oilman

iTrader: (9)

That's correct, it's all down to basestocks and synthetics are far more stable than petroleum ones.

Here are descriptions of basestocks:

“HYDROCRACKED” (HC) or MOLECULARLY CONVERTED (MC) BASESTOCKS



There are many petroleum oils available on the market that are so pure and refined, they can now be passed off as synthetics.


They are not made from true synthetic basestocks (at least not in the way that synthetics have traditionally been defined), but they have so little in common with traditional petroleum basestocks, it is really somewhat silly to classify them as petroleum oils.

Petroleum oil basestocks can be put through a super-extreme refining process called “hydrocracking”. In some cases, as in the case of one particular name-brand "synthetic" oil, these highly refined petroleum basestocks can actually be termed and sold as "synthetic".

It is completely legal for lubricants manufacturers to label these oils as "synthetic".


These are extremely high performance petroleum basestocks, but they are not truly synthetic the way that most people understand the term and will not necessarily perform to the same level as a premium synthetic oil like PAO (poly alfa olefins) or Esters.



Hydrocracking involves changing the actual structure of many of the oil basestock molecules by breaking and fragmenting different molecular structures into far more stable ones. This results in a basestock which has far better thermal and oxidative stability as well as a better ability to maintain proper viscosity through a wide temperature range - when compared to a typical petroleum basestock.



Although contaminants are still present, and these are still petroleum basestocks, contamination is minimal and performance characteristics are high. This process also can turn a wider range of crude oil stock into well-performing petroleum lubricant basestocks.



TYPES OF SYNTHETIC BASESTOCKS



Synthetic basestocks are not all the same. There are few different chemical types that may be used as synthetic basestock fluids. There are only three that are seen commonly in automotive applications:



Polyalphaolefins (PAO's)


These are the most common synthetic basestocks used in the US and in Europe. In fact, many synthetics on the market use PAO basestocks exclusively. PAO's are also called synthesized hydrocarbons and contain absolutely no wax, metals, sulfur or phosphorous. Viscosity indexes for nearly all PAO's are around 150, and they have extremely low pour points (normally below –40 degrees F). Although PAO's are also very thermally stable, there are a couple of drawbacks to using PAO basestocks. One drawback to using PAO's is that they are not as oxidatively stable as other synthetics. But, when properly additized, oxidative stability can be achieved.


Diesters


These synthetic basestocks offer many of the same benefits of PAO's but are more varied in structure. Therefore, their performance characteristics vary more than PAO's do. Nevertheless, if chosen carefully, diesters generally provide better pour points than PAO's (about -60 to -80 degrees F) and are a little more oxidatively stable when properly additized.

Diesters also have very good inherent solvency characteristics which means that not only do they burn cleanly, they also clean out deposits left behind by other lubricants - even without the aid of detergency additives.

They do have one extra benefit though, they are surface-active (electrostatically attracted to metal surfaces), PAO’s are not “polar”, they are “inert”.


Polyolesters


Similar to diesters, but slightly more complex. Greater range of pour points and viscosity indexes than diesters, but some polyolester basestocks will outperform diesters with pour points as low as -90 degrees F and viscosity indexes as high as 160 (without VI additive improvers). They are also “polar”.


Other synthetic basestocks exist but are not nearly as widely used as those above - especially in automotive type applications. Most synthetics on the market will use a single PAO basestock combined with an adequate additive package to provide a medium quality synthetic lubricant. However, PAO basestocks are not all the same. Their final lubricating characteristics depend on the chemical reactions used to create them.



Premium quality synthetics will blend more than one "species" of PAO and/or will blend these PAO basestocks with a certain amount of diester or polyolester in order to create a basestock which combines all of the relative benefits of these different basestocks.



This requires a great deal of experience and expertise. As a result, such basestock blending is rare within the synthetic lubricants industry and only done by very experienced companies. In addition, although such blending creates extremely high quality synthetic oils, they don't come cheap. You get what you pay for!

Hope this helps

Cheers
Simon

micared

So, where do we stand. Several respected people on here whos' knowledge of the workings of the impreza engine are beyond question are still saying that 10/60 is o.k. The same people are still saying that oil viscosities of 0 or 5 whatever are unacceptable, and seem to have evidence to back this up. Can someone show ANY evidence of an impreza that has had to undergo repair due to the use of 10/60. If not, why continue to call its use into question? Genuinely interested to hear from anyone with a story to tell on this subject.

TonyBurns

iTrader: (3)

Put it this way, Subaru, the manufacturer who test with lots of cash, and design these engines, state (even in japanese i understand this, and in english its plain) that you SHOULD NOT use a 5w30 rated oil in a turbocharged engined car with temps above 0 deg C, and if you do use said oil below 0 deg C, you should not use excessive revs whilst running this oil.
Hey, who are we to argue with Subaru, lots of testing on these engines and its also in the owner handbooks if you look
So, fact, subaru do not rate the 5 rated oils for turbocharged engines, but you can use it in the n/a cars without problems.

