As some here might know the 3.5 liter Ecoboost engine has some problems such as dilution or shearing the stock 5W30 Semi Synthetic down to 5W20. It has things like cold start rattle and a list of different things. Another key thing is the engine seemingly running too hot sometimes over 220 degrees F! I just dont believe the Motorcraft 5W30 Semi Synthetic is appropriate for this monster. So I looked around on the internet to find other turbo guys facing similar problems and were successfully using 5W40 HDEO most notably Rotella T6. I took note but I wanted to be cautious and didnt use T6 because its not rated for gas engines. So I turned to Mobil 1 Turbo Diesel Truck 5W40 and Mobil Delvac 1 5W40 ESP. I had great results. The engine seemed to run a little cooler with both, ran smoother and the Blackstone lab reports came back with superior results and praise from the Blackstone people. However I wanted to give Chevron Delo 5W40 CK4 a shot. The Delo is about 20% thicker and is API SN Plus and not just API SN like the Mobil variety. Chevron assures us its truly mixed fleet and will work in whatever you pour it into. Gives some of us more assurance that its good to pour into the crank unlike Rotella T6 where where when you email Shell they give you a resounding No for gas engine use. So far the engine is the quietest its been and smooth. Temperature control is superior and I can easily cruise around under 200 degrees F. When I jump on it there isnt the temperature spikes Ive seen with the 5W30 where quite suddenly Im pushing 220+. Its been a lot steadier. In the future I plan on testing the oil through Blackstone to determine which is the better oil...Delvac or Delo.