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I've noticed that the recommended motor oil weights for cars in the last 5-10 years are often lower than earlier models. It seems like 10w-30 used to be almost ubiquitous in the 80s and early 90s, but now I'm seeing manufacturers recommend 5w-20 and 0w-10.

What does this change imply? Could it indicate improved engine design or manufacturing techniques? Tighter tolerances?

Or is it related to something else?

Matt
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3 Answers3

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Two words, fuel economy.

Using a thinner oil allows manufacturers to eek out a little more fuel economy. Thinner oil flows a little easier and has a little less resistance.

To use the thinner oil, as you suggested, the tolerances inside the engine have gotten tighter. The tighter tolerances require new manufacturing techniques.

vini_i
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Better engine manufacturing quality control permitted less bearing clearance. Lower viscosity oils are needed in the smaller bearing clearances to permit enough oil flow to keep bearings cool ( bushing type bronze primarily but also good for rolling element hard steel bearings). Secondary advantage; lower shear resistance in thin oils makes less resistance and higher fuel economy. Also less cranking resistance on a cold start. I remember long ago , trying to start a car in exceptionally cold Chicago weather , kept the battery warm in the apartment overnight. Next morning put it in the car ; the engine turned over about twice and stopped , after market oil pressure gauge said 30 psi oil ; 10 W30 oil.

blacksmith37
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about right but the main reason for thinner oils is that of making engines more efficient and better environment friendly. To make a 4 stroke engine "cleaner" requires the engine to run or turn over faster..to do that they have to have shorter strokes which leads to a small engine and thereby smaller oil galleries to transfer oil around the rotating parts (90% of wear is produced in the first few revolutions of the crank when starting before hydrodynamic lubrication is achieved...hence the use of low viscosity oils...the 10 in 10w/30 is the oils viscosity at 40 Deg C and the 30 is the oil viscosity at 100 Deg C....So having an oil Ow/30 means the oil will get to those rotating parts a bit faster at the lower temperature

pipes
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