After 40 years I came to the conclusion that 3K changes were a total waste of money since the oil coming out the gas engine was not much different than what was going in. I have run Castrol GTX for decades and got 300K out of a 1979 LTD Wagon, never changed based on miles, just when I felt it was time.
Today I get oil samples tested before changing oil, if it can go another 6K miles, then thats when I change it. No sense wasting resources. My 2019 F-450 tells me to change the oil at 11K miles now, I sample at 6 and it stated good to go, so will see what this last sample says. I found I only need to change the oil in the truck once a year. Some may think it would be cheaper to just change the oil instead of paying for the sample, but it gives me a lot more information than just oil quality, it gives me wear indicators. So far it is wearing very well.
I have a 2014 Flex Ecoboost with 182K miles on it, still going strong, no oil leaks, but the timing chain is approaching EOL as usual, they only last about 180K miles before they start clacking on startup. Only thing the Flex needed was an injector at 60K, engine is all original and has power to spare, Damned good Engine that 3.5 Ecoboost is. On that one I change about every 7K miles, and so far no fuel dilution, but then again I don't drive it in the city, nor the truck, all highway miles. City driving, different story. My wife has a 2015 Focus that is on its third clutch, but the engine runs great and has over 170K on it as well. That damned dual clutch transmission eats clutches, but only the odd clutch wears out, the even disk is still like new. It has that automanualatic transmission.
Whats funny is I change the oil on the F-450 and have just enough oil left over to do the oil change on the B2410. T6 5W40 is what I use and have always used Rotella in my Diesels, never had any issues with it. For the gas engines,I just use what ever synthetic is on sale, last one was Pennzoil.
