Viscosity test 1 Liter (1.06 quart) motor oil 5w-40 tested at +1 C and +80 C Oil tested: Statoil Lazerway Euro 4 edition friction fighter C 5w-40 with approvals by VW 505.00/505.01/502.00 MB 229.31, BMW LL-04 and ACEA C3/A3/B3/B4, API SL/CF I have heard professionals explain the SAE oil viscosity scales in several different ways; mostly wrong in just about every aspect. Here's a favorite. The expert compares the two grade ratings on; say a 10-30 multi-grade oil and states that the 10 is thinner than the 30. That is incorrect. Multi-grade oil is measured differently on the first index versus the second. The first is measured on a.o. "pumpability" at subzero temperatures; specifically a 10W is measured at -25 degrees Celsius and subsequently assigned its index number. The second rating is measured at 100 degrees C and is an expression of how thick the oil remains at that higher engine operating temperature. The 10 is therefore not thinner than the 30 but rather a guarantee that the oil is sufficiently free flowing at -25 degrees Celsius, so at to provide ample lubrication of the engine. The 30 is an orange and the 10 is an apple... I've also heard "experts" state that modern multi-grade oils "gets thicker with the rising heat" and hence, the oil gets to be 30 in viscosity when it hits the operating temperature. Now we have total confusion. Due to thermal viscosity breakdown, any oil will be thinner at 100 degrees Celsius than at -25 degrees Celsius. It is correct that there are additives added to mineral oils to prevent the paraffin from solidifying at lower temperatures and furthermore, there are polymers added that thicken as the temperature rises. However, the oil is nevertheless thicker at cold temperatures than it is at high temperatures. The 30 index just indicates that it remains sufficiently thick for most normal passenger car engine applications while running within normal operating temperature ranges. To clear this up, I made the little video with a high grade modern motor oil which shows conclusively that a 5w-40 isn't "5" when it's cold and then "40", or thicker when it's hot. Test setup: Poured through 14 cm long funnel with opening diameter of 6 cm and end tube diameter of 8 mm. Ambient temperature +1 C (+34 F); oil approx. the same at initial test Tested cold 5 times. It took from 1 min 38 secs to 1 min 49 secs. Variation stemmed from pouring down the sides and letting it almost drain before refilling; which was slow, to pouring constantly and aiming for the small hole in the funnel which caused the funnel to empty much faster. Oil subsequently heated to a temperature of +80 C (+176 F) resembling engine operation temperatures. Tested hot just 2 times as it was immediately evident the oil was much thinner. Regardless of pouring method, the funnel drained in just 19 to 21 secs. Conclusion. Oil does not get thicker when it gets hot (but you already knew that). The polymers that expand with heat does make the oil thicker than it would otherwise be but it is still a lot thinner than when cold.

• published: 22 Jan 2012
• views: 4523