SpLiT

Oil
What do all those numbers mean on the oil?




This is just a basic introduction or a briefing on oils.

There are two measures that are used to determine the properties of oil - the service index and the viscosity.
Viscosity:
This is a measure fluids resistance to flow.
As an example we will use water. Water has a viscosity somewhere around 1 (around 1.5 for Adelaide) treacle has a viscosity close to 100. Back in the beginning oils were known as "single weight" oils - they had a single viscosiy number of somewhere between 5 and 90 SAE (Society of Automotive Engineers). So a 5 weight oil was really thin and a 90 weight oil was really thick. Typically rear axles ran on 90 weight oils and vehicles that operated in extremely cold climates used 5 weight.
It was discovered in the 50's that extreme cold weather broke down some oils so that they were ineffective and therefore modifiers were added to the oils. They then gained the "W" designation in their name. And then there were 5W, 20W etc.

One of the major problems that occur with single weight oils is that it doesn't operate effectively over the full range of operating conditions. When your engine is cold you want an oil that flows freely and rapidly so that you achieve the desired lubrication for moving parts (the same goes when operating in cold climates). Oils which thin enough to satisfactorily perform that task are ineffective for temperatures rise and therefore they would not "cling" to the friction surfaces as well as the heavier (thicker) more viscous oils. You can test this theory very simply by heating some Honey - as it heats it becomes easier to pour (it actually loses its viscosity in the heating process) and will not "cling" to the pan the way it does when cold.
This led to the development of further viscosity modifiers that altered the effectiveness of the oil as it rose in temperature. This improvement in oils allowed a lightweight oil to be used (for cold running lubrication) that gradually increased in viscosity as it increased in temperature - this was the exact reverse of the honey effect that was discussed above. And with that was born the multigrade oil - and the terminologys that we are now familiar with such as SAE 20W40.
At a closer inspection of your oil bottle will reveal the second set of standards applied to oil which is the API rating - which is also known as the Severity Index. Without going into too much detail, oils are graded under this from lowest SA through to highest (SJ) - typically oils used in this country are to be at least SF/SG. Most oil company's web sites have the classifications listed.
The major breakthrough in oil technology has been the introduction of synthetic oils - partly driven by oil shortages. Also by the fact that higher proportions of the oil in our engines is made up of chemical additives anyway.
The first check point when choosing an engine oil should be the manufacturers handbook guidelines - they have been developed after a lot of testing and represent a reasonable compromise between cost and performance. You should only use oils from a reputable manufacturer - there are significant differences in the quality of the base used and this can severely impact the protection that should be provided by the oil. Conditions of use will not only impact on the oil change intervals but will also have some bearing on the grade of oil used. Australia goes through some real extreme weaher and oils that perform best in the hotter weather will not offer the same cold climate protection. A rule of thumb ( if you would like you may confirm this with your service technician) it is acceptable to drop one oil grade (ie 20W40 to 15W40) in extremely cold weather.







thanks lil for the submission of this article

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New - VH 304 with N20 - 382rwhp without gas
SKIT58

OLD VH SL/E 308 on giggle
OVH308

355's are like belly buttons everyone has one and all they are good for is collecting dust

shoot

just dont use shell very low grade

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cheers matt

mark

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