interesting Q that I was trying to ask myself a few weeks ago when i did a change on my focus.
I attempted to look at all the pro's and cons of each. In the end I went to my local ford dealers and asked them. The guy behind the parts counter was really helpful and told me that by factory stock my focus tdci uses semi-synthetic 5-w30 formula-E which conforms to specification WSS-M2C913-B. He also said I could purchase this from ford direct if I wished. (at this point I was expecting a very high price tag) however it was only £25.99 for 5 litres, I didnt think that was a bad price for ford oil and liked the idea of keeping the same oil in the car as it gets when ford services it
they also sold me the official filter for £8
the guy behind the counter said using fully synthetic over part-synth had virtually no advantages for the type of general driving I do (as im not really putting the engine under a huge amount of strain or anything, so I thought why bother paying more and changing?
If ford use part-synth I guess thats what the engine was designed for
however any 5W-30 oil which conforms to WSS-M2C913-B should be fine for my engine, not sure if the specification is the same for a petrol? it says the specification needed in the handbook near the back pages
hope this helps
The ford M2C-913B spec replaced the original M2C-913A spec and is for both Ford petrol and diesels (with a few exceptions such as the new ford focus RS and the VW engined diesel fords. Oh and some of the new euro iv spec diesels).
Ford dont recommend semi or full synthetic, just a spec such as the Ford M2C-913B spec, and a viscosity 5w-30. For warranty purposes as long as the oil meets this spec what it is made from (semi or full) is down to the owner.
If you look here you will see a mix of semi and full synthetic 5w-30's that all meet the ford spec http://www.opieoils....-m2c-913-b.aspx