I have two toyota trucks. I'm the original onwer of both. One is an 84 4x4 22r 5sp reg cab and the other is an 2001 tacoma 2.7l 4cyl 5sp reg cab 4x4. the 84 has 211 thousand miles, 90% with havoline 30W and fram filters. no engine repairs at all. the head has never been off. I'm not even great at maint. OCI's vary from 3k to 7k miles. I run mobil 1 oil 5 w 30 and mobil oil filters in the tacoma. Why should I run syn?