What Oil do you use?

[oilman]

To expand upon what I said above, those who find the subject of oils interesting will find this very interesting reading.

Building a good oil.

It is impossible to make a good 5w-40 or even 10w-40, using only mineral oil. The base oil is so thin, it just evaporates away at the high temperatures found in a powerful engine that is being used seriously. Although there are chemical compounds in there to prevent oil breakdown by oxygen in the atmosphere (oxidation) they cannot adequately protect vulnerable mineral oil at the 130 degC plus sump temperatures found in a hard working turbocharged or re-mapped engine.

The answer to this is synthetics. They are built up from simple chemical units, brick by brick so as to speak; to make an architect designed oil with properties to suit the demands of a modern engine.

The synthetic myth

The word "synthetic" once meant the brick by brick chemical building of a designer oil but the waters were muddied by a court case that took place in the USA some years ago. The outcome was that the right to call heavily modified mineral oil "synthetic" was won. This was the marketing executives dream; the chance to use the word "synthetic" on a can of oil without spending much extra on the contents!

Most lower-cost "synthetic" or "semi-synthetic" oils use these "hydrocracked" mineral oils. They do have some advantages, particularly in commercial diesel lubricants but their value in performance engines is marginal.

TRUE synthetics are expensive and in basic terms there are three broad catagories, each containing many types and viscocity grades:-

PIB's (Polyisobutanes)

These are occasionally used as thickeners in motor oils and gear oils, but their main application is to suppress smoke in two-strokes.

The TWO important ones are:

ESTERS

All jet engines are lubricated with synthetic "esters" and have been for more than 50 years but these expensive fluids only started to appear in petrol engine oils around 20 years ago.
Thanks to their aviation origins, the types suitable for lubricants work well from
-50 degC to 200 degC, and they have an added benefit. Due to their structure, "ester" molecules are "polar"; they stick to metal surfaces using electrostatic forces. This means that a protective layer is there at all times, even during that crucial start-up period. This helps to protect cams, gears, piston rings and valve train components, where lubrication is "boundary" rather than "hydrodynamic", i.e. a very thin non pressure-fed film has to hold the surfaces apart.
Even crank bearings benefit at starts, stops, or when extreme shock loads upset the "hydrodynamic" film.

Synthetic Hydrocarbons or PAO's (Poly Alpha Olefins)

These are, in effect, very precisely made equivalents to the most desirable mineral oil molecules. As with "esters" they work very well at low temperatures and equally well at high temperatures, if protected by anti-oxidants. The difference is, they are inert and not polar. In fact, on their own they are hopeless "boundary" lubricants, with less load carrying ability than a mineral oil. They depend entirely on the correct chemical enhancements.

It is a fact that "PAO's" work best in combination with "esters". The "esters" assist load carrying, reduce friction and cut down seal drag and wear, whilst the "PAO's" act as solvents for the multigrade polymers and a large assortment of special compounds that act as dispersants, detergents, anti-wear and anti-oxidant agents, and foam suppressants.
Both are very good at resisting high-temperature evaporation, and the "esters" in particular will never carbonise in turbo bearings even when provoked by anti-lag systems.

So, in conclusion, Ester gives the best protection and Ester/PAO combinations have great benefits because they work well together. They are more expensive but worth it if you wish to do the best for your engine.

Cheers
Simon

 

[John Sims]

Thanks for that Simon.

Can you confirm if the likes of Castrol RS and Mobil 1 are "true" synthetics or are they "synthetics" by the American standard. For the price I would hope the are the real thing, but marketing can give many products a price way above their true value.

 

[ClubSport 911]

three very different types of engine, the 8 valvers, the Turbos, and the 16 valvers

What about the "12 valvers" ?[]

 

[edh]

I've just started using Millers 10w60 competition oil (£21 for 5 litres at trade price )

- my 924S is quite long in the tooth & had very low oil pressure (using 15w40 mineral) after about 20 mins at Donington (falling below 3 bar at 4k rpm!)

