manual, drive and change oil. No need to lose sleep over an already pretty much "broken in" engine.

Q.
 
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Originally Posted By: SigQAEngineer

Basically, should a new engine be driven hard or baby it for a while ?


1 Drive easy and vary speeds for first 100 miles.
2. Change factory fill oil at 1000-1500 miles (exception: Hondas run at least 5000 miles because honda puts high moly assembly fluids in the factory fill)
3.I don't run an engine hard until after 3-5000 miles.
 
Originally Posted By: sciphi
We broke both cars in moderately hard, and they run fine. There was a good bit of 75% throttle applied during the first few hundred miles. We waited until about 500 miles to do any real WOT, though.

Definitely do not baby the engine. Do not give it WOT for the first few hundred miles if you can avoid it, either. Do give it some decent throttle application, especially going uphill or accelerating to highway speed.

On virtually all vehicles, 75% throttle opening equals at least 95% power...
 
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