Turbos should have their oil service done every 3,750 miles. If you are under severe driving conditions, such as using high octane fuels or accelerating hard, your turbos may need to be replaced more frequently. You should replace them either 7,500-15,000 miles, or 30,000 miles. If your turbos are showing signs of wear and tear, such as excessive noise or starting issues, you might need to replace them sooner.