Originally Posted by sprintertech
no your right.....i would not use royal purple either.....i use mobil 1
I also use M1 synthetic and the inside of my 3.7 is sludge free at 90k miles. I change it at every 5k along with the filter. Right now, I'm trying out the extended life formula that claims 15k between changes but I plan to change it at 10k. Around 5k, I'll pull a valve cover and check for any signs of trouble.