Should I be worried about cheap oil change?

FlashBazbo

Sorry, but for the INITIAL oil change, it can definitely harm an engine to change the oil too soon. After an engine has run in on its original oil, which under normal conditions takes more than 1K, THEN there's no such thing as too early (except for the money wasting thing). An engine needs a little time run on less-than-brand-new oil to get everything sealing right and working together smoothly. (Think of it as a final machining/honing operation.) If you don't give it time to do this, you'll see high oil consumption down the road.

[At the other extreme, although I would never come close to risking this in my vehicle -- scientific testing has shown that modern oils in normally-stressed engines (probably not your Z!) are fully capable of providing "new oil" performance beyond 15,000 to 20,000 miles, depending on engine load. I'm a 3K oil changer myself -- and probably always will be -- but I know I'm wasting a huge amount of money at that. My wife's car has an oil quality sensor that tells you when it's time to change the oil. Her second oil change came about 22,500 miles after the first! I've heard that a lot of Hondas using oil quality sensors go over 20,000 routinely between oil changes with no problems.]