i use rotella T6 in all of my 4 cyl vehicles (gas) ranging 15-20 years old, very pleased with it, no issues. oil consumption is minimal, engines in good shape, oil starts to turn dark around 2.5K. my question is frequency of engine oil change. currently do filter/oil change between 5-6K and realize the best answer to my question would be to get an oil analysis, but defer to the forum expertise @ this point. I've read 7-10k for synthetic are more the norm. My question is on smaller 4cyl engines, is it advisable to change more frequently than the std 6-8 cyl engines most americans use. other than oil analysis what is your take, am i overkill? thx in advance