I have 120,000 miles on my '99 3.9L. I've always used 10w30 convention oil but am considering switching to synthetic (mobile 1) andNAPA gold filterat the next oil change. I haveno oil leaks or consumption. Any concerns with doing this since the engine has quite a few miles on it?

 

youll be fine

 

should be fine if you wanna play on the safe side use a blend for like two or three oil changes then swith to a full synthetic but i switched mine over at 90,000 with no worrys or leaks

 

make sure you get all the old oil out,
when i switched over, i put three quarts in, ran the engine for about five minutes, then drained it again.
it's time for me to change it and the trucks never run better for me

 

no problems