I have a 03 Toyota Tacoma V6 and I didn't do the first oil change until 4k miles. I was just going to follow the scheduled maintenance which said, first oil change at 7500 because I didn't know any better. luckily I changed it before then, because when I drained the original oil it was very black. My question is do you think I have done any damage to the engine? If so are there any recomendations to minimize it. Since then I have changed the oil at 6k and now I'm at 8k. I used Valvoline 5w30 for the first 2 changes, on my next change I plan on using either Chevron 5w30 or M1 5w30.