5W-20 or 5W-30 weight oil

[DonC757]

About to change the oil in my 2019 34G V10 Ford. The cap on the oil fill tube has 5W-20 in big yellow letters on it. The Ford owners manual has a diagram that says to use 5W-30 for summer temperatures. Just above the diagram it says use 0W-30. My RV will live in Florida except for summer trips up north. I think I am going to go with full synthetic 5W-30. My understanding is thinner oil’s flow better when cold and slightly improved fuel efficiency because they flow easier. Thicker oil’s lube better. I figure since our V 10 engine’s work hard for every minute of their life and mine will never see really cold temperatures, I will go with the slightly thicker oil. Any thoughts will be appreciated.

[onewinglo]

I had a excellent discussion with a former maintenance chief for FedEx North America. FedEx serves as a test bed for a wide range of automotive products, including engine oil. First, full synthetic vs Motorcraft synthetic blend (semi-synthetic):
IF full Synthetic would have resulted in a 2 mpg increase OR and extra 20,000 miles to the life of the engine it would have been cost effective. It resulted in neither. So FedEx continued with Motorcraft synthetic blend.
If I remember correctly, he stated my V-10 was designed around 5W20 and the heavier/lighter weights were available for extremes. They didn't bother.
I live in the South and use Motorcraft 5W20. It's on the oil filler cap, easy for me to remember, and in the long run I suspect the old V-10 will perform fine.
Note: The maintenance chief did say they determined full synthetic fluids were cost effective for both transmission and the rear end.

[1955farm]

5w-20 is what is recommended in the newer V10s and is what I use. I do use a full synthetic with a Motorcraft oil filter. If you have doubts why not call your local Ford expert dealer and see what they recommend.

[t18skyguy]

I have a 2017 V10 and it calls for 5-30 wgt on the filler cap.