If 10W40 is bad what about 20W50?
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Postmaster
Joined: Feb 2003
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If 10W40 is bad what about 20W50?
I've read that 10W40 has fallen out of favor because of the spread between cold and hot viscosities. If that's true then what about 20W50? It has the same spread. Wouldn't it have the same problem?
Post Fiend
Joined: Jun 2001
Posts: 5,228
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From: Running Springs CA
It is not the same thing because the relationships are not linear. Actually 5W-30 is nearly as bad as 10W-40. Im not talking about synthetics or blends here. The xW number is based on a Cold Cranking Simulator maximum viscosity at various temperatures, while the -xx number is based on the viscosity at a fixed temperature for all, the boiling point of water, 100C. SAE 20 is a completely different test from 20W, which is confusing.
Jim
Jim
Post Fiend
Joined: Jan 2000
Posts: 5,860
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From: Metro Detroit (Redford)
(All the following pertains to dino oil) Todays viscosity index improvers must be a lot better than the olden days. The Maxlife 10w40 I ran in my F150 held up very well and did not lose viscosity in 3000 miles. I think a 5w30 may be worse than a 10w40 because the base oil is much thinner. Likewise a 20w50 has a pretty thick base oil. The European Redline site has some info discussing that straight 30 weight actually can pass the test for 20w (and so would be a 20w30) and so with the addition of some viscosity index improvers it became 20w50. If so, then the base oil in 20w50 is quite thick. And I always thought the "w" number was a good proxy for the base oil--apparently not (so I wonder what they really are). Also I believe 10w40 has a thicker base oil than 10w30, just to help minimize the extra spread. I suspect 20w50, 15w40, and 10w30 are the tightest spreads. 5w20 probably also is pretty tight.
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