Discuss. Example-if an engine uses a quart of oil every 3000 miles, and the sump capacity is ~3.75 quarts, can you get away with a longer OCI, considering that you're introducing a fresh quart every 3K? This is my current situation with my Corolla. I'm going to send the oil out after 15K (Mobil 1 extended performance). Will report back with the results.