Engine Oil Explained…a bit (aka Part 1)

This is a post I penned in 2010...but it's still relevant and interesting...I think... :-)

5W30? 10W40?  Ever wondered what it meant?  Even if you do know what it means… a few interesting facts may follow.

 The 5W30 is a designation of the engine oil weight.  To break down the information lets create a “formula”:  “1st Number” “1st Letter” – “2nd Number”.  The 1st Number and  1st Letter actually go together – the letter:  W in our case indicates the temperature and the 1stNumber indicates the viscosity measured in centistokes (cSt).  W means winter and would indicate that the temperature of the testing was 0 degrees C (32 degrees Farenheit).  If there was no letter it would indicate that the temperature was 100 degrees C.  Which is why the 2nd Number has no letter following it; It is the viscosity of the oil at 100 degrees C.
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    ⁃    What exactly is viscosity?  It’s basically how thick a fluid is.  For example, compare water and molasses (at room temperature).  Water is less viscous than molasses.  Comparing these two fluids is a good example to compare the engine oil at two temperatures.  Think of oil at 0 degrees C as molasses and oil at 100 degrees C as water;  water would flow through the engine easier.

I’ve always taken for granted that there were 2 numbers and a letter for oils, but after doing a bit of research, I found that the 2 numbers actually means it’s a multi-weight oil that has had polymers added to it.

Engine Oil Numbers