The Millers seems to handle the heat much better - on my last track day the pressures stayed higher (and recovered faster)

 

[oilman]

ORIGINAL: John Sims

Thanks for that Simon.

Can you confirm if the likes of Castrol RS and Mobil 1 are "true" synthetics or are they "synthetics" by the American standard. For the price I would hope the are the real thing, but marketing can give many products a price way above their true value.

They are PAO's but vary in composition. Unfortunately the American Court Case changed things and as most manufacturers are reluctant to post the compositional information the only way to tell is lab reports which are difficult to get hold of and expensive to conduct.

Here's more on the Court Case which explains how the market is since.

It was all sorted in a legal battle that took place in the USA about ten years ago. Sound reasons (including evidence from a Nobel Prize winning chemist) were disregarded and the final ruling was that certain mineral bases that had undergone extra chemical treatments could be called "synthetic". Needless to say, the marketing executives wet their knickers with pure delight! They realised that this meant, and still does, that the critical buzz-word "synthetic" could be printed on a can of cheap oil provided that the contents included a few percent of "hydrocracked" mineral oil, at a cost of quite literally a few pence.

So, the chemistry of "synthetics" is complex and so is the politics!

The economics are very simple. If you like the look of a smart well-marketed can with "synthetic" printed on it, fair enough, it will not cost you a lot; and now you know why this is the case. But, if you drive a high performance car, and you intend to keep it for several years, and maybe do the odd "track day", then you need a genuine Ester/PAO (Poly Alpha Olefin) synthetic oil. This oil costs more money to buy, because it costs a lot of money to make, very simply, you always get what you pay for!

The above is quoted from an article written by John Rowland (Chief Chemist, Silkolene) who has been on the Chemistry side of the Oil Business for more than 40 Years.

Hope this helps

Cheers
Simon

 

[oilman]

Bump

 

[John Sims]

Bump

Don't be cheeky or I'll delete the thread.

Obviously there isn't any self promotion going off here is there?

I'm starting to get into this moderating lark now.[]

 

[oilman]

John,

I'm sorry I'm not trying to promote anything other than the excellent advice of a very experienced R&D Chemist of 40 years.

To put in context the snippets above, I'll post the full article here. It's long, not written by a salesman and both informative and factual - It's worth the read.

In case anyone thinks its on the wrong forum, delete Subaru and add any high powered, re-mapped or modded car, the theory and advice applies to all.

I do not work for Silkolene and I have the authors express permission to post this article to clear up as he would term "the mis-information" on the internet.

Lubricating the Subaru. (or any high powered, re-mapped or modded car)

Basically

Basically, to use that irritating in-word, engine lubrication is simple, and consequently boring. So I intend to treat the subject "complicatedly", which may not be an in-word, but makes life far more interesting!

So, to take a quick look at the simple picture; the oil keeps moving parts apart, reducing friction and carrying away heat. Where there is metal-to-metal contact there are chemicals in the oil to reduce damage. Because the internal combustion process is always less than perfect, some soot is produced and this must be washed off the pistons and rings by the oil, so it has a cleaning or detergent function as well.

The trouble is, all this is just as true for Henry Ford's original Model T engine as it is for the Subaru or any other high output motor. So where is the difference? The Model T, with 10bhp/litre at 2,000rpm and a single underhead camshaft, was filled with a thick, greenish liquid from somewhere near the bottom of the distillation colums on the Pennsylvania oilfields. It did a vague tour of the internals by guesswork (there was no oil pump) at a temperature around 50 degC, and lasted for 1,000 miles. On the plus side, some of the impurities acted as anti-wear and detergent chemicals. They didn't work very well, but it was better than nothing. The engine wore out in around 20,000 miles, but even ordinary people, not just amateur rally drivers, were happy to put up with this.

