Hello All, Long time lurker here, and couldn't find any related posts, so I figured it was time to sign up and join the community. I hope I'm posting this in the right place! Here is the run down: I just pulled the trigger on a new 2017 f150 XLT FX4 5.0L. I broke the truck in as recommended, took it on a 1200 mile road trip, have been commuting in it daily. (~45 mile round trip) I have about 3500 miles on it, it has been running great. I was told by a friend that I should go ahead and get factory oil out of the truck and change filter. I figured it couldn't hurt so I bought a new OEM motorcraft filter and decided on Penzoil Platinum Full Synthetic 5w20 as recommended by Ford/ the community. I went to buy some oil at w-mart but all they had left was one 5Qt of the regular full synth. I looked up and they had plenty of the PP High Mileage 5Qt. From what I have read on this forum this just means it has a better "detergent package." So I went ahead and pulled the trigger on buying one of each, 5Qt PP full synth, 5Qt PP full synth HM. I wouldnt think there would be a problem mixing the two, so I did.. the truck has been running great. It seems like every fill up I am getting 0.1MPG better mileage. I attribute this to further engine break in, not the oil...and I really could care less about mileage anyway.. just and observation. Are there any negative effect by mixing the two? the truck holds ~8L of oil, I use the full 5Qt of the PP Full Synth, and about 3Qt of the PP FS HM. Maybe I am just driving myself crazy? I'd love to hear what the community has to say. Thanks, Taylor p.s. Please forgive any spelling and grammar mistakes... I typed this rather quickly.