Purchased a 2006 Escape V6 36000 mi. 2 months ago. Driven 15 miles each way for work on country roads 55 mph every day. Driven very easy in SE Wisconsin. I was an uninformed shade tree mechanic before finding this excellent site. I thought all brands were created fairly equal. Anyway, purchased a case of Citgo 5W-20 semi-syn before finding this site. Plan on doing a 4k OCI and sending in a sample. Previous owner used Motorcraft 5W-20 semi-syn which I now know is an excellent choice. My question is can I confidently go 5k on the Citgo? Tried searching for an analysis but no luck. After the Citgo is gone, I'm switching to the MC. Or should I do a 4k OA just to see how the oil and engine are performing?