The difference begins with the first turn of the key. The modern high-pressure pump would cavitate on the old heavy monogrades, starving the bearings for a vital couple of seconds, even in warm weather. Likewise, cam lobes would suffer as the sluggish oil found its way along narrow oil ways to the valve gear. The turbo bearing (if fitted as the handbooks say) already spinning fast, would also starve, and when it got going, how long would it be before the heat soak-back fried the primitive oil into a lump of carbon? (This was the problem with "modern" oils only 15 years ago).

So, a good oil must be quite low in viscosity even in the cold, so that it gets around the engine in a fraction of a second on start-up. On the other hand, it must protect engine components (piston rings for example) at temperatures up to 300 degC without evaporating or carbonising, and maintain oil pressure.

Unmodified thin oils simply can't manage this balancing act. The answer is to use a mixture of thin oil and temperature-sensitive polymer, so as the thin oil gets even thinner with increasing temperatures as the engine warms up, the polymer expands and fights back, keeping the viscosity at a reasonable level to hold oil pressure and film thickness on the bearings. This is called a multigrade.

But, this is all too basic! What I have just written was and is relevant to a 1958 Morris Minor.

The questions that Subaru owners need to ask are: "Will this thin oil evaporate and be drawn into the intake manifold (via the closed circuit crankcase ventilation), leading to combustion chamber deposits and de-activated catalysts?" and "Will the polymer shear down at high engine revolutions and high temperatures, causing low oil pressure and component wear?" and "Will it carbonise on the turbo bearing?" These are 21st century questions which cannot be answered by a basic 1990's approach.

BUT! Before we head into more complications, some figures"¦"¦"¦

The SAE Business (American Society of Automotive Engineers)

Viscosity is the force required to shear the oil at a certain speed and temperature. Oils work because they have viscosity; the drag of a rotating part pulls oil from a low-pressure area into a high pressure area and "floats" the surfaces apart. This is called "hydrodynamic lubrication", and crank bearings depend on it. In fact a plain bearing running properly shows literally no metal-to-metal contact. Experimental set-ups have shown that electrical current will not flow from a crank main bearing to the shells. Also, the energy loss due to friction (the co-efficient of friction) is incredibly low, around 0.001. So for every kilogram pulling one way, friction fights back with one gram. This is very much better than any "dry" situation. For example, the much over-rated plastic PTFE has a co-efficient of friction on steel of 0.1, 100 times worse than oil.

Oil viscosities are accurately measured in units called "Centistokes" at exactly 100 degC. These fall into five high temperature SAE catagories:-

SAE No. 20 30 40 50 60
Viscosity Range 5.6 - <9.3 9.3 - <12.5 12.5 - <16.3 16.3 - <21.9 21.9 - <26

A decent quality oil usually has a viscosity that falls in the middle of the spec, so a SAE 40 will be about 14 Centistoke units, but SAE ratings are quite wide, so it's possible for one 40 oil to be noticeably thicker or thinner than another.

When the polymer modified multigrades appeared, a low temperature range of tests were brought in, called "W" for winter (it doesn't mean weight). These simulate cold starta at different non-ferrous monkey endangering temperatures from ""15 degC for the 20w test to a desperate ""35 degC for 0w. So, for example, an SAE 5w-40 oil is one that has a viscosity of less than 6600 units at ""30 degC, and a viscosity of about 14 units at 100 degC.

Now, those of you who have been paying attention will say "Just a minute! I thought you said these multigrade polymers stopped the oil thinning down, but 6600 to 14 looks like a lot of thinning to me!". Good point, but the oil does flow enough to allow a marginal start at ""30 degC, and 14 is plenty of viscosity when the engine is running normally. (A lot more could damage the engine. Nobody uses the 24 viscosity SAE 60 oils any more.) The vital point is, a monograde 40 would be just like candle wax at ""30 degC, and not much better at ""10 degC. It would even give the starter motor a fairly difficult time at 0 degC. (At 0 degC, a 5w-40 has a viscosity of 800 but the monograde 40 is up at 3200!)

Another basic point about wide ranging multigrades such as 5w-40 or 0w-40 is that they save fuel at cruising speeds, and release more power at full throttle. But complications arise"¦"¦..

