Manufacturer recommendations vary widely. Some Subaru models recommend 6,000 miles. Some Toyota Hybrids recommend 10,000 miles. Diesel intervals depend on duty cycle. The honest answer is, it depends.
Driving severity
Short trips (under 10 miles) put more stress on oil than highway driving because the engine never reaches optimal operating temperature. Boulder commuters with mostly short trips need more frequent oil changes than long-distance highway drivers.
Altitude
Higher altitude means thinner air, which means engines run hotter on average. Synthetic oil handles this better than conventional. Boulder's elevation is enough to matter.
Towing and load
If you tow trailers, haul gear, or carry heavy loads, your oil works harder. Diesel pickups doing fleet duty or work-truck duty need shorter intervals than the same truck doing daily commute work.
Ask us. We will look at your driving, your vehicle, and your maintenance history, and tell you what we actually recommend, not what the dashboard sticker says or what your last shop pulled out of thin air.