It has been stated on this site that some semi-synthetics are as little as 10% synthetic. Wouldn't you be better off mixing 3 quarts Mobil Drive Clean and 1 1/2 quarts of Mobil 1 (4.5 qt. capacity )so that you know that you have a 33.3% synthetic oil. If this is done what would be a safe OCI? If dino is good for 3K and synthetic is good for 7.5K + would this homebrew be good for 4.5 to 5K. Any thoughts? I assume you should stick to the same brand when mixing.