How many miles does the 5.9 take to break in? I have heard that it takes quite a few miles to reach the best milage and power output.

 

it does take a little while for best results, with mpg. drive it now how you are going to drive it normally.

 

I know for myself it was around the 55-65,000km mark where I started to see some better fuel mileage.

 

On both my 01 and 06 I believe they weren't really broken in until around 25K miles. I just drove them the way I always do right from the start and didn't worry about anything special.

 

Towing and driving it hard "drag racing" will break it in sooner. You can tell when it's broken in as there will be no more blow by. It took about 20K for mine.

 

I'm at 15k with my '07 and still have tons of blowby. I'm guessing it will take another 15 to fully break in. My '03 didn't take quite as long, but maybe I worked it harder....

 

I think Cummins recommended about 20K miles before you switched to synthetic for these motors. Probably aligns nicely when they think the average motor should be broken in...

 

Could one of you guys please explain "blow by" to a diesel dummy?

 

If you look under your truck when it idles, smoke will come out of the breather tube under the engine. It is lost combustion gasses that seep past the rings on the pistons. The better broken in the engine is, the less blowby there is. On some pulling videos there's so much blowby it's like another exhaust pipe blowing white smoke on the bottom of the truck. I guess that's what you get at 100lbs+ of boost!

There is a way to measure if it's excessive or not, but it is pretty involved IIRC.

Some trucks, like the Fords, dump this back into the intake. The Cummins vents to the atmosphere.

 

The old CCVs in the Fords. Makes a mess out of everything!!