Oil Specification & viscosity Info. - Webmaster
At the request of one of the forum members in the thread National Oil Change?, the following information on oil specification has been provided by "oilman"


Oil Specification

Most oils have both petrol and diesel ratings which are labelled by their API or ACEA ratings. The ratings are as follows but at those prices, you'll be getting what you pay for.

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


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


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.

ACEA Specifications
(Association des Constructeurs Europeens d?Automobiles)

ACEA ratings are prefixed with ?A? for petrol, ?B? for light or passenger car diesel and ?E? for heavy duty diesel.

The current specifications are:

A1 Fuel economy petrol
A2 Standard performance level
A3 High performance and/or extended drain
A4 Reserved for future use in certain direct injection engines
A5 Combines A1 fuel economy with A3 performance

B1 Fuel economy diesel
B2 Standard performance level
B3 High performance and/or extended drain
B4 For direct injection car diesel engines
B5 Combines B1 fuel economy with B3/B4 performance

E1 Non-turbocharged light duty diesel engines
E2 Standard performance level
E3 High performance and extended drain
E4 Higher performance and longer extended drain
E5 High performance and long drain plus API performances

Oil Viscosity - Webmaster
More Excellent information from Oilman. Taken from the thread Oil Viscosity


Oil Viscosity

It's thicker when cold 10w instead of 5w (poorer cold start protection) and thicker when hot sae 40 instead of 30 (will withstand higher operating temps).

This may be of help:

What is this thing called viscosity?

It?s written on every can of oil and it?s the most important visible characteristic of an oil.
The viscosity of an oil tells you how it reacts in certain circumstances and how it performs as a lubricant.
When a oil is subjected to external forces, it resists flow due to internal molecular friction and viscosity is the measure of that internal friction. Viscosity is also commonly referred to as the measurement of the oils resistance to flow.

There are two methods of viewing an oils resistance to flow. Firstly there is Kinematic Viscosity which is expressed as units indicating the flow of volume over a period of time and this is measured in centistokes (cSt).
An oils viscosity can also be viewed by measured resistance. This is known as Apparent Viscosity and it is measured in centipoises (cP).

However in the real world an oils viscosity is also referred to in such terms as thin, light and low etc. This suggests that the oil flows or circulates more easily. Conversly, terms such as heavy and high etc suggest the fluid has a stronger resistance to flow.

The reason for viscosity being so important is because it is directly related to the oils load-carrying ability - The greater an oils viscosity, the greater the loads that it can withstand. (It must be added when new not over a period of time as all oils ?shear down? with use)

An oil must be capable of separating the moving parts in your engine at the operating temperature. On the basis that an oils viscosity is related to its load carrying ability, you could be fooled into thinking that ?thicker? oils are better at lubricating but, you?d be wrong in this assumption. The fact is that in the wrong application a high viscosity oil can be just as damaging as using a low viscosity oil.

The use of an oil that?s too ?thin? can cause metal-to-metal contact, poor sealing and
increased oil consumption and conversely, an oil that?s too ?thick? can cause increased
friction, reduced energy efficiency, higher operating temperatures, and poor cold starts in cold temperatures.

It is very important that you select the correct oil, not too ?light? or too ?heavy? and your Owners Handbook is a very good place to start as it lists the temperatures and options.

Oils thicken at low temperatures and thin as the temperature increases. The actual rate of change is indicated by their viscosity index (this number normally listed on the oils technical data sheet indicates the degree of change in viscosity of an oil within a temperature range, currently 40-100 degrees centigrade)

An oil with a high viscosity index, will normally behave similarly at these two temperatures but an oil with a low viscosity index will behave quite differently. It will become very fluid, thin and pour easily at high temperatures. A higher index is better!

Multi-grade oils are designed to perform at high and low temperatures by adding polymers to a base oil (5w,10w, 15w etc) which are heat sensitive and ?uncoil? to maintain the higher viscosity sae 30,40,50 etc. This means that the oil can be used ?all year round? rather than using different oils for summer and winter.

It is important to understand that the selection of the correct oil for your car is not just guesswork, you must consider the temperatures at which you need the oil to operate a 0w, 5w oil is better for cold starts as the oil circulates more easily when it?s cold and is able to flow around the engine more easily and quickly, offering protection at the
critical moments following cold engine start-up. These oils are also known to give better fuel economy and engine performance.

Finally, all oils ?shear? or thin down with use and this means that an oil that started life as a 10w-40 will with use become a 10w-20. The period of time this takes depends on the type and quality of the oil. The most ?shear stable? oils are proper Synthetics, either PAO (Poly Alph Olefins) or Esters which have very high thermal stability. They are in general of the more expensive variety but last longer and give the best levels of protection.



Also see Simon's latest contribution on the subject of oil HERE

And some more stuff:-
Gear Oil Questions and Answers
16 important OIL questions answered
What does 10w-40 mean..?

Edited by Dynamic Dave on 22/02/2008 at 13:40


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