The 5W20 oil is too thin for the higher HP output of the ecoboost twin turbo engine.
The bearing loads are much higher than the N/A engine has to deal with. So Ford increased the oil to 5w30 to handle the higher bearing loads.
Temp is on the right path but has nothing to do with it as both synthetic 5w20 and 5w30
have the same high temp limits. However synthetic oil has a higher temp limit than does dino oil. That is why they recomend using synthetic oil. The turbos when run hard glow red and introduce a lot of heat into the oil and water jacket. If the oil can not handle the heat it breaks down cokes up and looses its lubricating ability. That then leads to engine damage. So by all means people use 5w30 synthetic oil in the twin turbo version.
By the way not all synthetic 5w30 oils have the same max temp limits some are higher than others. As a rough example Dino oils max temp is around 450F while synthetics are around 620F. Now you can see why they recommend synthetic oil. But some are as high as 650F with additives. Obviously you do not need the best unless you are pushing your engine higher than factory rated power. Then the best you can get is good insurance policy.
