10w40 or 5w30 for the winter?

[oil pan 4]

10w is fine. Just don't start it and romp on it. Probably make sure it's fresh oil and not coming up on the end of the oci when it's that time of year where it hits -25c. Burned up 10w oil with several thousand miles on it that's been ran for a few hundred hours can most definitely start to cold flow like a 15w.
Only see problems when it's a 15w oil, around -25c. By problems I mean crushed filters.

 

[kschachn]

The worst issue would be an oil that cannot be pumped.

He-man stories aside it’s better to learn from and take advantage of advancements in oil technology.

 

[0burb8]

Is the 10W-40 you can get for free a HDEO with a API CK-4 Rating?

If the free 10W-40 oil is API CK-4 rating, I would use that year round based on your temperatures from my experience. If the free oil is not a HDEO with API CK-4 rating I would not use it.

The 2003 LB7 Engine was designed to use a HDEO with API CI-4 (current rating CK-4). Factory fill for the 6.6 Duramax Engine since 2001 Model Year has always been 15W-40 with the most current API C?-4 rating)
For cold operation below -18C(0F) 5W-40 is recommended.

I have made many cold starts with the 6.6 Duramax down to -25C(-13F) without switching to the 5W-40 oil. My trucks were stored outside and did not have preheat or battery warmer blankets. Oil analysis never showed abnormal wear metals. Have made a few starts at -30C(-22F) with 15W-40 during the rare cold snaps we would have every 5 or so years. With good battery charge they would crank slow but still start.

PS. I would love free good oil. Enjoy.

Slick

It is indeed an API CK-4 oil. The 5w30 option is also.

 

[Nesterenko]

It is indeed an API CK-4 oil. The 5w30 option is also.

What's the problem, 5w30 is the logical and correct choice especially when winter starts to settle in. Your operating temps probably aren't high enough to warrant a 10w40. Like post #22 said about advancement in oil
technology, go with that.

 

[0burb8]

What's the problem, 5w30 is the logical and correct choice especially when winter starts to settle in. Your operating temps probably aren't high enough to warrant a 10w40. Like post #22 said about advancement in oil
technology, go with that.

The problem was that I didn't have enough knowledge to make the decision. I wanted to have opinions about it and got them, and I thank all for them.

 

[6.7 CTD]

The problem was that I didn't have enough knowledge to make the decision. I wanted to have opinions about it and got them, and I thank all for them.

Run the 40 weight, especially if you tow, it’s a diesel.

 

[Lubener]

I'm about to do an oil change soon on my 2003 Silverado LB7 diesel. It gets occasionally down to -25°c where I live.

I can't decide what to do. I have free access to 5w30 and 10w40 Motul Tekma+ oils. Using 5w30, cold start lubrication is not a problem, but the viscosity is thinner at operating temp.
Using 10w40, cold start lubrication could be a problem, but the viscosity is what the engine calls at operating temp.
It's a small sacrifice both ways.

Please help and point me in the right direction.

I would go for 10w-40 for your diesel.

 

[Slick]

It is indeed an API CK-4 oil. The 5w30 option is also.

I would use the 10W-40 all year. Enjoy the free oil.

Slick

 

[Strumpan_]

I would never pour any 10W-XX oil in my engine, way too thick for our winters

 

[BrianF]

10w30 conventional and semi synthetic have served my 2017 Ram 3500 6.7 just fine since new. Have plenty of cold starts and idle hours in cold Saskatchewan winters. 163,000km and now discernable oil consumption.

I did one 24,000km index with semi synthetic 5w30 but had a little consumption, added a liter at about 17,000km.

I'd run the 30 weight. Your Duramax won't care.

 

[Allaneddie]

I'm about to do an oil change soon on my 2003 Silverado LB7 diesel. It gets occasionally down to -25°c where I live.

I can't decide what to do. I have free access to 5w30 and 10w40 Motul Tekma+ oils. Using 5w30, cold start lubrication is not a problem, but the viscosity is thinner at operating temp.
Using 10w40, cold start lubrication could be a problem, but the viscosity is what the engine calls at operating temp.
It's a small sacrifice both ways.

Please help and point me in the right direction.

My answer: yes.

 

[Nesterenko]

Using 5w30, cold start lubrication is not a problem, but the viscosity is thinner at operating temp.

Not really, lots of 30 grade oils have HT/HS of 3.5, like some 40 grades.