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5W40 Versus 10W40

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I have been reading a bit about oil lately and am slightly confused about something.

If the "W" refers to the low temperature rating of the oil and the other number the high temp rating what reason would anybody choose 10W40 over 5W40 or even 0W40 oil?

5W40 is better for colder starting temps than 10W40 and the same as 10W40 at full operating temps... So, why doesn't the industry get rid of everything but 0W40?

Am I way off base?

Thoughts?

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I have been reading a bit about oil lately and am slightly confused about something.

If the "W" refers to the low temperature rating of the oil and the other number the high temp rating what reason would anybody choose 10W40 over 5W40 or even 0W40 oil?

5W40 is better for colder starting temps than 10W40 and the same as 10W40 at full operating temps... So, why doesn't the industry get rid of everything but 0W40?

Am I way off base?

Thoughts?

a lot of that info you are might be reading might also be 30yrs old.

today oil has come a very long way, with 20-50 being able to be used at temps of 50 deg to 120 deg. and 10-40 below freezing to 100+ temps,

here is what to look for as for.

API SL/CF, CI-4 Plus

API SJ, SH, SG...

MIL-PRF-2104G

JASO MA (Motorcycle)

here are some numbers of some more modern 10-40 oils

Kinematic Viscosity @ 100°C, cSt (ASTM D-445)

14.4

Kinematic Viscosity @ 40°C, cSt (ASTM D-445)

84.5

Viscosity Index (ASTM D-2270)

178

CCS Viscosity @ -25°C, cP (ASTM D-5293)

5429 (-25)

Pour Point °C (°F) (ASTM D-97)

-43 (-45)

Flash Point °C (°F) (ASTM D-92)

230 (446)

Fire Point °C (°F) (ASTM D-92)

250 (482)

High Temperature/High Shear @ 150°C and 1.0 X 106 s-1, cP (ASTM D 4683), cP

4.3

Four Ball Wear Test (ASTM D 4172 @ 40 kgf, 150°C, 1800 rpm, 1 hour, Scar in mm) 0.40

Noack Volatility, % weight loss (g/100g) (DIN 51581)

6.7

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But what does the 10W afford me that the 5W does not in the context of motorcycles?

Thanks!

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10W performs better above certain temps as it is a bit thicker than the 5W. If your in 80+ temps 10W is the better choice. Beyween 60 and 80 its about even and below 5W is better

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if i read the specs right the new modern 10-40 perfrom better then the standard 5w even below 60 deg.

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No, about the sameperformance from 60-80. The 10W performs better above 80 degrees. The 5W will do better below 60.

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But regardless if it's 60 or 80 ambient and your oil temps are 212*F the 5W and 10W are the same viscosity at at 212*F as per the 40 rating.... correct?

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Someone will correct me if I'm wrong but I believe the 10W has a heavier base oil than the 5 and viscosity improvers are used to get the 40 rating when hot. Thus for high temp performance and longevity of the oil it is better to use the 10W.

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But regardless if it's 60 or 80 ambient and your oil temps are 212*F the 5W and 10W are the same viscosity at at 212*F as per the 40 rating.... correct?

Not 100% correct, the engine has a harder time cooling in hotter temps which actually means it will be hotter temp wise. Also the starting temp has alot to do with it. The 5W wont protect as well on startups as the 10W will, because it will be spread much thinner because of the higher temps. The 10W though will be thicker than the 5W before start up so in cold temps it will be like kicking over sludge.

Someone will correct me if I'm wrong but I believe the 10W has a heavier base oil than the 5 and viscosity improvers are used to get the 40 rating when hot. Thus for high temp performance and longevity of the oil it is better to use the 10W.

Correct

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I'm starting to understand this a bit more at the technical level...

5w is a thinner base stock than the 10w,

At 212*F regardless of the W rating, the 40 means that it is no thinner than straight 40 weight oil the same temp...

A 5W oil (organic) requires 2X the number of Viscosity Index Improvers than 10W, so twice as much VII (which are not lubricants) are required in 5W 40 than 10W 40. It is the VII's that break down due to shearing forces like transmissions in a bike so it's not that the oil is less viscous at 212*F... the 5w high rating will break down twice as fast as the 10w... unless you go with synthetic which doesn't need near as much in the way of VII's. Without VII's to break down a 5W 40 synthetic should be much better than 10W 40 organic at 212*F.

Even though the oils are rated the same at the high temp... I suppose that doesn't mean they will behave the same at any other point of the scale either.

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I'm starting to understand this a bit more at the technical level...

5w is a thinner base stock than the 10w,

At 212*F regardless of the W rating, the 40 means that it is no thinner than straight 40 weight oil the same temp...

A 5W oil (organic) requires 2X the number of Viscosity Index Improvers than 10W, so twice as much VII (which are not lubricants) are required in 5W 40 than 10W 40. It is the VII's that break down due to shearing forces like transmissions in a bike so it's not that the oil is less viscous at 212*F... the 5w high rating will break down twice as fast as the 10w... unless you go with synthetic which doesn't need near as much in the way of VII's. Without VII's to break down a 5W 40 synthetic should be much better than 10W 40 organic at 212*F.

Even though the oils are rated the same at the high temp... I suppose that doesn't mean they will behave the same at any other point of the scale either.

Correct, though what Ive been telling you from the start will hold true in any Syn vs syn or org vs org comparison. I know honda has a scale as to which oil to use at what temp so figuring which one is best for you should be easy. Generally the hotter the temps the heavier oil you will use.

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Generally the hotter the temps the heavier oil you will use.

What I was trying to get at is that 5w 40 and 10w 40 are the same viscosity at 212*F. The only thing we know about 10w is that it's heavier oil at 32*F which means nothing at 212. We need to go to a 50 weight oil to be more viscous at 212*F than 40 weight.

I have that same scale in my Kawi manual, but I was hoping to understand why I should use 10W40 instead of 5W40 for my temperatures and it really comes down to not having to change the oil as often with the 10w.

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Yes and no in a synth versus synth comparo there are still more VII in it to get the 40 rating. the base weight helps somewhat in higher temps, its like a football player wearing what they call a skleton under his shoulder pads. Its a small layer of padding, its just exrtra protection. Kind of the 5W versus 10W, theres a bit thicker base helps resist the thinning out of higher temps better. Both say 40 in top but its really a 39 and a 41.

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Even better, run a deisel oil. It's 15W40.

Seems to me the less you have to rely on the VII's the better.

Went riding out in the Mojave on Wednesday. It was probably 90 before we even started the bikes. I would have preferred running straight 40 weight oil.

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