OK to use 5W-40 Valvoline Full Synthetic all year in Wisconsin?

Short story; I've always used fossil Valvoline 15W-40 in my 5.9L diesel. In 6/2018 they changed oil @ 299K using Valvoline Premium Blue Extreme 5W40 Motor Oil by mistake, whew what a change in $$. I noticed a significant positive change in starting in <zero weather & kinda like that!

I'm now at 309K prepping for trip South & finding some to take along for backup. I see on Valvoline's site that this is NOT listed for use in my light truck engine, only for the big rigs!?

We're staying in FL for next 2 months, avg. high temps 70-90 deg., then returning to SE Wisconsin. May I presume that:
1-short (2 month) towing & visiting in hot climates are no problem?
2-continued use (10 months) in SE Wis. weather is also, no problem?

This full synthetic is very expen$ive, buuut its performance this Winter was most desirable, and changing it annually (22K avg. miles) is an attractive option.

Does this still sound reasonable or should I stay with 2+ fossil oil changes annually to "flush" the carbon or stay with Full Syn. all year & change the filter after 6 months?

Pls., is there a downside with this scheme and how bad is it?

Thanks much,

Wally J.

 

What most people fail to understand when talking about 5w-40 full syn VS 15w-40 dino oil is.....

They both have the same viscosity at operating temp. The difference is the W (Winter) grade, which is what viscosity your oil will be when your truck sits outside all night in the cold. One will have the 5 weight and the other 15 weight. So on cold starts you can see the improvement.

Also the 5w-40 has the obvious added benefits of a full syn oil. You can run 5w-40 all year if you wish, just very costly to do so.

 

my 03 has 455k has been on 5w-40 mobil 1 for 424k and i live in florida

 

If you don't mind sharing, 2 questions:
1-how much towing?
2-oil chng schedule?
Thanks for responding.

 

most of the miles are towing,oil change every 10k

 

Thanks friend.

 

I run Valveoline 5-40 syn all year. And We do see temps as high as Florida etc. and it's fine. As already mentioned the operating viscosity is the same for both, just better cold starts and the syn. tends to stick to surfaces better and thus lowers the "dry" start issues for the moving parts till the oil is flowing. The Valveoline premium blue you mentioned is what all of our Cummins are shipped from the factory with and is what I use.