You can use either.

However, synthetic would be the better choice because they are superior to mineral oils. Just depends on how much you want to spend.

And don't forget to change the oil filter. The standard Motorcraft is a fine filter so just stick to that one.

 

If you're just running on the street... for the first change, I'd recommend regular oil.... go to synthetic at the 2nd oil change.

(some may differ in their opinon... I went to synth myself @ the first oil change and have had no problems.. but I race the car regularly hence my change so early.)

 

Sorry - I think you misunderstood. Im not changing the oil, I just need to top it up but not sure what type of oil the ford service dept would have used when they did the last service

 

Give em a call and ask. Otherwise just about every oil should be compatible with another oil be it mineral or synthetic.

 

Isn't it a safe assumption they used Motorcraft 5W-20?

 

ford would have used mineral, no question.

 

Yes, but you should STILL change to synthetic once you have the engine "seated", IMHO. I'm a true believer. It does make a difference and in the LONG run it is the lower cost option.