11 replies to this topic

[oilman]

I said I would post this up a while ago but forgot, sorry! Here is an explanation of what it all means and some comparisons of some oils I have the data on. How to make a complicated subject uncomplicated is not easy so I'll try to explain in the best way I can why oils degrade (shear) with use and the easiest way to identify an oil that will "stay in grade" for longer. 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 increase the relative viscosity 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. The best quality ones are normally found in synthetic oils (Group IV - PAO / Group V - Esters) and it is important to understand that the less of these in the oil the better the oil will stay in grade. 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" 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" 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 are less thermally stable to begin with and this is due to the non-uniform molecules in petroleum oils as opposed to the uniformity of synthetics built in laboratories by chemists. It is a fact that some synthetics require little or no VI Improvers to work as a multigrade due to their superior thermal stability. How to identify a good "shear stable" oil. API and ACEA both conduct tests called HTHS (High Temperature/ High Shear) and all oils carrying these specifications are tested and scored. For all oils, these test results are available however, they are often ommitted from the oils technical data sheet! Oil Companies have a tendency to publish the figures that they want you to see and therefore you often need to dig further or ask for certain information when comparing the performance of various oils. High-Temperature/High-Shear This test is a simulation of the shearing effects that would occur within an engine. In fact, it's actually designed to simulate motor oil viscosity in operating crankshaft bearings. Under high stress conditions where shearing can occur, the VI Improvers (polymers) break down. As they do, the viscosity of the oil decreases. This is what the High Temperature/High Shear test checks for. The HT/HS test is measured in Centipoise (cP) as the Cold Crank Simulator test is. However, in this case, because you're hoping for the least loss of viscosity with an increase in heat and stress, you want the cP value to remain high. Each SAE multi-viscosity grade has a specific lower limit for the HT/HS cP value. If a multi-viscosity oil cannot achieve a cP value above that limit, it cannot be classified under that viscosity grade. For instance, according to the SAE specifications, an oil must achieve an HT/HS cP value of 3.7 or higher in order to be classified at the 15w40 viscosity grade. The thinner the oil the lower the number. Comparisons of HTHS numbers. Here for comparison sake are a few numbers that we have compiled from data sheets and requests to the oil companies concerned. These are well known oils and considered to be "quality" synthetics so these comparisons are relevant. Silkolene PRO S 5w-40 HTHS 4.07 Motul 300V 5w-40 HTHS 4.51 Silkolene PRO S 10w-50 HTHS 5.11 Motul 300V 10w-40 HTHS 4.19 Silkolene PRO R 15w-50 HTHS 5.23 Motul 300V 15w-50 HTHS 5.33 Mobil 1 Motorsport 15w-50 HTHS 5.11 Castrol RS 10w-60 HTHS 3.70 I'm sorry if this is too complicated but making a complicated subject simple is not easy however if I've lost anyone, please feel free to ask questions. Cheers, Simon

[jam]

I was just about to ask about that as well, thanks! So in summary, Pure virgin olive oil is better that sunflower.

[CupidKnewRap]

Learn somthing everyday Write an 'oil for dummies' book I think a compilation of your vx220.org posts would cover it .

[oilman]

Just one problem! You're not dummies, you know more about oil now. All you need to do is apply your new found knowledge. Cheers Simon

[engdan]

Very interesting post, however have I understood correctly ? Motul 300V 15w-50 with a HTHS = 5.33 has the "best" score from the oils listed and Castrol RS 10w-60 with a HTHS = 3.70 is the "worst" oil ? Or is it the other way round ?? Im not sure if a high or low HTHS number is desired ? How does std Mobil 1 0w40 compare ?? I have always used this in all my cars and if/when I get a VXT I would like to continue using it as Im led to believe its the best oil on the market ( based on engine tests I ran on the 2.2L L850 engine when I worked at Lotus) , however I would very much value an experts opinion on it.

[oilman]

Thicker oils will always have higher numbers (high is good but only compared against the same viscosity oil) however the most stark comparison is RS 10w-60 which should be highest against the 5w-40's of both Silkolene and Motul. This is down to basestocks, the Silkolene and Motul are true synthetics, RS 10w-60 is a hydrocracked petroleum oil and therefore as I've said before, not as shear stable. However you should really only compare viscosity with viscosity as it's not a fair comparison otherwise, i.e. a 15w-50 should always be higher than a 0w-40 but this is the tell tale sign to quality. The minimum for a 5w-40 to pass API and ACEA tests is 2.9 so with many oil manufacturers it's all they need to do, pass. Others build oils that exceed due to application, race and competition etc. Here are some 5w-40's but some of the data may be out of date. Name............................................................HTHS............ .....Noack Silkolene PRO S.............................................4.07....................6 Motul 300V....................................................4.51.................... 7 Motul 8100....................................................3.92.................... 10 Fuchs Titan Supersyn SL...............................3.90....................10 76 Lubricants................................................3.80.................. ..13 Shell Helix Ultra.............................................2.90....................13 Valvoline Syn Power ......................................2.90....................13 Chevron Supreme..........................................2.90....................13 Esso Ultron....................................................3.60.................. ..12 Mobil Synt S...................................................3.60....................12 API/ACEA minumum pass is HTHS 2.90 and NOACK 13. So, high HTHS is good, low NOACK is good. The top two oils here are pao/ester, the 2nd division are pao only and the bottom of the league are blended oils hydrocracked/poa etc. I hope this gives some insight into the hype and the "real thing". Cheers Simon

[clipping_point]

Great stuff!! Thanks, time for an oil change!

[Mutt & Jeff]

Very interesting.......so what do you use? What oil would you reccomend on a protection Vrs. cost basis?.....I currently use Millers Fully Synthetic BTW I'd value your opinion?

[oilman]

My personal favorites for money vrs quality are Silkolene Pro S range or the Motul 300v. Cheers Simon.

[oblomov]

Thanks for taking the trouble to post all that for us Simon I was aware of the importance of shear stability in oil, but nothing more than that, so this is really a great help in deciding what oil to use. Obviously it's fairly crucial in a high performance engine with longer service intervals, like the VXT, and of course to a lesser degree in the NA

[oilman]

No problems, happy to help wherever I can. How about a group buy on some of the decent stuff then? I'm sure if there is enough interest we can sort out some decent prices for members. Cheers Simon