With how advance technology has become and how manufacturing has changed monumentally over time, I think the factory break in is all that's needed. The day and age of keep it under 40mph for the first 500miles is over. Infact, race teams will build an engine the night before a race and have it reving 5-6K all day long.

The Mileage Constraint before towing is more than likely a legal matter added or just a grandfathered clause. I'm sure every auto enthusiast who's a purchased a new car had more fun with it the first week they bought it than they did months down the road.

 

theories on engine break in have changed greatly over time, no doubt.

however, the mileage constraint on towing i belive still follows current break-in theories.

Ford recommends not towing for 1000mi, and within the first 500mi of towing, you should not exceed 70mph with no full throttle starts. (Pg. 275 of the 2011 owner's manual, 3rd printing)

that is a very strong and specific recommendation to simply be "a carry-over" from the days of old. .... i would follow it, as i belive it has everything in the world to do with breaking in the ring and pinion.

 

Substitute the word "recommendation" with "best practice". Ford is giving us free advice about best practice based on their wealth of experience. (Well, I guess it wasn't free since we all bought a truck ) Since I'm not a drivetrain designer I'll just default to following the best practices that the designers thought were important for me to know. Seems like a better alternative then following the advice of a layperson on the internet?

 

It really can go both ways: Ford is either covering themselves on any engine related legal matters or it is truely beneficial to properly seating the rings on the pistons.

With so many different opinions, which do you really believe? I can only speak from experience, and I have built a few engines that had to be taken apart again within early mileage and two went through differentiating break in techniques per the owners request.

When I took the engine that was broken in like ford recommends, two pistons had ring failure. Car was driven under 60 on the highway, never revved past 3500 RPM, never towed a single thing. In between the Top & Oil ring there was a bit of blow-by. Now it wasn't noticeable upon driving but it could have been a bigger issue down the road with compression.

The second engine was my own and broke it in by running it at idle till it was up to temp. Turned the engine off and let it cool for 2 hours. Came back, warmed the engine up at idle and them held the RPMs at 1200 for 5 mins then turned the engine off. Came back after a drink and then started and held the RPMs at 2000-2500 for another 5 mins. Let it cool off, then started it and held the RPMs at 3000-3500 for about a minute. I did this at 11-12 at night so afterwards I was beat from plugging everything up and just went to bed and let the engine cool off for the night. The following morning I took the car to work and drove it normally and while going home I took it through the revs in between shifts. 20K miles later, I took apart the engine to swap cams, pistons and send the block to get bored out and when I compared the look of both pistons, mine were exceptionally clean. Little to no blow by at all between rings and the tops of the pistons were really clean(no excess carbon build up at all).

Now I must say, I didn't tow anything, but I put some decent load on the engine winding it out on the highway for the 20K miles since rebuild.

Essentially, it comes down to preference of how you want to break your engine in. I more than convinced the way I went about it was proper simply from disassembling the engine and see it all for myself. I'm not saying Ford's technique is wrong, though I found a way that does not inconvenience me from driving spiritedly.

 

the only thing that the owners guide says about engine break in is that an extensive break in is not required. Only that you should not drive continuously at the same speed for the first 1000 miles. and then not to tow for the first 1000 miles.

i'm quite sure that the engines are broken in before the customer ever gets them, most likely before they ever leave the assembly line.

i think the rest of it is for the moving parts that cannot be broken in any other way than driving, transmission and axle componets mostly.

 

I think this is really more the case than anything else.

I had a mechanic who built race cars for a fellow install a Jasper short block in my '88 F-150. The truck had 101K on the clock when the OE engine failed. After assembling all the pieces and delivering it back to me, I asked him for the proper break-in procedure. He said to simply break it in the way I intended to drive it.

So, for the remainder of the time that I owned that truck, 14 years and 120K miles later, I ran the **** out of it. When I sold the truck with 221K on the clock and 120K on the engine, she was running like she was new.

The key was timely proper maintenance.

 

I can say i didnt do the factory recommended break in on my 2011 yamaha four stroke outboard and its tight and runs like a champ. They have an issue with making oil. Gas in the oil from blow by. I ran the crap out of it after reading a bunch of fourms and seeing what others were doing. It worked for me engine wise on that one. I just have a hard time believing that a rear end needs broken in maybe it does but so far my truck is a ok with the way it drives and feels after towing before the recommended 1000 miles.