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?

  • @barbecue - that's actually correct, at least indirectly -- the lighter oil weights are used to improve fuel economy and fuel economy ratings are driven (at least in part) due to the desire to reduce greenhouse gases that contribute to global warming. – Johnny Oct 21 '16 at 18:44
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    Yeah, I was more thinking along the lines of warmer winters allowing lower viscosities. – barbecue Oct 21 '16 at 18:54
  • "10w-30 used to be almost ubiquitous in the 80s" - and in the UK, 20W-50 was the standard for a long time before that. I've still got an unopened can of 20W-50 Castrol GT-X somewhere.... – alephzero Oct 21 '16 at 19:50
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    @Johnny Doh, I'm an idiot, of course you're right. – barbecue Oct 21 '16 at 22:11
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    @barbecue - don't you hate it when you make a joke and some jerk comes in and explains why your joke is not technically correct? :) – Johnny Oct 21 '16 at 22:27

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.

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