Oil weight question

[901Memphis]

Originally Posted By: Gene K
Originally Posted By: 901Memphis

The SAE 30 will be impossible to crank below 0F.


That's not 100% accurate. SAE 30 just means its VII free and says nothing about its cold performance.



Actually the sae grading tells you how it performs in the cold. A VII free 10w30 synthetic will crank much easier than a mineral sae 30, but like I said in the post you quoted I was just trying to help him understand a little about the differences.

 

[Merkava_4]

Originally Posted By: 901Memphis
I'm sure it makes sense in your head but to the rest of the world your stating that the 5w30 is thinner when cold than hot which isn't true.


Thinner when cold than hot? Where the heck did you get that idea?

Let me explain it this way:

5W-30 is the weight of a 5 weight oil at the surrounding ambient temperature before you turn the key. At full operating engine temperature, 5W-30 is the same thickness of a 30 weight oil when a 30 weight oil is hot. 5W-30 will be thinner than SAE 30 at any given ambient temperature before you turn the key. Is it thinner when it's hot than when it's cold? Absolutely. Is it thinner than SAE 30 when SAE 30 is cold? Absolutely. 5W-30 is basically two oils in one bottle.

 

[Shannow]

Gene is right, the VII free 10W30 IS an SAE30 oil...and will therefore have the same cold performance as a 10W...in an SAE30 should the maker choose to label it only as an SAE30.

 

[Garak]

Originally Posted By: Merkava_4
5W-30 is the weight of a 5 weight oil at the surrounding ambient temperature before you turn the key. At full operating engine temperature, 5W-30 is the same thickness of a 30 weight oil when a 30 weight oil is hot.

Your general idea of multigrades is correct, but your definition is off. Review SAE J300 charts. The number before the "w" is determined by cold cranking results at given temperatures. The number after the "w" is determined by kinematic viscosity.

Look at the definitions of a 20w-20. That is not a monograde and is decidedly not the same as an SAE 20.

 

[MKZman]

Originally Posted By: 901Memphis

The SAE 30 will be impossible to crank below 0F.
The 0w30 will crank down to probably -30F or so (Maybe colder!)
The 5w30 will crank down to probably -25F for a mineral oil
The 10w30 will crank down to probably 20F or so.


I am sure not what data this is based upon but 10W-30 cranks well below 20 F. Most application charts I have seen have 10w-30 usable down to -5 F or so. I see the battery is as much a variable at low temp starts as the oil.

 

[fdcg27]

Originally Posted By: MKZman
Originally Posted By: 901Memphis

The SAE 30 will be impossible to crank below 0F.
The 0w30 will crank down to probably -30F or so (Maybe colder!)
The 5w30 will crank down to probably -25F for a mineral oil
The 10w30 will crank down to probably 20F or so.


I am sure not what data this is based upon but 10W-30 cranks well below 20 F. Most application charts I have seen have 10w-30 usable down to -5 F or so. I see the battery is as much a variable at low temp starts as the oil.


Yeah, 10W-30 and 10W-40 are actually among the grades allowed for in the OM of our '09 Forester down to -4F.
I also used 10W-40 dino for years here and had many below zero starts with no drama.
OTOH, the '12 Accord doesn't crank with much authority on HGMO 0W-20 on a -10F morning, but that's a battery issue and has nothing to do with the oil, as you note in your post.

 

[440Magnum]

Originally Posted By: 901Memphis
Originally Posted By: Merkava_4
SAE 10 is a 10 weight all the time. 5W-30 is a cold 5 weight and a hot 30 weight. Plain and simple.


I'm sure it makes sense in your head but to the rest of the world your stating that the 5w30 is thinner when cold than hot which isn't true.

http://www.sae.org/news/releases/rightoil.htm


What he's trying to say us that a 5w30 at operating temp is the same thickness as a 30 weight at operating temp (true), and a 5w30 at room temp is the same thickness as a hypothetical SAE 5 at room temp (sorta the right idea, but not correct since the "5w" isn't measured by kinematic viscosity).

I used to think of it the same way before I realized how much better it is to think of the oil's "natural state" as being at a operating temperature and then the first number as a measure of how much it thickens as it cools.

 

[ElastoHydro]

To illustrate, I've done this experiment: Take a 5w-20, 0w-40, and 5w-30 down to about 0 degF, or whatever your freezer can do. Even though there is that "0w" in the 0w-40, thats the thickest one. (All synthetics here.)