engine break in
Legend
Joined: Nov 2014
Posts: 8,098
Likes: 318
That sucks about loosing yours to cancer...luckily we don't have that much of a problem with rust in Northern Nevada...and don't get me wrong I'm not giving up Durangos...I have 2 more (technically 3 but #3 is a parts carcass and 2wd) Both of my Durangos have the 4.7l engines ones a '00 and other is a '01...both are currently down the '00 had a timing chain passenger side failure an the '01 dropped #8 valve seat. So they will be back on the road as soon as the 5.9 is gone 
Grand Champion
Joined: May 2019
Posts: 5,146
Likes: 721
From: S.W. Indiana
It's a rather old thread but I'll answer this. When an engine is first built, or rebuilt, the cylinders have been bored or at least honed. This makes them extremely smooth if done right. A good honing will leave a slight cross hatch pattern on the cylinder walls. You now add a piston with several layers of piston rings on it. They are designed to flex a little as they move up and down. There is also one or two oil control rings at the top of the piston. As the piston slides up and down, a little oil leaks past before the rings seat into the bore. Once they seat, very little oil gets past them.
Engines designed to use synthetic like a BMW or Porsche are "run in" before being put in the vehicle. Synthetic oil is so slick the rings can't scuff in to seal so break in oil is used. It is then changed to synthetic when it goes into the car. It's been a while since I've doe a total rebuild but it was a Chrysler 400 big block. After boring it over, it was a 406. It used a quart of oil in the first 60 miles. After that with oil changes every 3000 miles, it didn't use enough to notice for the next 25,000 miles. I sold it to friend and it's never used any oil on him either. So, get a good break in perio and you have a nice tight engine.