Originally Posted by A_Spruce
I've always used conventional oil and done OCIs at 3500 miles. I've now changed to Mobil One synth in a new-to-me '03 Suburban, manual says 3500 miles, OLM has yet to come on at nearly 4K miles, mechanic suggested 5k OCIs, and the fine folks here are suggesting 7500+ miles.
I have not yet decided just how long I'll go between OCIs over the long run. I will be doing one in the next few days due to a leaking oil filter and not knowing when I'll have the opportunity to get to the next OCI, and I'd rather short change than go too long.
At last oil check, the level is down slightly, but well in the healthy range, I blame the filter leak only, I don't believe there is any consumption (150K on motor), and the color of the oil is getting dark, but it is by no means black, burnt, thick, or sludgy looking.
FWIW, I drive mostly in town miles, lots of idling, AC is almost always on, simply because GM is stupid and can't design an air recirc system that doesn't have the AC running. Yeah, yeah, I know why it's done, but the AC doesn't need to run all the time to accomplish it's purpose.
I think even with your tougher than usual drive/commuting habits, a synthetic oil should do ok with a 5k mile OCI, as long as you check your oil level and make sure it's topped up. That engine is not direct injected and should handle 5,000 mile intervals easily.