Curious what the oil viscosity index means.

I noticed the following differences (all 20W-50):

Mobil 1 Index is 142
Amsoil Index is 155
Redline Index is 165

Why the difference between them?

 

Has to do with how much they stray from their viscosity ratings at a given temperature range. The higher the index number, the more the oil stays true to its viscosity. These are all pretty close, but in your example the Redline holds its viscosity more than the Amsoil, which holds its viscosity more than the Mobile 1. I don't think these differences here are very significant

 

Thanks.

That's kind of what I was thinking. You think there is any difference in the base stocks between them (Group 3 versus Group 4)? I know allot of folks tout the M1. Just wondering why the M1 viscosity index is lower than the others. I couldn't find anything online saying what base stock M1 uses. I saw that RL said it is a PAO (4) and I'm assuming Amsoil is as well based on the high VI. Kind of wanted to stay away from the viscosity additives if I can. Any thoughts?

 

Just go and get some Shell Rotella and be done with it. Put the saved cash in your fuel tank.

 

I believe that Amsoil is group 4, Red Line is group 5 and I'm not sure what group M1 is in, I'd guess possibly 4. Group 3 syn oils are made from crude oil base stock, and I don't believe M1 is made that way. I don't think the differences in the index numbers mean too much here- to me they are just minor testing differences, in the real world I suspect there isn't too much variance to matter. These numbers are all very close to each other. I'd not hesitate to use any of these.

 

How many miles have you been running 15W-40?

 

I've been running it for 30,000. I have almost 70,000 on this engine.

 

Does it handle the heat well? How do the lifters and rockers sound compared to 20W-50?

 

Handles the heat well? I live in Florida, it's hot here, so, I guess it does.
Engine doesn't sound any different than running 20W-50. Pretty quiet as far as I can tell, no baffles will quiet anything else I guess.

 

Mobil Syn, is a #3 Basestock, Google Mobil vs Castrol, lawsuit! AMSOIL & Redline use both basestocks #4 & #5, depending on application?

I wouldn't use Rotella Diesel, it doesn't Test very well, in trucks & it won't pass H-D's warranty ?