Viscosity Index and JASO 1A for Z1 alternative

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So I was looking at all synthetic ATFs that officially claim they can be used in place of Honda ATF Z1. While comparing them I came across two ATFs that have distinctly lower VI than all others, yet their other specs are similar. Amsoil and M1 were the only ATFs that have a VI of ~170. All others (RP, RL, Castrol IMV, Pennzoil) have a VI ~200. Now M1 and Castrol IMV are the only ones that claim "exceeds JASO 1A requirements". and Amsoil and RP have the highest flashpoint, and RP also has the highest VI, but none of them officially claim "JASO 1A". So are VI and the JASO requirements both equally important for selecting an ATF as a replacement for Z1 ? Or does one outweigh the other ? It seems like Castrol IMV is the only choice if you want to consider both a higher VI and the Jaso requirement. Thoughts anyone ?
 
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I know nothing of JASO 1A, so I'm curious myself. I can tell you this: Amsoil ATF uses no VII's, so that explains why the lower VI vs. some ATF's which typically contain VII's.
 

MolaKule

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The actual standard is called, "JASO M315-2003 1A," for Japanese automatic transmission with slip lockup clutch or slip-controlled-lock-up torque converter systems and of course has good anti-shudder performance. The VI has little to do with meeting this performance standard.
 

youdontwannaknow

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so would it be correct to say that the JASO spec should take precedence over anything else in determining the suitability of the fluid for this purpose(honda atf subtitute) ?
 
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youdontwannaknow

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but when comparing all fluids that claim to "meet" Z1 requirements (I suppose thats what they mean when they say their fluid is "also recomended for the following applications"), then does the difference in VI and the exceeding of JASO requirement, or the lack thereof, bear any importance when deciding for or against that fluid ? or are those difference insignificant ?
 
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 Originally Posted By: Pablo
I know nothing of JASO 1A, so I'm curious myself. I can tell you this: Amsoil ATF uses no VII's, so that explains why the lower VI vs. some ATF's which typically contain VII's.
I agree with you on that. VI is fairly meaningless for a formulation unless you know how it has been achieved.
 
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