I wouldn't Mix the two together. But one article from the internet which I agree with is, If you do use semi-synthetic engine oil instead of fully synthetic oil then it is unlikely to cause any drastic or immediate problems. However semi-synthetic oil will not offer your engine the same levels of protection to your engine that fully synthetic oil does and may result in reduced engine performance.
I can't imagine that mixing them would matter at all. After all a synthetic blend is basically mixing synthetic with dino ahead of time. It would just alter the blend percentage. Also, I don't see how it would reduce your engine performance in any noticeable way as synthetic blend is what Ford specifies for the engine. At least that's what my owners manual calls for. In fact, the way I read it the optional oil is a full synthetic and the OM says nothing about any special procedures or precautions when using either.
As long as they are not mixed, filling oil with Semi Synthetic won't hurt the engine. It will still meet the engine spec for type of oil I am sure. When full synthetic is back, use it at your next oil change. Good luck
There is no issue.
Been using 5W-20 and 5W-30 Motorcraft synthetic blends for over 10 years in every vehicle I own. Oil wear analysis always almost puts them at full synthetic equivalent as well. Those oils have no problem going 5000-7000 miles between change intervals as well.
Jeez, with that kind of mileage you could use olive oil and be fine. Seriously, the blend will be just fine.