Building a good oil

A cave may not be the best place to live, but it's ready-made and cheap. This is the estate agent's equivalent of an old style monograde oil. Or you could get Hengist Pod to fit a window and a door; this is moving up to a cheap and cheerful mineral 20w-50. But an architect-designed "machine for living in", built up brick by brick, is an allegory of a high performance synthetic oil.

It is impossible to make a good 5w-40, or even 10w-40, using only mineral oil. The base oil is so thin, it just evaporates away at the high temperatures found in a powerful engine that is being used seriously. Although there are chemical compounds in there to prevent oil breakdown by oxygen in the atmosphere (oxidation) they cannot adequately protect vulnerable mineral oil at the 130 degC plus sump temperatures found in hard worked turbocharged or re-mapped engines.

Synthetics are the answer. They are built up from simple chemical units, brick by brick so as to speak; to make an architect-designed oil with properties to suit the modern engine.

But sometimes, if you look behind the façade, there is a nurky old cave at the back! This is because the marketing men have been meddling!

The Synthetic Myth

What do we mean by the word "synthetic"? Once, it meant the "brick by brick" chemical building of a designer oil, but the waters have been muddied by a court case that took place in the USA a few years ago, where the right to call heavily-modified mineral oil "synthetic", was won. This was the answer to the ad-man's dream; the chance to use that sexy word "synthetic" on the can"¦.without spending much extra on the contents! Most lower cost "synthetic" or "semi-synthetic" oils use these hydrocracked mineral oils. They do have some advantages, particularly in commercial diesel lubricants, but their value in performance engines is marginal.

TRUE synthetics are expensive (about 6 times more than top quality mineral oils). Looked at non-basically there are three broad catagories, each containing dozens of types and viscosity grades:-

PIB's (Polyisobutanes)

These are occasionally used as thickeners in motor oils and gear oils, but their main application is to suppress smoke in 2-strokes.

The two important ones are:

Esters

All jet engines are lubricated with synthetic esters, and have been for 50 years, but these expensive fluids only started to appear in petrol engine oils about 20 years ago. Thanks to their aviation origins, the types suitable for lubricants (esters also appear in perfumes; they are different!) work well from ""50 degC to 200 degC, and they have a useful extra trick.
Due to their structure, ester molecules are "polar"; they stick to metal surfaces using electrostatic forces. This means that a protective layer is there at all times, even during that crucial start-up period. This helps to protect cams, gears, piston rings and valve train components, where lubrication is "boundary" rather than "hydrodynamic", i.e. a very thin non-pressure fed film has to hold the surface apart. Even crank bearings benefit at starts, stops or when extreme shock loads upset the "hydrodynamic" film. (Are you listening, all you rally drivers and off road fanatics?)

Synthetic Hydrocarbons or POA's (Poly Alpha Olefins)

These are, in effect, very precisely made equivalents to the most desirable mineral oil molecules. As with esters, they work very well at low temperatures, and equally well when the heat is on, if protected by anti-oxidants. The difference is, they are inert, and not polar. In fact, on their own they are hopeless "boundary" lubricants, with LESS load carrying ability than a mineral oil. They depend entirely on the correct chemical enhancements.

PAO's work best in combination with esters. The esters assist load carrying, reduce friction, and cut down seal drag and wear, whilst the PAO's act as solvents for the multigrade polymers and a large assortment of special compounds that act as dispersants, detergents, anti-wear and oxidant agents, and foam suppressants. Both are very good at resisting high-temperature evaporation, and the esters in particular will never carbonise in turbo bearings even when provoked by anti-lag systems.

Must Have MORE Power!

