I've been using Mobil 15w40 in my '88 928s4. Previously Castrol GTX 20w50 was used by PO. I used Mobil because think that Mobil
has a very good reputation. No fancy evaluation, I know.

Viscosity (20w50) is measured in units called "weight". The "w" indicates a "winter" qualified multigrade oil. The 20 is a measure
of the amount of flow at low temp, as the 50 indicates the amount at high temp. A lower viscosity rate means thinner, and more flow.
It is like "less resistance to flow". The 20w50 equals the flow of a single-weight 20 oil at low temp, and a single-50 weight when hot in a 20w50 multigrade oil. Modern oils try to stabilize the viscosity on a level 20wt~5w30, 35wt~15w50 throughout the entire temperature range (0wt-60wt). This is done by choosing a certain mixture of components.

Dino type oil:
=========
>>Pros: cheap and decent quality available. Should however preferably
              not be mixed with other brands. Use a multigrade oil 15w40 or 15w50.
              Porsche says API/SE in older, and API/SJ spec in the newer 928. API/SJ-CF
              should be the minimum, which never seems to be a problem to find.
>>Cons: not the best on the market, especially in high temp fluctuation
              environment. It is known to leave buildup's on the seals.

Half/Semi synthetic blend:
=================
>>Pros: fairly cheap, and better quality than Dino. Available from almost
             any shop, gas station etc. Can still be mixed with same Brand-dino oil
             whenever required (to top up). Mobil 1 is one of them. The new Mobil 1
             seems to "pour" even better at low temps than a full synthetic.
             20% synthetic/80% dino mix is commonly used. This ability to mix oil is
             one of the criteria to pass the API certification. If money is an issue,
             this is a fair deal. But for a few bucks more take a full-synthetic oil.
             Some say that the semi-synth has the same effect as a full synth. It
             eventually also cleans out the crud in the engine.
>>Cons: Kind a expensive for a 20/80 blend. You might mix them yourself
             by using the oil of same brand. At least you know what's in there.

Full synthetic oil:
===========
>>Pros: premium performance at low and high temps, clean engine, no build up
             of residue because of impurities of the oil. Due to purity of synt.oil it
             can cope with longer intervals between oil changes. Less oil breakdown.
             The engine may or may not leak due to the removal of residue from previous
             Dino oils, and thus making room for more leaks, especially seals and
             gaskets. It is recommended to stay with same brand in order to avoid
             different additives and solvents that have negative effects on seals and
             o-rings. So if your seals are in top condition, you're ok. With bad seals
             the crud may just prevent more leakage, and cleaning out will increase the
             leaking. The older Mobil-1 0w15 is known to un-swell the seals causing leaks,
             but the engineers fixed this by altering the additive package some time ago.
>>Cons: you may reconsider using Synth. when already experiencing leaks and
             want to avoid the chance of more leaking. You can still switch back to
             Dino without big problems but this will not reverse the leaks. Try to stay
             within one brand to avoid other solvents working on the seals. This is one
             of the reasons that full.Synth gets blamed for leaks. The full Synth is
             the most expensive choice.

So the advice: Use a good Synthetic oil (Mobil 1 ?) when the engine seals are in good condition and money is not an issue. Always use oils from the same brand in the engine regardless of Synthetic or Dino.

See also: More Than You Ever Wanted to Know About Motor Oil
http://www.vtr.org/maintain/oil-overview.html

Theo
'88 928s4 cherry red
The Netherlands
http://jenniskens.livedsl.nl

What's all this 10W-40, SG stuff about oils?

sae 15 oil is thin and runny at high temperatures, which is undesirable from lots of other points of view.

so what you really need, is something that's the right consistency (or tries to be) at all temperatures - a multigrade oil. eg, sae 15w50. traditionally it was 20w50, but now 15w50, 10w50 and 10w40 are common. this reflects the fact that modern engines are built to higher tolerances and therefore can run (indeed sometimes run better) on lower viscosity oil.

the 15w50 is meant to behave like sae 15 at some (lowish) temperature and like sae 50 at (approximately) normal engine temperature.

