What weight oil to run?

[sugelle]

New to diesels and trying to figure out what weight oil I should run in my 2010 6.4L F350. I just bought it this month and it only had 10,200 miles on it so still really new. I read manual and it appears to call for 15W40 but also lists 2 other lighter weights. I live in Midwest (St Louis area) and we have hot summers (mid to upper 90's and humid) and cold (20F-35F) to sometimes very cold winters (temps in low teens). I only tow bass boat and cargo trailers/utility....nothing heavy. I also wonder if the heavier 15W40 comes in synthetic?

[montana6.0]

Not sure about synthetic 15/40 never heard of it. But i run it in the summer then switch to a synthetic 5/40 for winter. I run rotella t its been great for me and many others on here.

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[jesilvas]

15W40 would be fine, but 5W40 syn is best.

[superduty6.4]

I run 5w40 year round. I've done so for about 115,000kms.

[rt_hawk]

15/40 or 5/40 syn or Dino is ok...change it every 5k or down to 3k if you plan on leaving the dpf on and do a lot of stop and go driving or short trips...

[rt_hawk]

Amsoil makes a synthetic CJ-4 15w40 btw...I love synthetic schaeffers 9000 5w40 myself, I buy it for 6.50 a quart and my UOA's are spot on, it's a great quality package for the money. Amsoil is like 10 a quart around me...plus my UOA's always had high copper until I switched to schaeffers, then they dropped and stayed low....

[Doss]

I wouldn't bother with synthetic; but that's just my opinion. Why don't you just run whatever weight you need for the season?

If you're going year round, 15W40 should be fine unless you're really getting continuous cold days (below 20°).

After my recent Blackstone Lab test, it says I can stretch out the Motorcraft 15W40 to 7500 miles since no signs were out of the ordinary (and this oil has been run pretty much since day 1 out of 86,000 miles).

[rt_hawk]

Doss is right, syn is useful for cold climates or when extended oil change intervals will end up saving you money, but dino oil is just as good as syn in terms of protection. And MC oil has a very good additive package. In St. Louis your good with 15w40 and if it gets real cold just plug it in...

[sugelle]

Personally I dont like having to remember to switch weights for seasons. The manual shows 5W40 as "year round" based on ambient temperature chart but my dealer says they put 15W40 Motorcraft in all the 6.4L they service. I just wanna be sure I dont make mistake since this is my first diesel. I dont mind paying the $$$ for synthetic...I religiously ran Mobil 1 in all my gasoline trucks.

[blackcloud2k]

I am like alot of guys 15-40 dino Rotella for the summer, and 5-40 syn Mobile for the winters. It gets in the negatives ALOT around me so its nice to have the lighter weight in the winter. Running syn year around if your not going to extend your change intervals is very costly, and you wont benefit from it. Its just not economical in my eyes. I change my oil every 5k miles no matter what I run. If I were you just put 15-40 in it year around and you will be fine. Either Rotella, motorcraft, or mobil will be your best bets, and all 3 of them are found just about anywhere.