Motorcars are bought for all sorts of reasons, but enthusiasts like lots of power. To get more power, a lot of fuel must be burnt, and more than half of it, sadly, gets thrown away as waste heat. For every litre of fuel burnt, 60% of the energy goes as waste heat into the exhaust and cooling system. A turbocharger can extract a few percent as useful energy and convert it into pressure on the intake side, but only 40-45% is left, and only 25% actually shows up as BHP at the flywheel. 6% goes in pumping air into the engine, 6% as oil drag losses and 2-3% as engine friction. The oil deals with 97% of the friction; so reducing the remaining few percent is not easy. If you doubt that even ordinary oil has a massive effect, take a clean, dry 200 bhp engine, connect it to a dyno and start it up. It will only make 1 bhp for a few seconds. Now that's real friction for you!

Oddly enough, people get starry-eyed about reducing friction, especially those half-wits who peddle silly "magic additives", which have not the smallest effect on friction but rapidly corrode bearings and wallet contents. In fact, even a virtually impossible 50% reduction in the remaining engine friction would be no big deal, perhaps one or two bhp or a couple of extra miles per gallon.

Even More Power!

He place to look for extra power is in that 6% lost as oil drag. In a well-designed modern motor, the oil doesn't have to cover up for wide clearances, poor oil pump capacity or flexy crankshafts, so it can be quite thin. How thin? Well take a look at these dyno results.

A while ago now, we ran three Silkolene performance oils in a Honda Blackbird motorcycle. this fearsome device is fitted with a light, compact, naturally aspirated 1100cc engine which turns out 120+ bhp at the back wheel. The normal fill for this one-year-old engine was 15w-50, so the first reading was taken using a fresh sump-fill of this grade. (The dyno was set up for EEC horsepower, i.e. Pessimistic)

15w-50
Max Power 127.9 bhp @ 9750 rpm
Torque 75.8 ft-lbs @ 7300 rpm

After a flush-out and fill up with 5w-40 the readings were;

5w-40
Max Power 131.6 bhp @ 9750 rpm
Torque 77.7 ft-lbs @ 7400 rpm

Then we tried an experimental grade, 0w-20 yes, 0w-20! This wasn't as risky as you may think, because this grade had already done a season's racing with the Kawasaki World Superbike Team, giving them some useful extra power with no reliability problems. (But it must be said, they were only interested in 200 frantic miles before the engines went back to Japan)

0w-20
Max Power 134.4 bhp @ 9750 rpm
Torque 78.9 ft-lbs @ 7400 rpm

In other words, 3.7 bhp / 2.9% increase from 15w-50 to 5w-40, a 2.8 bhp / 2.1% increase from 5w-40 to 0w-20 or a 6.5 bhp / 5% overall. Not bad, just for changing the oil! More to the point, a keen bike owner would have paid at least £1000 to see less improvement than this using the conventional approach of exhaust/intake mods, ignition re-mapping etc.

Am I recommending that you use 0w-20 in your Subaru's? Well, perhaps not! The 5w-40, which is a "proper" PAO/Ester shear-stable synthetic, will look after a powerful engine better than a heavier viscosity "cave at the back" conventional oil, and provide a useful extra few BHP.

The End

However, as with all good things in life, we don't live in a world of perfect motor cars and therefore we have to look at the lubrication trade-off between longevity, reliability, power and cost, relative to the vehicle in which the oil is being used (a scruffy old XR2i with 192,000 miles on the clockis a very different proposition to your spanking new Impreza). Which is why Subaru (and probably your local dealer) recommends a 10w-50 (Such as PRO S); you could look at a 5w-40 for competition and track-day use, but only the most committed competitor would want, or need, the 0w-20 for the extra 5% power.

Cheers
Simon

 

[944Turbo]

Ok I have decided to try some silkoline oil, would you reccomend pro R or Pro S for a 1990 944 turbo driven hard, 6,000 mile oil changes, some trackday use, currently using Mobil1 motorsport, only occasional short journeys. Near the South coaast so hardly any days below -5C
Table earlier in topic from my handbook thanks,
Tony

 

[oilman]

To be honest you could use either PRO R 15w-50 or PRO S 10w-50 but there will be more benefits on cold start and short journeys in using the 10w-50 so this would be my first choice.

