Engine Break In

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Dec 7, 2001 | 06:30 AM

lastchance

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From: South Central PA

Engine Break In

Dec 20, 2001 | 11:51 PM

C Davis

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Joined: Nov 2001

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Engine Break In

I am about 4000 miles into my newly rebuilt 302 2bl. carbed 83 XLT. I am very happy
with the motor so far, (aside from my hissing brake pedal which I have concluded is
the brake power booster) which I will fix soon.
My question is this:
The best I have been able to muster gas mileage-wise is 10.6 MPG, and I was thrilled
because I have been consistently getting 9.4. I have heard more than one person tell
me that as my engine breaks in, my MPG will increase. Who has had experience with
this phenomenon after an engine rebuild, and could someone tell me why this
happens?

Thanks,

C. Davis

Dec 21, 2001 | 01:10 AM

chaser

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Joined: Jun 1999

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From: Tallahassee United State of America

Engine Break In

Look under the posting listed as "information" and go out to that site. I haven't read the article but I did notice an article that seems to deal specifically with "engine break-in".

Good luck :-X12

Dec 21, 2001 | 02:22 PM

brown 4x4

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From: Nebraska

Engine Break In

When I replaced the 300 in my truck, I was getting around 10 mpg for the first thousand or so miles, then it slowly creeped up to about 15 after it got broke in. Now I'm down to 14, guess my foot's gotten heavier

Dec 21, 2001 | 09:09 PM

JBronco

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From: Loveland, CO.

Engine Break In

An engine is broken in at 4,000 miles.

Dec 22, 2001 | 11:46 AM

restorit

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Joined: Jul 2001

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From: Bismarck, ND

Engine Break In

As far as the "why" of mileage increasing after break-in, my understanding of the matter is this: A new engine, freshly assembled, is "tight" and has some other characteristics - the rings haven't seated, the bearings haven't worn/matched themselves to their respective surfaces, etc. After the 4000 miles or so of break-in, internal and valvetrain friction is reduced from the individual moving parts having worn into the bearings enough to settle in, the rings have seated, and all of this results in the engine not having to work as hard which translates into better throttle response, more horsepower, and better gas mileage. You might also notice that an engine may run hotter in the first several hours of operation after a rebuild which is, again, due to the initial friction as everything works itself into place. I don't build engines for a living, so someone may disagree and be able to add to this. This is just the explanation I've come to understand having experienced the same from a number of engine changeouts.

Dec 23, 2001 | 10:47 AM

georgedavila

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From: Nevada

Engine Break In

JBronco is correct, your engine is broken in. Ring seating is dependent on cylinder wall honing and they seat or they don't seat. Bearing tolerances shouldn't change from initial values and your cam/timing is installed correctly or not installed correctly.

All performance engine manufacturers suggest taking it easy for the first 500 miles primarily to ensure that nothing is loose.

Any heating problems of newly rebuilt engines can normally be attributed to improper ignition timing. Same principle goes with gas mileage. After the excitement of getting it running, many people neglect going through the procedure of a major tune-up. That should include retorqueing head and intake/exhaust manifold bolts, new or rebuilt carb, setting the timing, checking/replacing ignition wires and replacement of all rubber/plastic vacuum lines.