I run the T6 ROTELLA in South Texas (where some years we don't have a freeze . . but use the air-conditioner to cool the cab for at least nine months). I was using 15W-40 Rotella with no issue, but thought I'd change. The engine turns over noticeably easier year round with the 5W-40.

FLEETGUARD Stratapore LF-16035

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Nitrous,
I am an Amsoil Dealer so I guess I would be a little biased towards using Amsoil products.

Amsoil recommends 15W-40 for -18C and higher while 5W-40 is recommended for "all temperatures". 5W-40 obviously has a broader temperature range. 5W-40 offers better protection on cold start ups and also gives you the same protection that a 15W-40 would once the engine reaches normal operating temperature.

I know that Amsoil is more expensive than other oils but I believe it is well worth the price. Especially considering the extended drain interval.

Anyway, do what works for you but I think you would be happier with a 5W-40 over a 15W-40.

 

I run Amsoil 5W-40 in my 2005 Dodge/Cummins and love it. I am in AZ but I am in the cold part of AZ. We have cold winters (not as cold as some of you guys) but we also have hot summers. So this gives me the best protection year round.

 

Well did the change myself with 5w40. Not too hard other than getting the new filter back up in there. Had it filled to the top of safe mark now after driving 50 miles checked it and it is over the safe mark! Im going to drain a little but wondering if this could of done damage ?
Thanks

 

I run Amsoil 15w40 HD Diesel and Marine in mine.. we don't get THAT cold, but do get to around 15* F...
Works great.