Cheers
Simon

 

[944Turbo]

Thanks, just looking at the data sheets, whats the diference between API SH/SJ, CCMC G4 and API SJ/SL, CF CCMC G5?
Tony

 

[oilman]

Here they are:

API = American Petroleum Institute
S = Service - Petrol Engine Performance
C = Commercial - Diesel Engine Performance

PETROL

SG - Introduced 1989 has much more active dispersant to combat black sludge.

SH - Introduced 1993 has same engine tests as SG, but includes phosphorus limit 0.12%, together with control of foam, volatility and shear stability.

SJ - Introduced 1996 has the same engine tests as SG/SH, but phosphorus limit 0.10% together with variation on volatility limits

SL - Introduced 2001, all new engine tests reflective of modern engine designs meeting current emmissions standards

DIESEL

CD - Introduced 1955, international standard for turbo diesel engine oils for many years, uses single cylinder test engine only

CE - Introduced 1984, improved control of oil consumption, oil thickening, piston deposits an wear, uses additional multi cylinder test engines

CF4 - Introduced 1990, further improvements in control of oil consumption and piston deposits, uses low emmission test engine

CF - Introduced 1994, modernised version of CD, reverts to single cylinder low emission test engine. Intended for certain indirect injection engines

CF2 - Introduced 1994, defines effective control of cylinder deposits and ring face scuffing, intended for 2 stroke diesel engines

CG4 - Introduced 1994, development of CF4 giving improved control of piston deposits, wear, oxidation stability and soot entrainment. Uses low sulphur diesel fuel in engine tests

CH4 - Introduced 1998, development of CG4, giving further improvements in control of soot related wear and piston deposits, uses more comprehensive engine test program to include low and high sulphur fuelsSG - Introduced 1989 has much more active dispersant to combat black sludge.

Cheers
Simon

 

[paulf968]

We are all learning some stuff here.

Having got this far in this thread -- do I qualify for some sort of Doctorate in oil technology? That would be nice.


paul f

 

[944Turbo]

Last question, probably [], but was does the phosphorus do, is it nasty to the engine health or is it good for engines but nasty to humans - like lead in petrol?
Tony

 

[944Turbo]

In an attempt to answer my question, I did some more research and found thislink which would seem to indicate phosphorous helps to prevent wear, but is hazardous to catalytic convertors (different article). As I no longer have a cat and live in the warm south (hardly ever -10 and when it is I will probably drive the 4x4) I am now tending towards the Pro R. Other than on very cold mornings will it offer the same protection or is it designed to be changed more frequently?
Thanks,
Tony

 

[oilman]

Sorry for not replying sooner but I missed this one.

Phosphorus in engine oil is in a class of compounds called ZDDPs, zinc di-alkyl di-thio phosphates. These oil-soluble zinc/sulphur/phosphorus/hydrocarbon compounds have been used in lubricating oil for over 50 years.

They help to prevent a sludge-forming reaction between oil and oxygen (oxidation) thus extending the life of the oil. At the same time, they reduce wear. The sulphur and phosphorus in ZDDP react with ferrous metal surfaces at high temperatures and pressures to produce wear-resisting (but non-corrosive) layers. They even improve the anti-rust properties of the oil.

In modern engines very little of the oil is burnt, but the very small amounts of phosphorus compounds released when burnt oil escapes into the exhaust can reduce catalyst efficiency over a long period of time.

Because of this very high levels of ZDDP are avoided in modern lubricants

Pro R and Pro S are virtually the same apart from their viscocities.

Cheers
Simon

 

[Veerzigzag]

Suggest RTFM - page 110 to be precise.

 

[944 man]

Whilst every owner should read their manual, it isnt necessarily the best place for oil advice now, thirty years after they were built.

 

[TTM]

ORIGINAL: julianjwt
Is 10/40 the best for a 86 Turbo?

I would use a 15W50.

 

[944 man]

I will add, that Id also try to use the best synthetic that I can. The '944 synthetic oil problem' has little to do with the oils origin and everything to do with grade.