In current name brand oils is there any reason not to always use 5 W30 instead of 10 W30?

Joined
Jan 25, 2003
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Decatur AL USA
My flawed system.

5W-30 if it has an equal or greater flashpoint. To me that's an indication of superior base.

10W-30 if it has the higher falshpoint.

I default to 10W-30 when flashpoint is unkown.
 
Joined
Oct 22, 2009
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Wet side WA
With modern oils is there any reason not to always use the lowest cold rating with the same operating temperature rating oil? I have read that in the past 5 W30 oil had more additive and was less shear stable than 10 W30 but does that still apply today? Also even if my manual doesn't mention it, because it wasn't invented in 1992, is they any reason not to use 0 w30 oil in a car that calls for 5 or 10 W30 oil. It is my understanding that the first number is the viscosity when cold. Why not use the lowest cold rating while keeping the "hot" rating?
Well where you live there may be some benefit but me I live out here on the Coast I don't need 0W oil and many times I find 10W oil on sale not so much with 0W oils.
 
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May 17, 2021
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open range
.
Thanks to OilUzer and Overkill in particular for their excellent contributions.
I feel sobered up so many poster seem to have issues realizing that 'all things
being equal' is quite far from being realistic. Things aren't equal and there's
a good reason why 5W-30 dominates the VW 504 00, MB 229.5/51 and LL-04
offerings. Anyway, the die-hards will keep on using commonly mediocre base
oil 10W-30 and still feel good with it.
.
 
Joined
Jan 25, 2003
Messages
5,346
Location
Decatur AL USA
.
Thanks to OilUzer and Overkill in particular for their excellent contributions.
I feel sobered up so many poster seem to have issues realizing that 'all things
being equal' is quite far from being realistic. Things aren't equal and there's
a good reason why 5W-30 dominates the VW 504 00, MB 229.5/51 and LL-04
offerings. Anyway, the die-hards will keep on using commonly mediocre base
oil 10W-30 and still feel good with it.
.

Is a 10W winter rating allowed for those specs currently? If so, which ones?
 

OVERKILL

$100 Site Donor 2021
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Ontario, Canada
Is a 10W winter rating allowed for those specs currently? If so, which ones?
Mercedes allows a 10W-xx:
Screen Shot 2022-03-12 at 5.36.46 PM.jpg
 
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