Engine Oil Grades - what does it mean?

[sleepsus]

For those who wanted to know what those numbers on the engine oil bottles mean and how it relates to your car's engine, here is a good read :

HowStuffWorks "Choosing the Right Type of Motor Oil"

Viscosity, at its most basic, is a fluid's resistance to flow. Within the engine oil world, viscosity is notated with the common "XW-XX." The number preceding the "W" rates the oil's flow at 0 degrees Fahrenheit (-17.8 degrees Celsius). The "W" stands for winter, not weight as many people think. The lower the number here, the less it thickens in the cold. So 5W-30 viscosity engine oil thickens less in the cold than a 10W-30, but more than a 0W-30. An engine in a colder climate, where motor oil tends to thicken because of lower temperatures, would benefit from 0W or 5W viscosity. A car in Death Valley would need a higher number to keep the oil from thinning out too much.
The second number after the "W" indicates the oil's viscosity measured at 212 degrees Fahrenheit (100 degrees Celsius). This number represents the oil's resistance to thinning at high temperatures. For example, 10W-30 oil will thin out at higher temperatures faster than 10W-40 will.

[Bitulo]

In choosing which oil to use, there are two basic information that one should know: the viscosity grade which is indicated by the SAE number and the API grade. The SAE grade (Society of Automotive Engineers) shows how thick is the oil at operating temperature, i.e., 210 degrees F. The SAE 50 is thicker than SAE 40 and SAE 40 is thicker than SAE 30. In the Philippines where the temperature is relatively hot, recommended oil is SAE 40 and SAE 50. The right thickness is indicated in your car owner's manual. The SAE 50, SAE 40, SAE 30 are so-called single grade or monograde oils and SAE 10W-40, SAE 20W-50 are called multigrade oils. Under normal conditions, the multigrade oils are more expensive, but they provide better protection for your engine especially if you go to colder areas like Baguio once in a while. The rule of thumb is use whatever is the SAE grade in your car manual. Using thicker than recommended will unnecessarily burden your engine, but using lighter oil on the other hand may shorten your engine life.

The API grade indicates the quality level of the oil. Latest model cars are recommended to use API SM grade which is the highest level at this time. Older cars usually are recommended to use lower API grades like API SL, SF, SG, SE, SC (the lower the alphabetical designation the lower the quality level). Whatever model the car is, it can benefit by using the highest API grade available in the market. However, for those who want good protection for the engine at reasonable cost, the best bet is to stick to the recommendation of the vehicle manual. However, exceeding the API recommendation is a good practice for better engine protection but more costly.

[dvldoc]

If you every mix grades you might find this very handy.

Mixing viscosities

[hinDMaxsiado]

The TRUE viscosity of oil is NOT in the label of the package.... Those written in the label are just "indicative", not exactly the true oil weights nor viscosity.

True viscosity is measured kinematically and is given in centiStokes.... There are oil that are written as lightweight oils but are in fact a bit heavier when measured in their true dynamic viscosities at diferrent temperature levels.... There are even those that are written a bit heavier but are in fact not that heavy when you see their kinematic viscosities....

i purchase my oil based on its kinematic viscosities at different temperatures, amongst many other factors.

[locoroco777]

how will the common people know if whats the kinematic viscosity of the oil their buying? because last time I checked, none is written on the label, whats there is only the API rating, and winter temp and viscosity rate...

[indiej]

two 5w30 oils: one is 70 cSt at 40 deg C, the other 50 cSt same temp.

Is that at all significant especially at startup, when engine wear usually happens?
we have 30-35 deg C on good days, 22-28 deg C yuletide season. at lower temps both oils will have higher kinematic viscosity values.

[indiej]

how will the common people know if whats the kinematic viscosity of the oil their buying? because last time I checked, none is written on the label, whats there is only the API rating, and winter temp and viscosity rate...

you could search it in the net. e.g. below, i just googled that this minute


Castrol GTX
Method 5W-20 5W-30 10W-30 10W-40 20W-50
Viscosity * 100C, cSt ASTM D445 9.1 10.7 11.31 14.3 18.09
Viscosity * 210F, SUS ASTM D2161 56.1 61.7 63.9 75.2 90.4
Viscosity * 40C, cSt ASTM D445 51.77 64.31 75.1 108.3 159.1
Viscosity Index ASTM D2270 158 157 142 133 126
Low Temperature (C) Cranking
Viscosity, cP max. ASTM D5293 6,600 * -30 6,600 * -30 7,000 * -25 7,000 * -25 9,500 * -15
Low Temperature (C) Pumping
Viscosity, cP max. ASTM D4684 40,000 * -35 40,000 * -35 50,000 * -30 60,000 * -30 60,000 * -20
HT /HS Viscosity, cP min ASTM D4683 2.6 2.9 2.9 2.9 3.7
Pour Point, F (C) max ASTM D97 -44 (-42) -38 (-39) -22 (-30) -27 (-33) -27 (-33)
Flash Point, PMCC, C min ASTM D93 >200 >200 >200 >200 >200
Density * 15C, Relative ASTM D4052 0.862 0.862 0.878 0.887 0.884
Pounds per Gallon 7.18 7.180 7.314 7.387 7.364

* Due to continual product research and development, the information contained herein is based on products purchased in the U.S. subject to change without notification. Typical
properties may vary slightly.