Question on oil weight spread

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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
 
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.
 
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.
 
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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