2025 3500 RAM 6.7 Cummins; 10w30 vs 5w40

[Fishstyx]

Hate to open this can of worms ...
Like the title says. Watching YouTube and a guy driving his 2025 3500 RAM Laramie with the 6.7 Cummins was giving his take on using 5W40 and 10W30. He stated that his engine ran better with 10W30 over the 5W40. Better engine response. I know where he’s driving at it’s close to my home so I am very familiar with the climate and geography of the area with the mountains and high plains desert. I prefer to run 5W40 viscosity year round but if the engine runs better on 10W30 then I will definitely run that. Let’s open this can of worms and see what everyone else has experienced.

 

[kschachn]

“Hate to open this can of worms”.

And yet, here we are.

 

[SC Maintenance]

So another seat of pants dyno meets placebo affect YouTube video you say?

 

[wwillson]

He stated that his engine ran better with 10W30 over the 5W40. Better engine response.

Pure hogwash, nothing but butt dyno confirmation bias.

 

[kschachn]

Pure hogwash, nothing but butt dyno confirmation bias.

But when that’s all you got, that’s all you got.

 

[6.7 CTD]

5w40 year round

 

[#18FAN]

We could be talking about a 15w40 in it.

 

[NiwradND]

“Hate to open this can of worms”.

And yet, here we are.

5w40 year around in my 2021, but I often wondered if 5w40 and 15w40 was the same thickness when at operating temperatures why 15w40 doesn't work in very warm climates. I think 10w30 would work fine in warm winter and cool summer climates, but i like the extra protection of 40 weight oil.

 

[daniel327]

It would run even better if he used Valvoline oil.

 

[Pablo]

0W-40

 

[JohnnyG]

It would run even better if he used Valvoline oil.

Good old S3 Valvoline, straight SAE 30. Saw many a Mack truck with 1,000,000 miles or more on the clock using that !

 

[GMBoy]

No 10w30 is going in any Diesel I own. What's next? Somebody is going to run 0w20 in their Diesel?

 

[Pablo]

No 10w30 is going in any Diesel I own. What's next? Somebody is going to run 0w20 in their Diesel?

GM

 

[GMBoy]

GM

What does that mean?

 

[Pablo]

What does that mean?

GM dexosD 0W-20

 

[Fishstyx]

So another seat of pants dyno meets placebo affect YouTube video you say?

Pretty much

 

[Fishstyx]

We could be talking about a 15w40 in it.

No he was saying 5W40

 

[fantastic]

"Engine runs better" can mean so many things. Only 40 grade oil in my Power Stroke. Does this YTer live in Alaska? I could see that making a difference in starting etc.

 

[kschachn]

Pretty much

So this is what you thought before you created the thread?

 

[RBT]

So this is what you thought before you created the thread?

That might be giving too much credit.