I brought my E350 6.0 to a Ford diesel mechanic and he inspected my Rosella T6 5w40 and said I need 14w40 because that is Ford's spec.

I see other folks using 5w40. Should I be concerned? I bought 6 gallons of it on sale at Walmart. Easy to return.

Thanks

 

Do not let him touch your truck if he's that simplistic. The 5W40 syn. Is an upgrade to the 15W40. I will say that you may or may not need it but that is an opinion. The syn. Oil is good in extremely cold to extremely hot environments. I live in S. Ca. And ran it all year long in my 6.0 and now my 6.7. The syn. Has less of a tendency to coke in extremely hot areas such as your turbo and has been known to help with striction. That's my stand along with many others here.

 

I got tired of everybody saying: run only 15w 40, or run only 5w 40, so I said screw it and just run a blend of both!

I'm just kidding about doing the blend because of folk's opinions -- I've been blending my own oils for years (from off the shelf oil). I chose the Delo oils and run 2 gallons of the 5w 40 syn and the rest 15w 40 delo 400 -- figure it's about a 9w 40

Truck has zero romp on cold start, runs smooth and I just happen to like the way the two add packs of these oils match up...

But that is me and most here know I'm a little tweaked, sometimes a lot tweaked!