I have a 2001 Dodge Durango with the 4.7 engine that I purchased new in 2001 and it presently has 199,000 miles on it with nothing ever being done to the engine. I have changed the oil every 3000-4000 miles with 5W-20 conventional oil per the service manual until around 150,000 miles when I switched to 10W-30 conventional oil. My question is this; why does the engine use the first quart of oil after 1200-1300 miles and it only takes 500-700 miles to use the second quart? The engine does not smoke or leak any oil.

Have you put a pcv valve in it? If not, do that and it might be worth getting it from mopar, and be sure the housing-seals are good where it installs. It's a cheap thing to try.

Yes, and it makes no difference. This oil consumption phenomena has been going on for the past 100,000 miles.

One possible answer is that with use the oil's viscosity index additives are shearing down, resulting in oil that has less than stock viscosity at operating temperatures.

This happens a lot more with petroleum oils as they require much more of the VI improver to flatten the viscosity x temperature curve.

A good synthetic might help this issue.

A way to check would be an oil test.

R.

"One possible answer is that with use the oil's viscosity index additives are shearing down, resulting in oil that has less than stock viscosity at operating temperatures."

I was thinking something like this could be the reason.

By the way I have tried synthetic oil with the same results as with conventional oil.

My 02 quad cab with 4.7 called for 10w30 oil. After 9000 miles I switched to 15w40.Ran it that way until I traded it in with 205K on it. It was just then starting to use about a quart between oil changes... 4-5000 miles.