I've never bothered with having my
oil tested, I just change it and always cut open the
oil filter and inspect.......
A buddy that just recently retired from offshore work (mechanic) would send in a sample of
oil from his daily driver (70 something Ranchero 351-W) when they sent in oil samples from the engines on the offshore rig, he found he could run 15,000 miles between needed oil changes and he did........
On my own cars/truck as well as my company car, I change the oil/filter every 4,000 miles, so far,my company car has "only" 348,650 miles on it, just had to replace the valve cover gasket this year!!!!
they don't make em like they used to!!!!
David