Tony

oilman

iTrader: (9)

As a rule of thumb, based on the recommended viscosities I posted on page 1 of this thread from three eminent companies who obtain their data from the Manufacturer direct, I would say...........

All cars pre 2001 should be using 10w-40 or 10w-50. (Perhaps 15w-50 in extreme cases)

On all cars 2001 onwards use 5w-40 or 10w-40 (Perhaps 10w-50 or 15w-50 in extreme cases)

Read what I've posted on page 1 here before deciding though as the recommendations I have made are as I said before taken from Manufacturers data and not just made up.

If anyone wants a FULL lubricants report for their car then just drop me an email referring to "a full lubricants report required" and give the model/year/engine size and I'll email you a full report from the database.

Cheers
Simon

oilman

iTrader: (9)

FYI, here is an example of a FULL lubricants report:

Subaru Impreza 2.0i WRX/STi Turbo 4WD (2001 onwards)

Engine: SL/SJ/A1 5W-30/5W-40 4.5litres
Manual Gearbox: GL-5 75W-90 4.1litres
Auto Gearbox: n/a
Differential(s): GL-5 75W-90 1litre
Coolant: AS 7.7litres
Power Steering (where fitted): ATF-D2
Brake Fluid: DOT 3/4
Wheel Bearings: GrLi2

Cheers
Simon

TonyBurns

iTrader: (3)

Well thats contary to what Subaru state in their documentation, which i will be using as thats what they have tested with, the basic oil stated for turbocharged engines is a 10w40 semi synthetic, this is the MINIMUM oil to be used (also states this in my MY03 STi documentation btw).

Tony

oilman

iTrader: (9)

I think that you'll find that 10w-40 semi-synthetic minimum is a reference to the quality (minimum) as this is not a synthetic oil.

Minimums are stated to protect the Manufacturer, it does not prevent you from using a better oil.

Obviously, if you choose to use the minimum recommended oil (10w-40 semi-synthetic) then you are in the clear if anything goes wrong. Is there any reference to 10w-60 in the handbook?

Cheers
Simon

micared

Are there any references in the history of Scoobynet to 10/60 with regard to engine failure. Think I already know the answer to this. Plenty with regard to 0 or 5/40 though.

Gear Head

iTrader: (2)

Why doesn't someone start a poll.
All different grades listed against people who have had engne failures whilst running that particular oil?? It would sort out this disagreement

micared

Not as clear cut as that unfortunately. We've had the people who've categorically stated that 0 or 5/40 has caused a problem, what we're waiting for is someone to tell us about their problems with 10/60. This thread and all others seem to be spectacularly devoid of such people. What needs to be ascertained is why. And what is the reason behind people calling its abilities into question. Am I the only person to think that it's strange for something to be criticised when it appears that there is no evidence to support it.
To be fair, how does anyone know that any given viscosity/brand of oil is responsible for engine failure, given the inherent weaknesses of the Subaru engine. They self destruct for a multitude of reasons, and it's not always apparent as to why. However, holding 10/60 up for specific scrutiny seems unreasonable, given its lack of negative history on here.
Oilman, do you have anything specific, other than resorting to the handbook argument to support your assertion that Castrol RS 10/60 is potentially problematic, i.e, examples of owners who've suffered from its use? This is specific to Subarus.

Bob Rawle

Since thinner oil rotates through the oil system more quickly then of course it should run a little cooler, thats obvious however its not how hot it gets but how well the oil film withstands stress, thinner oils tend to be worse in this respect, in testing the Motul and Castrol there are NO differences in oil temps that I noted.

FWIW I'm currently running with a Silkolene oil in the STi5 (not Pro S) but I'm only using it for running in purposes.

micared

Bob, in your opinion, are there any downsides to running RS10/60 in a uk MY00 modified to 270 brake approx? The car isn't used on track, but is driven hard on the road.

oilman

iTrader: (9)

This is perhaps the most sensible statement on this debate so far.

Please read my posts, I'm not an engineer, I'm an Oilman and that's my field and expertise.

I have NEVER advocated that 10w-60 or any oil for that matter has caused engine failures, it's rare in fact unless there isn't any oil or someone has done something completely negligent. Engines fail mostly due to weaknesses, component failure or neglect.

What I have been saying though, to cut a long story short is that 10w-60 is too far "out of grade" in my opinion and according to the data that I have is not recommended by the Manufacturer.

That doesn't mean you can't use it or any other oil you choose to but I'm bound as a professional to quote the correct oils to use and not the ones that "must be ok because other people use them!".

We need to get away from these emotive arguments to have a reasonable and informative discussion here. I've provided raw data that is based on fact and technical data written by Chemists etc, you don't have to read it or take notice of it but I would highly suggest that you investigate what I'm saying more closely, you'll find it to be factually and technically correct.

