Hi all,

I am looking at a few different oils for my road car (Renault Clio Sport - which I don't believe are sold in the USA)

There are three oils that I am interested in

Elf 5w-40 Exillium
Redline 5w-40
Castrol 0w-40 The Edge

*Note : all of these many be marketed differently in various countries.

What I am trying to understand is that when I compare various technical datasheet values what am I looking for? higher / lower value? and how does the rating work - linear? or exponentially / or inverse exponentially.

Vis @ 100c cSt
Redline = 15.1
Castol = 13.5
Elf = 14.3

Is castrol's better then Redline? with the 1.6 point different, does that mean one is better then the other by 11%? or is the different not linear?

Viscosity Index
Redline = 170
Elf = 160
Castrol = N/a (no value given)

What does this mean? I know that Amsoil 5w.40 has a viscosity index of 182. is 22 points higher then Elf THAT much better?

High Temp High Shear Viscosity
Redline = 4.6
Castrol = 3.7
Elf = Not provided

To me, a 0.9 spread for such low values is alarming.. or is it a log curve?

Anything anyone can help me understand each value would be great!
Justin

quote:

Vis @ 100c cSt
Redline = 15.1
Castol = 13.5
Elf = 14.3

40 wt has a vis range and all above are in that range higher is thicker

Viscosity Index
Redline = 170
Elf = 160
Castrol = N/a (no value given)

Viscosity index is a mesurw of how much a oil thins as it gets hot normally higher is better meaning LESS thinning out when hot.

High Temp High Shear Viscosity
Redline = 4.6
Castrol = 3.7
Elf = Not provided

HTHS is a viscosoty mesurement at a high temp with a high shear higher is a thicker oil which will lead to better wear protection BUT also a thicker oil will slightly reduce gas mileage.

All are good oils best advice is change out routinely since ALL oils will start to get "dirty" and breakdown as soon as they are put in.
bruce
bruce

One thing I might add to Bruce's explenation is the simple definition I use to describe VI (Viscosity Index). VI is the oil's ability to stay within it's viscosity range. The higher the number the higher temp that it stay's in it's viscosity range. The lower the number the faster it falls out of it's viscosity range (thins out).

Understanding oil specifications.
This is a good question and the first place to start when looking for good oil.
Some oil makers do not publish or supply all the specs. These ones I am always leery of.
I look for the basic four.

Flashpoint: Often ignored. Flash is a good indication of good base oil stock. No modern day oil that I know of is under 400 F and this is a minimum number. The higher the flash the better. If an oil specs out at 400 F or slightly above, warning bells should sound. Good dino oils and synthetics are over 450 F. Synthetics often spec out over 500 F.

HTHS: Each viscosity range of oil has to meet a minimum hths requirement. 15/40 for instance would have to be 3.7 minimum. Look for oils with high hths. Over 4.0 is good depending on viscosity.

Viscosity Index: Higher the better. 140 should be considered minimum.

TBN: Higher the better. 10 or more is very good.

Better than flash point is NOACK volitility. Maxlife Synthetic 10w30 has a NOACK of 8.7, which is a pretty good number. Lower is better.

As for HTHS, I look at that as a good indication of how thick of a base oil you have, which would correlate with less viscosity index improver additive, in general.

Sporty car used for track days? If so the Redline esters and ZDDP moly may be worthwhile.