Originally Posted by Salzig
A bit OT.
I'm always surpised by the oil changes interval you are reporting.
Here in Europe (at least in Italy) for new cars, tightest change intervals are 15000km (~9500mi), normal intervals are 25000km (15500mi). Diesel or gasoline doesn't count.
Last service on my car, a Suzuki SX4 with 15000km, the dealer didn't even changed the oil, as the oil pollution meter on the dash said it would have lasted another ~20000km.
Once I went synthetic back in the 80's I changed the oil in my cars about every 15K miles. And I ran the crap out of them, 2 liter turbos, that I had running with water/alcohol injection so I could run close to 28psi boost, putting down in the neighborhood of 300 hp without detonation. Later years they also pulled my 6x10 enclosed trailer with 3 motorcycles at times, would run hours at 5-7 lbs boost, that is aircraft duty!
And all three of them were retired at close to 300K miles, not due to mechanical issues, but rust as I live 20 miles from one of the worlds largest salt mines and they spread salt inches thick when it gets slippery.