I found personally that a 15w50 was better in the summer (in an air-cooled bike) because the engine gets hotter than usual in the summer, therefore the 10w40 gets a bit thin...tended to result in rough gear changing, in fact, not evident when the engine was cold.

so bearing in mind that summers approaching, I'd say go ahead and use 15w50, unless it says not to in big letters in the manual. the only thing thats likely to happen is that the oils a little bit stiffer on a cold morning, so the bike might be a tad more difficult to start, and if you're paranoid don't thrash it too much with a cold engine (but then we don't, do we?).

the other thing about oil is the quality. here the most common system would appear to be the American petroleum institute (a.p.i.) service classification, this looks summat like SF/CC or SG/CD or summat. basically, crappy oil doesn't quote a quality, cheap but less crappy oil tends to be SE/CC or SF/CC, better oil is probably SG/CD or SG/CE. the 2 sets of letters are petrol/diesel, and they seem to follow a logical progression. the SG oils are claimed to combat build-up of black sludge, which gathers in the cooler parts of engines used for commuting in cars , so not very likely to apply to bikes.

and no I don't know why its w in 15w50 etc....

unless w refers to some temperature values?

does anyone actually know?

eg maybe w means (say) 10C cold, 85C hot or summat?

hohum...more waffle...

Austin.

Could the W stand for weight? You often hear people refer to "15-weight" fork oil, or whatever. Don't see what it's gravitational attractiveness has to do with it though.

Liked Austin's missive, but I'd add a couple of points:

The 15/50 in Halfords is presumably GTX (Castrol are owned by Halfords, I believe). This is primarily a CAR oil. Cars generally run to 7,000 rpm or so, and have separate gearboxes and clutches. Bikes run to at least 10,000 (except Guzzis) and generally use the same oil for engine, gearbox and clutch (again, except Guzzis).

Therefore I prefer to use a bike oil that was (hopefully) designed for use under these conditions, except in the Guzzi, where I use GTX.

Depends how skint you are though, I guess.

Secondly - cold starting: The biggest wear problems occur on the cams. These are at the top of the engine (except on... oh never mind) and therefore 15 weight oil will have a harder job getting up there. This is especially critical on early GPZ900's which have not had the "cam lube mod". A procedure I was recommended to avoid this was: Leave choke off initially. Crank engine for 3-4 seconds on starter. Put choke on and start engine. DO NOT 'blip' the throttle. The non-starting cranking does two things:

1. It gets oil up to the cams before they start moving at speed :-)
2. It makes everyone think your bike's knackered and won't start :-(

 Roger Ford                             Phone : 0932 87 2020 ext 2260

> Paul

I'd guess you have to strike a balance between oil to thin when hot (not enough lubrication) and oil to thick (clutch drag??)

i'm not arguing, just interested btw.

Austin.

> ...Note also that the novel behavior of multi-grade oils is caused
> by additives...

Martyn

Useful info - if a bit American (and long).

Given the comments about 10W40 - I wonder if their measurements are the same as ours?

Regards,

Roger Ford                             Phone : 0932 87 2020 ext 2260

Motor Oil Primer

by Ed Hackett

[Ed is a chemical engineer who works for the University of Nevada's Desert Research facility -- Ed.].<edh@maxey.unr.edu>

Edits: v1.0 First there was 1.0.  Before that there was darkness.

 v1.1 Change in description of viscosity. 

v1.2 Updated info on AMSOIL (courtesy of Morgan McArthur <mgn@inel.gov>)

First, I will answer a couple of questions asked by another. Yes, it is OK to mix mineral and synthetic oils. One of the early synthetics used was a polyalkylene glycol. This was totally incompatible and would gel when mixed. This has not been used for years for automotive lubrication. All common synthetics used for engine lubrication nowadays are a poly-alpha-olefin (Mobil 1) or a dibasic organic ester type (AMSOIL). These are fully compatible with conventional oils. In fact Golden Spectro and AGIP Sint 2000 are mixtures of mineral and synthetic oils. It is always best to mix oils with the same rating (SG). This insures that the additive packages are compatible and will maintain their effectiveness.

All engine oils use an organic zinc compound as an extreme pressure/anti wear additive. Spectro adds more to their Motorcycle oil than to the car oil because zinc is a poison to catalytic converters. You will also see that some "car" oil contains more than their motorcycle oil. The difference in zinc content between 0.11% and 0.16% is insignificant to the converter. The little data I saw on the oils packaged by the motorcycle manufacturers indicated that they were no better than the top automotive oils. While most were good, they didn't offer anything the cheaper oils do. (They are in reality just repackaged and in some cases slightly reformulated top grade auto oils).

Choosing the best motor oil is a topic that comes up frequently in discussions between motor heads, whether they are talking about motorcycles or cars. The following article is intended to help you make a choice based on more than the advertizing hype.