Cheers
Simon

micared

Oilman, I know you've taken some flak over the stuff you post, and it's not my intention to add to it. All I'd like to know, as conclusively as possible, is whether my choice of oil is significantly more likely to cause me a problem in the near or distant future. On the evidence provided so far, I can't see any reason to change. Doesn't mean I don't appreciate your input though! Not often I'm referred to as sensible either, btw.

oilman

iTrader: (9)

In the short term probably not but in the long term, you will experience more wear with thicker oils.

I've posted this advice before but it's worth putting it up again as it's extremely important to understand why I've said what I've said.

Surely the thicker the oil the better!



This isn't always true - even when using a petroleum oil. Although it is true that heavier viscosity oils (which are generally thought of as being thicker) will hold up better under heavy loads and high temperatures, this doesn't necessarily make them a better choice for all applications.


On many newer vehicles only 0w-40, 5w40 or 10w40 engine oils are recommended by the manufacturer. If you choose to use a higher viscosity oil than what is recommended, at the very least you are likely to reduce performance of the engine. Fuel economy will likely go down and engine performance will drop.

In the winter months it is highly recommended that you not use a heavier grade oil than what is recommended by the manufacturer. In cold start conditions you will be causing more engine wear than when using a lighter viscosity oil.

In the summer months, going to a heavier grade is less of an issue, but there are still some things to be aware of.


Moving one grade up from the recommended viscosity is not likely to cause any problems (say from a 10w40 to a 10w50 oil). The differences in pumping and flow resitance will be slight. Although, efficiency of the engine will decrease, the oil will likely still flow adequately through the engine to maintain proper protection. However, it will not likely protect any better than the lighter weight oil recommended by the manufacturer.


Moving two grades up from the recommended viscosity (say 10w40 to 10w-60) is a little more extreme and can cause long term engine damage if not short term.

Although the oil will still probably flow ok through the engine, it is a heavier visocosity oil. As such it will be more difficult to pump the oil through the engine. More friction will be present than with a lighter viscosity oil. More friction means more heat.

In other words, by going to a thicker oil in the summer months, you may actually be causing more heat build-up within the engine. You'll still be providing adequate protection from metal to metal contact in the engine by going with a high viscosity, but the higher viscosity will raise engine temperatures.

In the short run, this is no big deal. However, over the long term, when engine components are run at higher temperatures, they WILL wear out more quickly.

If you intend on keeping the vehicle for awhile, keep this in mind if you're considering using a heavier weight oil than the manufacturer recommends.
The best advice is to is to stay away from viscosity grades that are not mentioned in your owner's manual.



I don't mind taking flak, I just wish that more people understood the fundementals of lubrication before commenting. Oil is a complex issue and using the correct one is important if you wish to protect your pride and joy.

May I remind people of this important article that I posted written by a man that has forgotten more then I know. It's informative and totally factual.

http://bbs.scoobynet.co.uk/showthrea...ht=lubricating

Hope this helps, if not "I'll get me coat".

Cheers
Simon

SoNiCa

I was using Mobil 1 10W-40 Semi Syntc on my car since 45.000 miles without any problems but today I changed it to Shell 10w-60 Ultra Performance with the insistent recommendations of the subaru dealer. In my country, there is no motul or silicone. Furthermore it is impossible to find any fully syntc. oil at 10w40 grade.

vulnax999

iTrader: (7)

I am sure you can get the right oil mailed in, try ASPerformance, they supplied me Motul 300v 10-40.. bu post.

SoNiCa

I think I'll contunie with Shell 10-60W Ultra. Oil pressure reading are really good. 85psi @ 2000 rpm and it is interesting that the odd flickering of the defi gauge went off.

Bob Rawle

There is no noticable difference in oil temps between the two, either of the two I mentioned plus Mobil Motorsport 15:50 would be my first choices, Silkolene Pro S or Pro R as second choice although nether of these maintain consistent pressure with time falling off quite quickly after 3000 miles.

Whatever the ambient temps I would not use a 0-40 or 5-40 in a modified car, Subaru do suggest 5-30 or 5-40 for std cars and use, they specifically state that these are NOT suitable for "heavy" use. Its in the owners manual.

bob

bob

Bob Rawle

BTW the Shell 10-60 is a race oil, not tried it yet but plan to.

bob

oilman

iTrader: (9)

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

pauld37

Heres a question Simon, I drive an my01 wrx, dont really drive it too hard , what would you suggest putting in it

thanks Paul

oilman

iTrader: (9)

You'll find my recommendations here.

http://bbs.scoobynet.co.uk/showthrea...=378713&page=1

Hope this helps,

Cheers
Simon

jmk

At my last oil change (03 WRX PPP) I opted for Silkolene PRO S 10w-50 and since then the tappets seem to be noisier and the noise seems to last for longer after start up. Is this just coincidence (age of car perhaps, engine more 'loose') or more likely because of the oil - previously used Castrol RS 10w-60. The tappets are silent after possibly 15 mins.

pauld37

Cheers Simon