Engine break in

[Jim M]

There is a thread on JU about synthetic oils. In the post the originator asked if synthetic oils were good and that he had switched at 3k miles from dino to synth. My reply was that he should wait until the engine was broken in before switching, which was immediately slammed in the next post to say that his engine was fully broken at 3k miles.

My question here is about engine break in, not he pros and cons of synthetic oils. So here it is, how can one tell when an engine is fully broken in? My experrience is severly limited in this area as I have only ever had three new engines under my care. I have always used fuel economy and, largely, seat of the pants analysis to determine when the engine was fully broken in. In my TJ, the 4 cylinder steadily improved in mileage and seat of the pants power until almost 8k miles. The BMW 4 banger I had took about 4k miles, and the Isuzu V6 only took about 1500 miles. What measurements can be taken, what data gathered, or what common knowledge cn be applied to truly determine when a new or rebuilt engine is fully broken in? Also, what else happens during break in besides the seating of the rings?

__________________
97 TJ. Not stock.

There is no bolt on kit called driver skill. If you want it, you have to actually go out and drive...offroad.

[TJRON]

I don't know the answer but I've always heard 10K just to make sure everything is really the way it's gonna be. That's about 3 oil changes.
Ron

[mrblaine]

I am with Ron on this one and agree with you that they do take a while for everything to thoroughly seat. On way to do it might be continual compression checks. Start new and add the synthetic when they level off.

This is like most stuff out there, a whole bunch of speculation and hearsay, but very little fact.

I am also wondering if the cars that spec Mobil 1 are broken in or built differently than others.

It would seem if your theory is correct, and I agree that it most likely is, that those motors would be built differently.

It is not who you know, It is who knows you
Jeeps do not make jeepers, jeepers make Jeeps.
Which is more important, the degree or education?

[Richie]

Engine break in times will definately vary. This is mostly due to the composition of the engine rings. A cast ring will seat sooner than a moly or chrome ring. I work in an engine shop and can't tell you what you could check externally on the engine that would indicate break in is over. I know that fuel milage will gradually increase as break in ends. This is probably the easiest thing to monitor. I can tell you that I've torn down a cat diesel that did not appear to be fully seated in at 7000 miles, but a cat will go 500,000 before a rebuild.

Richard
97 TJ with sprinkles
97 ZJ

[Stu Olson]

<BLOCKQUOTE><font size="-1">quote:</font><HR>Originally posted by Richie:
I can tell you that I've torn down a cat diesel that did not appear to be fully seated in at 7000 miles, but a cat will go 500,000 before a rebuild.

[/quote]

Now I could get into having one of those under the TJ's hood!

If you're gonna play, you gotta pay
http://www.stu-offroad.com

[Tumbleweed]

Stu, did you realize that at one time you could get a diesel in a Jeep, from the factory?
Here is a CJ6 on ebay with the Perkins diesel in it.
http://cgi.ebay.com/ebaymotors/aw-cg...item=598318793

[Stu Olson]

Given the length of time that Jeeps have been available, that does not surprise me.

I gotta find me one with a post hole digger on the back. I have no need to put in fense posts....but I think it would make one heck of a winch point anchor....sink it 3 or 4 feet and away you go!

If you're gonna play, you gotta pay
http://www.stu-offroad.com

[Hellbender]

http://jeepbbs.atinfopop.com/4/OpenT...5&m=4524090451

2000 TJ 4.0L, A/T, all factory options.
Jeep Rater Score 360
http://www.hellbender.rockcrawler.com/
NRA Lifetime Member

[Hellbender]

On Topic----I changed to Mobil 1 at 3000 miles (2nd change) my rig uses NO oil (visible on stick) between changes (3-4000 mi.), BUT, my rear main seal started leaking very slightly almost immediately after the change. I also went to synthetic in the A/T and the rear tranny seal started leaking there, too. Might be coincidence (bad bunch of seals or a common problem), might not. I'd say switch at 10,000 miles.

The motors that come w/ synthetics are "new generation" (post-CAD), built to much different tolerances than our "old generation" (pre-CAD) stuff.

2000 TJ 4.0L, A/T, all factory options.
Jeep Rater Score 360
http://www.hellbender.rockcrawler.com/
NRA Lifetime Member