Oil companies provide data on their oils most often referred to as "typical inspection data". This is an average of the actual physical and a few common chemical properties of their oils. This information is available to the public through their distributors or by writing or calling the company directly. I have compiled a list of the most popular, premium oils so that a ready comparison can be made. If your favorite oil is not on the list get the data from the distributor and use what I have as a data base.

This article is going to look at six of the most important properties of a motor oil readily available to the public: viscosity, viscosity index (VI), flash point, pour point, percent sulfated ash, and percent zinc.

Viscosity is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develop and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. Thicker oils generally have a higher viscosity, and thinner oils a lower viscosity. This is the most important property for an engine. An oil with too low a viscosity can shear and loose film strength at high temperatures. An oil with too high a viscosity may not pump to the proper parts at low temperatures and the film may tear at high rpm.

The weights given on oils are arbitrary numbers assigned by the SAE. (Society of Automotive Engineers). These numbers correspond to "real" viscosity, as measured by several accepted techniques. These measurements are taken at specific temperatures. Oils that fall into a certain range are designated 5, 10, 20, 30, 40, 50 by the SAE. The W means the oil meets specifications for viscosity at 0 F and is therefore suitable for Winter use.

The following chart shows the relationship of "real" viscosity to their SAE assigned numbers. The relationship of gear oils to engine oils is also shown.

Multi viscosity oils work like this: Polymers are added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. The polymers can shear and burn forming deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that range. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. Very few manufactures recommend 10W-40 any more, and some threaten to void warranties if it is used. It was not included in this article for that reason. 20W-50 has the same 30 point spread, but because it starts with a heavier base, it requires less viscosity index improvers (polymers) to do the job. AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30. Mobil 1 uses no viscosity improvers in their 5W-30, and I assume the new 10W-30. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.

Viscosity index is an empirical number indicating the rate of change in viscosity of an oil within a given temperature range. Higher numbers indicate a low change, lower numbers indicate a relatively large change. The higher the number the better. This is one major property of an oil that keeps your bearings happy. These numbers can only be compared within a viscosity range. It is not an indication of how well the oil resists thermal breakdown.

Flash point is the temperature at which an oil gives off vapors that can be ignited with a flame held over the oil. The lower the flash point the greater tendency for the oil to suffer vaporization loss at high temperatures and to burn off on hot cylinder walls and pistons. The flash point can be an indicator of the quality of the base stock used. The higher the flash point the better. 400 F is the minimum to prevent possible high consumption. Flash point is in degrees F.

Pour point is 5 degrees F above the point at which a chilled oil shows no movement at the surface for 5 seconds when inclined. Pour point is especially important for oils used in the winter. A borderline pumping temperature is given by some manufacturers. This is the temperature at which the oil will pump and maintain adequate oil pressure. This was not given by a lot of the manufacturers, but seems to be about 20 degrees F above the pour point. The lower the pour point the better. Pour point is in degrees F.

Percent sulfated ash is how much solid material is left when the oil burns. A high ash content will tend to form more sludge and deposits in the engine. Low ash content also seems to promote long valve life. Look for oils with a low ash content.

Percent zinc is the amount of zinc used as an extreme pressure, anti-wear additive. The zinc is only used when there is actual metal to metal contact in the engine. Hopefully the oil will do its job and this will rarely occur, but if it does, the zinc compounds react with the metal to prevent scuffing and wear. A level of 0.11% is enough to protect an automobile engine for the extended oil drain interval, under normal use. Those of you with high revving, air cooled motorcycles or turbo charged cars or bikes might want to look at the oils with the higher zinc content. More doesn't give you better protection, it gives you longer protection if the rate of metal to metal contact is abnormally high. High zinc content can lead to deposit formation and plug fouling.

Motor Oil Data

 

