Lets have a mass debate on OIL

[volcano rs]

with a name like oilman who i'm i to argue with you when it comes to engine oils

[oilman]

The two important numbers in determining an oils performance and basestock quality are the HTHS and Noack Volatility %.

The HTHS number determines the oils resisitance to shearing and the higher the number the longer the oil will stay in grade. You can only compare oils of the same viscosity i.e. 5w-40 vs 5w-40 etc.
A typical 5w-40 should be no less than 2.9

The Noack volatility % is important because it indicates the oils quality. The lower the % that evaporated off at 250degC the better quality the basestock is, again the same viscosities should be compared. A typical 5w-40 should be no more than 13%

If you want some benchmark products quality-wise, these ones are hard to beat as they are proper synthetic pao/ester oils and not petroleum based or "hydrocracked" oils

Silkolene PRO S 5w-40
HTHS 4.07
Noack 6%

Motul 300V 5w-40
HTHS 4.51
Noack 7%

If you then compare the above to an off the shelf oil which is built to meet the minimum required specification this is what you will see.

Shell Helix Ultra 5w-40
HTHS 2.9
Noack 13%

When we talk about quality and stay in grade capability you need only to know what basestocks an oil contains to see whether an oil is indeed a true synthetic pao/ester or a highly refined petroluem oil.

If you compare Castrol RS 10w-60 and Silkolene PRO S 10w-50, you would expect to see the Castrol have the higher HTHS but this is not the case as the basestocks are not of the same quality as Silkolene, Motul or Mobil1

Silkolene PRO S 10w-50 - HTHS 5.11
Mobil1 15w-50 - HTHS 5.11
Motul 300V 15w-50 - HTHS 5.33

Castrol RS 10w-60 - HTHS 3.70

Unfortunately many oil companies do not quote these figures for obvious reasons.

Cheers
Simon

[oilman]

I mentioned "shearing" above also know as viscosity loss, this is an important factor when considering an oil and should be explained.

Why do oils lose viscosity with use?

Viscosity Index Improvers.

An oils viscosity will decrease as the engine temperature rises. Viscosity Index Improvers are added to reduce this thinning. They are a key addative in the production of multigrade oils.

VI Improvers are heat sensitive long chain, high molecular weight polymers that minimise the viscosity loss of the oil at high temperatures. They work like springs, coiled at low temperatures and uncoiling at high temperatures. This makes the molecules larger (at high temps) which increases internal resistance within the thinning oil. They in effect "fight back" against the viscosity loss in the oil.

"Shearing"

The long chain molecules in VI Improvers are prone to "shearing" with use which reduces their ability to prevent the oil from losing viscosity. This "shearing" occurs when shear stress ruptures the long chain molecules and converts them to shorter, lower weight molecules. The shorter, lower weight molecules offer less resistance to flow and their ability to maintain viscosity is reduced.

This shearing not only reduces the viscosity of the oil but can cause piston ring sticking (due to deposits), increased oil consumption and increased engine wear.

Like basestock quality, VI Improvers also vary in quality. As with many items the more you pay, the better the finished article and more expensive, usually synthetic oils are likely to incorporate better VI improvers. All other things being equal the less VI improver an oil contains, the better it will stay in grade by resisting viscosity loss.

Which oils require more VI Improvers?

There are two scenarios where large amounts of these polymers are required as a rule.

Firstly in "wide viscosity span" multigrades. By this I mean that the difference between the lower "W" number and the higher number is large for example 5w-50 (diff 45) and 10w-60 (diff 50) are what is termed as "wide viscosity span" oils.

Narrow viscosity oils like 0w-30 (diff 30) or 5w-40 (diff 35) require far less VI Improvers and therefore are less prone to "shearing".

Secondly, mineral and hydrocracked (petroleum synthetic oils) require more VI Improvers than proper PAO/Ester (Group IV or V) synthetic oils as they have a higher inherent VI to begin with, this is due to differences in the molecular structure of the synthetic base oils compared to mineral oils.

It is a fact that many synthetics require significantly less VI Improver to work as a multigrade and are therefore less prone to viscosty loss by shearing.

Cheers
Simon

[topsparky]

at least we've got that sorted then i'm going to bed

[MidnightBlueS2]

Now where did I archive those chemistry textbooks

Just kidding Oilman, your explanations are well appreciated I'm sure...

[Fat Audi 80]

Just ordered my First 10 Litres of Silkolene Pro S 10w50 from http://www.opieoils.co.uk which with the "healthy" S2Forum discount was good value!

Thanks to Simon "Oilman" for the advice and discount.

Cheers,

Steve

[Greg_S]

I will post some details about this properly on friday. Basically for the discount contact OPIEOILS and simon will provide you with a code to access the members area to get a discount on their products.

[dan_b]

@Simon - do you have any of the more technical details on the Millers racing oil than is available on their website that you use by way of comparason in your above posts? Its interesting and informative stuff.

[Fat Audi 80]

I will post some details about this properly on friday. Basically for the discount contact OPIEOILS and simon will provide you with a code to access the members area to get a discount on their products.

And thanks to Greg for setting it up!

Cheers,

Steve

[PeteRR]

Yeah, Cheers Greg!

[Jamo]

So are we saying 10W50 or 5W40 for homefried S2's?

I've let some other forums know about the site as well.

[Fat Audi 80]

I have gone for 10w50 with an AMD chip. I feel it is a good compromise between the "thick" 10w60 and "thin" 10w40

*waits for Oilman to come along with technical explanation*

Cheers,

Steve

[4WheelDrifter]

I would say 5W40 for you Jamo, 'cause you don't drive yours properly.
Can Oilman do 5 litres of Pro S for <£40? It's a shame you can buy it in 25 litre tubs.

[rotoryboy]

I would say 5W40 for you Jamo, 'cause you don't drive yours

That's cos he's getting old now

[Jamo]

That's cos he's getting old now

Bah!

And thanks 4wheeldrifter your soooo kind