Oil weights

[wn1998]

After searching the site and internet I have yet to find a chart expaining oil weights. I read people talking about 5W30,15w40 and ever 5w20 and don't really understand the different weights. I have heard people talk about some oil being "too thick" and robbing performance and some oils that are too thin. Could I get a quick expanation of 30wts vs. 40wts?

 

[sbc350gearhead]

http://www.bobistheoilguy.com/visc.html

 

[Ken2]

http://www.infineum.com/information/viscosity.html

The cold cranking viscosities are in a device that measure the resistance to turning a part in that cold oil. The hot viscosities are the time it takes the hot oil to flow through a certain orifice.

As you can see from the chart, so-called multigrade oils meet both a cold viscosity test and a hot viscosity test. "weight" is not a very descriptive term. Viscosity is described as the resistance to flow. Higher viscosity fluids, like cold pancake syrup, flow slowly. Lower viscosity fluids, like hot syrup, flow faster. Higher viscosity oil has higher film strength for more bearing protection, requires more power from the engine turning in this thick oil, and sometimes cannot flow properly into small oil passages. The engine designers determined which viscosity oil works best in their engine (we can debate the fine points, but this covers most of the basics).


Ken

 

[Al]

The thing to remember is that the first numbers 10W, 5W, etc. are a measure of how low a temperature the oil can pump at. 0W is lower than 5W, is lower than 10W.

The second number gives viscosity in Centestokes (cSt.) The higher the number the thicker. This is always measured at 100C or 210F. So that's essentially how "thick" the oil is when it is up to operating temperature.

Also bear in mind..no matter what the first number is ie. 5W-the oil will always get thicker as it cools down.

 

[Ugly3]

Here is a link that tells you more than you ever wanted to know.

API Data

 

[wn1998]

SO you should use a 5w oil if the temp drops below 0 degrees. What oil weight should you use if the summers are regularly in the upper 90's?

 

[Ugly3]

wn1998 - SO you should use a 5w oil if the temp drops below 0 degrees. What oil weight should you use if the summers are regularly in the upper 90's?

Well, that is easy. Whatever viscosity the manual indicates you should use. Generally 5w30 would do fine but some makers recommend differently.

 

[Al]

quote:

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Originally posted by wn1998:
SO you should use a 5w oil if the temp drops below 0 degrees. What oil weight should you use if the summers are regularly in the upper 90's?

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Yea-go by the manufactures recommendations. But remember oil is always thicker when it is cold. So in theory 0W, 5W, 10W, even 15W oil would be fine in hot weather. The advantade of 10w30 oil compared to 5w30 oil is that less viscosity improvers are used (in 10W) so in "theory" the 10W oil would hold its grade a bit better, possibly>