Every 3K on all the cars. Even at that mileage, you can smell the build-up of fuel that has slipped past the rings. Not a strong gasoline smell, but there nonetheless.
This last oil change on the Suburban I opted to go with the Castrol Syntec Blend. We'll see how the semi-syn oil does on the 7.4L at 120K miles. Had no leaks before the switch, and at almost 1K since, no leaks showing. In a few changes I might opt for fully synthetic.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.