I've read a few posts that refer to the engine waking up after the engine is broken in. do you get better mpg and power? is it a pretty sudden change? what kind of milage does it take to break in the engine?

 

With my engine, it wasn't like a sudden on/off situation... after about 2-3K miles (around the same time I installed my Airaid CAI, when I was actively paying attention to see if the CAI gave any improvement), I noticed increased throttle response and better fuel economy than when the JK was brand new. Again, it was gradual, not sudden.

 

Same for me, a few thousand miles and gradual change.

 

X3. .......

 

Mine is an auto and had a big change after 4000k and now I'm at 9500K and it runs so so much better.. It seems to let go after it breaks in.

 

I'm with airric00 on this, I'm at 8k miles and in the last 2-3k miles I've noticed a very large improvement.

I run 35's with the auto and 4:10s and I don't consider my Jeep "slow" any more.

 

I will have my brand new JK 2 door Rubi 3.8 in the next day or so. My question is how to run it in out of the box. Should i drive it like I stole it at high rpms or should I drive like Miss Daisy at low rpms when new?
What do you guys think?

 

I've had the same experience as some others here. Mine kinda woke up when it got around 2300-2500 miles on it. I have no doubt that the engine was broken in well before that. Modern piston ring technology has just about done away with a break in period. Engines nowadays are all but broken in the first time they warm up. This is due to both modern parts technology and modern machining processes. Still though, something has to happen right around the mileage everyone is concurrent on, and I'd love to know what it is. Perhaps it takes that long for the drive to imprint on the computer with the drive by wire technology. Since I've never been one to give a vehicle hell, I just drive it like I intend to right off the bat.

 

This is what ***I*** have always done with new vehicles (YMMV--literally!):

1. First 50 miles, stay below 55-60 mph. Use varying speeds. Don't get on the interstate and set the cruise at 75 for the 50 mile trip home from the dealer. This is for the tires, BTW.

2. First 500 miles, like you're Morgan Freeman. Higher speeds are fine, but don't press for redline, and don't expect top performance quite yet.

3. Change engine oil at 500 miles. In the past I've always found this to be the dirtiest, blackest, grungiest looking oil I'd ever change. On the JK, for the first time ever (I'm 58 years old and have owned more than a few new vehicles), the oil came out looking like new. But, I'd still do it anyway. This ensures that any detritus left over from the manufacturing process is flushed from the engine. Okay to drive at higher rev's, but I'd still be a little bit reserved.

4. Next oil change at 3000 miles. You'll likely notice a significant change in performance. The engine is well-broken in; it ain't gonna get no better (without mod's). Drive it like you stole it (if that's your style).

 

What I was referring to was the honing process. Years ago it was not done with a torque plate installed to duplicate the cylinder head being installed. Now it is. I've been to ALL three of the big three plants closest to me in the last ten years through dealerships and they all use torqe plates now. That in itself almost eliminates piston ring break in. Almost, but not quite. I've no doubt though, that they do even all that as cheaply as possible.