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the high temperature designation - right? So then why does our manual (& Castrol website) show that 5w30 has a high temp. of 95*F yet the 10w30 is above that. Shouldn't the "30" in both grades reflect the same high temperature, whereas the 5w or 10w indicates the different low temperatures?


Thanks for your help..
(I did try "search" and "faqs" but came up empty
)
 

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Isn't it the consistency of the oil at a certain temperature?
i.e. a 30 is thinner than a 40?

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the w means winter weight so, i believe the 10 is normal viscosity and the 30 is cold viscosity... pretty sure about that.
 

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i.e. if it's 5w30... the 5 viscosity is when you start the car.. and the 30 viscosity is after you warm up your car..

the higher the number, the ticker the viscosity which protects your engine. that's why in cold weathers it's recommended you use 5w30 oil, so when you start your car, the oil car get into engine parts quicker.

i may be totally wrong on this.. hehehe
 

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Multi-viscosity oils include polymers to allow the oil to to behave like an oil of lower viscosity at a lower temperature. The "W" designation means suitable for winter use. 5, 10, 15, and 20 are all eligible for "W" designation. So technically, a straight 20 could be considered W20.
The polymers can shear off the of oil molecules, and the wider the range of the oil, the more difficult to prevent the shearing.
What you want to do is use oil with the smallest viscosity range for the temperatures that you expect to encounter. Since oil is changed 2+ times a year, a 5W30 might be suitable for the winter, but a 10W30 would be better for the summer.
A 20W50 would be better yet for summer use. Even though the 30 spread is high, the heavier weight oil to begin with doesn't require the same polymers that a 10W40 would.
so to answear why Honda shows 5W30 to 95F, and 10W30 higher, they both should have the same SAE30 viscosity characteristics above 95F, but you're going to be more likely to effect the polymers at those temperatures with the 5W30 than the 10W30.


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Yeah, you're right. The first number, with W after it, is the low temperature viscosity rating, and the second number is the high temperature viscosity rating.

As for why two oils with the same high temp rating have different specs from the manufacturer, it most likely has to do with two different rating systems. The 5W-30 10W-30 etc ratings are prescribed by SAE, while the temp ratings you saw are probably based on some internal standard that only that oil company uses. In other words, that oil company is making more of a distinction than the SAE standards do.

At least that's what makes sense to me.
 

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Discussion Starter #7
<font face="Verdana, Arial" size="2">Originally posted by ed'98:
so to answear why Honda shows 5W30 to 95F, and 10W30 higher, they both should have the same SAE30 viscosity characteristics above 95F, but you're going to be more likely to effect the polymers at those temperatures with the 5W30 than the 10W30.
</font>
Thanks everyone.. appreciate the help.

ed'98: Thanks man...i agree, just wasn't sure. Anyway, i put in 5w30 yesterday.. i'll go back to 10w30 in July. Just wanted to make sure i'll be ok if temps go above 100F before then(and sometimes they do in CA).
 
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