The 4.7 will take what ever you want to toss at here. I ran everything from Mobil 1 5E30 to Mobil 1 15W50 in it and never had a problem with mine. Some people have started to have problems with oil consumption because of how high up they put the top ring. That was never an issue for mine though. I know for a fact that when that engine was first designed the engineers tested and validated it with 10W30. Then just before they took it to production they decided to reclearance the oil pump gears to provide the same pressure and volume with 5W30 oil. You can easily read that information from ALLPAR along with all kinds of design details and cut aways of the engine etc......I never heard of them reclearancing or issue a new part number for an oil pump specifically clearanced for 5W20.....They definitely did not revalidates the entire drive train as that would cost too much. I am sure they probably just took a few fleet vehicles tried 5W20 in it and looked at UOA and maybe one analytical forensic tear down. That is not really validation. Their H.O, version still does not recommend 5W20 last I checked.
Many 5W30 conventional oils break down to a 5W20 after about 1500 miles and some Synthetic 5W30's where awfully thin to start with like Mobil 1 5W30.
Mow the real question is what do you hope to gain by going to a 5W20? A 5W30 or a 5W20 are going to be so close that in your application you will never ever see a fuel savings not even over a 12 month time frame especialy if you are talking about synthetic oils they are both a 5W's.....A solid 0W30 or 0W40 would save you more in fuel cost's then a 5W20 would when compared tot he gold standard in America of 5W30. If you wanted a premium product that will work great inthat engine I would recomend the following Amsoil HD 5W30, Redline 5W20,5W30,0W40,5W40, Mobil 1 0W30,0W40 and Delvac 5W40,Rottela T 5w40.
If you wanted to save fuel I would try Redline 5W20 as it has a boat load of molly which is a great friction reducing agent next would be Mobil 1 0W40 it shears as you pour it into the engine but it does not seem to effect it's anti-wear performance and helps it's fuel ecconomy especialy upon start up and the first few miles to warm up!!!! I have never been impressed with Amsoils SS 0W30 but I love their HD 5W30!!!
I am partial to 5W40's myself and have never seen a milage improvment even when I went with Mobil 1R 0W30 Racing Oil which is or was really thin! I think most synthetic 5W30's are about the sweet spot for the way the average American drives really and have not seen where 5W20 has been able to do anything that a good 5W30 could not do. If the fuel savings was drastic I could see it but a truck owner is not going to see any difference you have too much parasitic drag going on to even notice the modest improvment.
