Oil turning dark brown to black
 

We recently lost our dealership who did the oil on my parents 2002 Caravan which currently has 127,790 miles. Since they went under, I did the oil change one time using Valvoline conventional motor oil and an STP filter. After 2800 miles I noticed it was turning dark than it should, so I had the Ford dealer take care of it. Now after a little over 1K its dark brown coming close to black. Any ideas what is wrong with this thing.

They always used conventional motor oil, I know that for a fact. The oil never looked like this before after the usual 3K miles. The enigne still runs like normal, and there are no signs of the engine running rougher, loss of power, or lower fuel economy. The check engine light and oil light have not come on yet. The only thing I know that has changed is it is using a different brand of oil, and we are using 5W-30 instead of 10W-30 which the manual says is acceptable on the 3.3L V6. We have gone back and forth between those two depending on the season so I know this isn't the first time we've run 5W-30 in it. Any ideas of what might be wrong and how to fix it before anything big goes wrong?

Oil turnning dark or black is normal. even after the oil been changed.

I've never noticed it turning dark or black before this or at least this soon. Our other car that is about due for an oil change isn't that dark. Are you positive?

I'am sure. Diesel engine turn black after the engine has been running for five mins.