Listed alphabetically, data not available indicated by ---



Brand                   V.I.    Flash   Pour    %ash   %zinc

------------------------------------------------------------

20W-50

AMSOIL (old)            136     482     -38     <.5     ---

AMSOIL (new)            157     507     -44     ---     ---

Castrol GTX             122     440     -15     .85     .12

Exxon High Performance  119     419     -13     .70     .11

Havoline Formula 3      125     465     -30     1.0     ---

Kendall GT-1            129     390     -25     1.0     .16

Pennzoil GT Perf.       120     460     -10     .9      ---

Quaker State Dlx.       155     430     -25     .9      ---

Shell Truck Guard       130     450     -15     1.0     .15

Spectro Golden 4        174     440     -35     ---     .15

Spectro Golden M.G.     174     440     -35     ---     .13

Unocal                  121     432     -11     .74     .12

Valvoline All Climate   125     430     -10     1.0     .11

Valvoline Turbo         140     440     -10     .99     .13

Valvoline Race          140     425     -10     1.2     .20

------------------------------------------------------------

20W-40

AMSOIL                  124     450     -49     ---     ---

Castrol Multi-Grade     110     440     -15     .85     .12

Quaker State            121     415     -15     .9      ---

------------------------------------------------------------

15W-50

Chevron                 204     415     -18     .96     .11

Mobil 1                 180     430     -55     ---     ---

Mystic JT8              144     420     -20     1.7     .15

------------------------------------------------------------

15W-40

AMSOIL (old)            135     460     -38     <.5     ---

AMSOIL (new)            164     462     -49     ---     ---

Castrol                 134     415     -15     1.3     .14

Chevron Delo 400        136     421     -27     1.0     ---

Exxon XD3               ---     417     -11     .9      .14

Exxon XD3 Extra         135     399     -11     .95     .13

Kendall GT-1            135     410     -25     1.0     .16

Mystic JT8              142     440     -20     1.7     .15

Shell Rotella w/XLA     146     410     -25     1.0     .13

Valvoline All Fleet     140     ---     -10     1.0     .15

Valvoline Turbo         140     420     -10     .99     .13

------------------------------------------------------------

10W-30

AMSOIL (old)            142     480     -70     <.5     ---

AMSOIL (new)            162     520     -76     ---     ---

Castrol GTX             140     415     -33     .85     .12

Chevron Supreme         150     401     -26     .96     .11

Exxon Superflo Hi Perf  135     392     -22     .70     .11

Exxon Superflo Supreme  133     400     -31     .85     .13

Havoline Formula 3      139     430     -30     1.0     ---

Kendall GT-1            139     390     -25     1.0     .16

Mobil 1                 ---     430     -60     ---     ---

Pennzoil PLZ Turbo      140     410     -27     1.0     ---

Quaker State            156     410     -30     .9      ---

Shell Fire and Ice      155     410     -35     .9      .12

Shell Super 2000        155     410     -35     1.0     .13

Shell Truck Guard       155     405     -35     1.0     .15

Spectro Golden M.G.     175     405     -40     ---     ---

Unocal Super            153     428     -33     .92     .12

Valvoline All Climate   130     410     -26     1.0     .11

Valvoline Turbo         135     410     -26     .99     .13

Valvoline Race          130     410     -26     1.2     .20

------------------------------------------------------------

5W-30

AMSOIL (old)            168     480     -76     <.5     ---

AMSOIL (new)            186     464     -76     ---     ---

Castrol GTX             156     400     -35     .80     .12

Chevron Supreme         202?    354     -46     .96     .11

Exxon Superflow HP      148     392     -22     .70     .11

Havoline Formula 3      158     420     -40     1.0     ---

Mobil 1                 150     430     -65     ---     ---

Mystic JT8              161     390     -25     .95     .1

Quaker State            165     405     -35     .9      ---

Shell Fire and Ice      167     405     -35     .9      .12

Unocal                  151     414     -33     .81     .12

Valvoline All Climate   135     405     -40     1.0     .11

Valvoline Turbo         158     405     -40     .99     .13

------------------------------------------------------------

All of the oils above meet current SG/CD ratings and all vehicle manufacturer's warranty requirements in the proper viscosity. All are "good enough", but those with the better numbers are icing on the cake. The synthetics offer the only truly significant differences, due to their superior high temperature oxidation resistance, high film strength, very low tendency to form deposits, stable viscosity base, and low temperature flow characteristics. Synthetics are superior lubricants compared to traditional petroleum oils. You will have to decide if their high cost is justified in your application.

The extended oil drain intervals given by the vehicle manufacturers (typically 7500 miles) and synthetic oil companies (up to 25,000 miles) are for what is called normal service. Normal service is defined as the engine at normal operating temperature, at highway speeds, and in a dust free environment. Stop and go, city driving, trips of less than 10 miles, or extreme heat or cold puts the oil change interval into the severe service category, which is 3000 miles for most vehicles. Synthetics can be run two to three times the mileage of petroleum oils with no problems. They do not react to combustion and combustion by-products to the extent that the dead dinosaur juice does. The longer drain intervals possible help take the bite out of the higher cost of the synthetics. If your car or bike is still under warranty you will have to stick to the recommended drain intervals. These are set for petroleum oils and the manufacturers make no official allowance for the use of synthetics.

