10w30 vs. 15w40: Is there a difference?

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I see many folks here run them interchangeably. That said, is there that much of a difference between the two?
 
Originally Posted by Rand
A broad question deserves a broad answer.


so,

"Yes"



So it's more than say Castrol 0w30 and Castrol 0w40?
 
Originally Posted by kschachn
If there wasn't a difference then they would be labeled the same, right?


Just as I mentioned in my above post, right?
 
There are plenty of oil mixers in here and they blend all kinds of stuff....I have not heard of anyone blowing an engine yet doing this, but then again,,,no one would ever tell it.All those oil electrons mix pretty well, just saying...
 
Originally Posted by dlundblad
I see many folks here run them interchangeably. That said, is there that much of a difference between the two?


On paper, and per technical analysis?: Big difference

In real life, real world circumstances?: usually not, for most people

.

Engines that push oil very hard, right to the limits of failure will find the differences very quickly,
compared to say a 4.6 liter Ford which will run happily forever on whatever oil you put in it......
 
"Engines that push oil very hard, right to the limits of failure will find the differences very quickly,
compared to say a 4.6 liter Ford which will run happily forever on whatever oil you put in it....." Which is why thin oil is OK even if it scares me
grin2.gif
 
My Jeep spec'd 10w30 and would run well on it, from the thinner mainstream stuff to Rotella. Jump to a 10w40 and I would have engine knock at start up unless swapped in 1 quart of 5w20 (out of the 6). I tried to run straight 15w40 once and it knocked no matter what, I had to drain it. Yes there is a difference.
 
Same oil: 10W-30 is US measures while 15W-40 is Metric

That is why an American Honda manual can call for 5W-20 while the Russian manual lists 5W-40.

...
 
Originally Posted by ammolab
Same oil: 10W-30 is US measures while 15W-40 is Metric

That is why an American Honda manual can call for 5W-20 while the Russian manual lists 5W-40.

...


This is pretty spot on.
 
Yes.
A lot of engines would be happy on either one, but there are some cases where one or the other really does better.
6.0 Powerstroke does very well on a 30 weight, the 6.7 probably should run a 40 because the oil gets some fuel dilution.

Lets put it in terms we can all understand.
15w40 and 10w30

darklightbeer.jpg
 
Originally Posted by ammolab
Same oil: 10W-30 is US measures while 15W-40 is Metric

That is why an American Honda manual can call for 5W-20 while the Russian manual lists 5W-40.

...

Wait, what?
 
OP -

I will say this ... in terms of what's in the bottle, certainly there is a difference, as you inquire.
But as for results, there's rarely any distinction between the two. Wear data will not show any significant difference in just about any application.
 
My engine is a 4JJ1, in an Isuzu D-Max 4wd.

Factory oil is Besco Duramax 10w-30.

Other recommendations in the handbook are all 15w-40: Shell Rimula R3X, or R2 Extra or R2; Exxon Delvac MX; Caltex Delo 400 or Gold. And a few others listed.

I ran the factory 10w-30 oil for for about the first 2 years of ownership, and a DIY change of the oil every 10,000km.

Have had a Provent oil catch can fitted since day one, and would regularly drain approx 90mm of oil each change.

My local dealer stopped being an Isuzu franchise, and thus I lost access to the Besco oil.

So I changed to Delo 400, and have been using that since, so that's about another 2 years using Delo 400.

The Provent now captures approx 75mm of oil each time.

That's the only noticeable difference I have between using 10w-30 and 15w-40. The D-Max otherwise drives the same, the engine sounds the same and fuel usage is the same between the grades.

[Linked Image]
 
Originally Posted by KCJeep
My Jeep spec'd 10w30 and would run well on it, from the thinner mainstream stuff to Rotella. Jump to a 10w40 and I would have engine knock at start up unless swapped in 1 quart of 5w20 (out of the 6). I tried to run straight 15w40 once and it knocked no matter what, I had to drain it. Yes there is a difference.


Same for my son's 1999 Cherokee XJ with the I6; it specs 10w30. It gets 5w30.
 
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