Question on oil weight spread

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Jun 27, 2007
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In the '80s GM, IIRC, said quit using a 30 weight spread and go to a lower number. I changed from 10W-40 to 10W-30 in my Chevy and my oil consumption dropped to near zero. Now days there is more than a 30 point spread in many oils. Using a modern synthetic oil does the 30 or more spread make any difference? I'm talking about 0W-40 and 15W-50 oils foe example. TIA
 
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Oct 20, 2005
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Yes, it does make a difference, although not as much as with dino oils. As far as I know, dinos usually start to require viscosity index improvers (VIIs) for a spread of 25 or more, whereas synthetics can go as big as 30 without needing VIIs at all.
 
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Both dino and synthetic oils are better than in the 80s, and are still improving. It was very good advice then, and only a possible caution now.
 
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 Originally Posted By: Audi Junkie
No. "Spread"? Come on, this is an expert site.
It's a rule of thumb, expressed in simple language. Am I wrong? Educate me, expert.
 
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