Oil additives should not be used. The oil companies have gone to great lengths to develop an additive package that meets the vehicle's requirements. Some of these additives are synergistic, that is the effect of two additives together is greater than the effect of each acting separately. If you add anything to the oil you may upset this balance and prevent the oil from performing to specification.

The numbers above are not, by any means, all there is to determining what makes a top quality oil. The exact base stock used, the type, quality, and quantity of additives used are very important. The given data combined with the manufacturer's claims, your personal experience, and the reputation of the oil among others who use it should help you make an informed choice.

Addendum

I just received this data from our local oil distributor. It is the update on the new Mobil 1 formulation and that for the new Castrol Syntec. They did not have the numbers for the new Valvoline synthetics yet. The data on the new Mobil 1 is pretty impressive. Based on these numbers, price, and availability, there is little need to look further for a synthetic oil.

The Syntec seems to be compromised by it's wide viscosity range. Notice that the pour point is for all practical purposes, no better than the Mobil 1 15W-50 (actually, it's not as good). While, meeting the viscosity parameters, the wide range is probably for marketing purposes. The Mobil 1 15W-50 will pump at -35 degrees F, which is as good as some conventional 5W-30 oils.

Any of the ester based synthetics (AMSOIL, Mobil 1, and Syntec), will give you the benefits that Castrol is making a big deal of in their advertising. The ability to cling to metal walls is due to the polar nature of the ester base stock, not something unique to Castrol's formulation.

Motor Oil Data

 

Listed alphabetically, data not available indicated by ---



Brand            V.I.    Flash   Pour    %ash   %zinc

------------------------------------------------------------

Syntec 5W-50     180     437     -49     1.2    0.10

Mobil 1 5W-30    165     445     -65     ---    ---

Mobil 1 10W-30   160     450     -65     ---    ---

Mobil 1 15W-50   170     470     -55     ---    ---

------------------------------------------------------------

John,
The difference between 20w/50 and 50 is the 20w/50 is a multi-viscosity and single viscosity. They both have their uses. Multi-viscosity is usually a high quality 25 to 35 weight oil with a elastic synthetic polymer to react to changing temperatures to stabilize the oil through the temperature ranges of a 20 to a 50 weight motor oil. Simply, it protects your engine at cold start ups and high temperature demands without breaking down.

A 50 weight oil can be used in just high stress and high temperature demands. Mostly racing and aviation conditions. It requires warm start up temps and extended engine warm ups. The theory is, a straight weight oil will not break down in stressful situations as a multi-viscosity might do. This was true years ago but with modern oils and polymer packages this is not as likely. A couple other points, a synthetic is modified carbon molecule that has a seven vs. a natural six sided molecule, thus making it more luberious and slippery. It also can penetrate rings on older cars and loose gaskets. All oils are designed for specific purposes. All motor oils are not made for all applications.
Hope this helps.

Bill
================

At 10:18 AM 4/14/01, Don Hanson wrote:
Here is a related question.  I am sometimes forced through lack of planning to either use a different oil, or go without.  Since running with a low oil level is not an option, how bad is it to mix in a couple of quarts (sometimes that much, after an open road race run at 160mph/100miles in 90+ temps) to bring the level back to full? Many times in my travels I have been forced to use Mini-mart or Mom and Pop gas station brands to top up my fancy multi-grade synthetic.  Is this a total no no?  I make it a point to change as soon as I can after mixing brands/weights/synthetic/non-synthetic.


The cheapest, nastiest oil that you can buy is better than running out of oil.

But: I would rather run one quart low (in normal street driving) than put a non-spec oil in the engine.

The "spec" refers to the American Petroleum Institute's (API) rating system. Porsche calls for Se in the oldest 928s, SG in the newest. The current spec is SJ, which is the desired spec for any 928 - at least until SL comes out in the fall of 2001.

Flat statement here:
Any API SJ oil will give satisfactory service for street use in any 928.

Some oils are better than others. The trick is in separating the marketing from the engineering. Some people swear by synthetic, some by dino, some by Mobil-1, some by RedLine. Your money, your engine.

Just remember that engine oil is religion, not logic, and you aren't going to change anyone's mind with your testimonial.

Wally Plumley