Oil - The basics
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From: southwest
Oil - The basics
A short lesson on Multigrades:
If you see an expression such as 10W-40, the oil is a multigrade.
This simply means that the oil falls into 2 viscosity grades, in this case 10W & 40.
This is made possible by the inclusion of a polymer, a component which slows down the rate of thinning as the oil warms up and slows down the rate of thickening as the oil cools down.
It was first developed some 50 years ago to avoid the routine of using a thinner oil in winter and a thicker oil in summer.
For a 10w-40 to attain the specification target a 10W ( W = winter) the oil must have a certain maximum viscosity at low temperature. The actual viscosity and the temperature vary with the viscosity grade but in all cases the lower the number, the thinner the oil, e.g. a 5W oil is thinner than a 10W oil at temperatures encountered in UK winter conditions.
This is important because a thinner oil will circulate faster on cold start, affording better engine protection.
For a 10w-40 to attain the other specification target a 40 oil must fall within certain limits at 100 degC. In this case the temperature target does not vary with the viscosity grade, if there is no "W", the measuring temperature is always 100degC. Again the lower the number the thinner the oil, a 30 oil is thinner than a 40 oil at 100 degC., which is typical of maximum bulk oil temperatures in an operating engine.
The engine makers are, of course, very well aware of this and specify oils according to engine design features, oil pump capacities, manufacturing tolerances, ambient temperature conditions etc. It is important to follow these guidelines, they are important and are an are stipulated for good reasons.
If the engine has been modified, the operating conditions may well be outside the original design envelope. The stress on the oil caused by increased maximum revs, power output and temperature may indicate that oil of a different type and viscosity grade would be beneficial.
Cheers
Simon
If you see an expression such as 10W-40, the oil is a multigrade.
This simply means that the oil falls into 2 viscosity grades, in this case 10W & 40.
This is made possible by the inclusion of a polymer, a component which slows down the rate of thinning as the oil warms up and slows down the rate of thickening as the oil cools down.
It was first developed some 50 years ago to avoid the routine of using a thinner oil in winter and a thicker oil in summer.
For a 10w-40 to attain the specification target a 10W ( W = winter) the oil must have a certain maximum viscosity at low temperature. The actual viscosity and the temperature vary with the viscosity grade but in all cases the lower the number, the thinner the oil, e.g. a 5W oil is thinner than a 10W oil at temperatures encountered in UK winter conditions.
This is important because a thinner oil will circulate faster on cold start, affording better engine protection.
For a 10w-40 to attain the other specification target a 40 oil must fall within certain limits at 100 degC. In this case the temperature target does not vary with the viscosity grade, if there is no "W", the measuring temperature is always 100degC. Again the lower the number the thinner the oil, a 30 oil is thinner than a 40 oil at 100 degC., which is typical of maximum bulk oil temperatures in an operating engine.
The engine makers are, of course, very well aware of this and specify oils according to engine design features, oil pump capacities, manufacturing tolerances, ambient temperature conditions etc. It is important to follow these guidelines, they are important and are an are stipulated for good reasons.
If the engine has been modified, the operating conditions may well be outside the original design envelope. The stress on the oil caused by increased maximum revs, power output and temperature may indicate that oil of a different type and viscosity grade would be beneficial.
Cheers
Simon
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From: Exeter
Just to build on this, I was wondering how you modify the grade of oil to accommodate any changes in engine specification.
For example, I have always run my Cosworth on Magnatec Grade 10W40, which I think is a synthetic blend oil. The principal reason for this is that the chap who built my engine told me to!
I have on several occasions suggested to him that perhaps a fully synthetic and thinner grade oil may be more appropriate, which he has always been firmly against.
What would your thoughts be on oil grade : performance alterations? Is there any set guidance that can be followed?
Very interesting read though
JJ
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From: southwest
Yes if you mod the engine the best course to take would be to up the quality of the oil use to cope with the extra stress, temps and genaral hard use of modded engines.
If the engine is heavily modded and used hard then you combine better quality with a slightly thicker oil, usually one grade, so from a 5w-40 for a stock car to a 10w-50 to a heavily modded car.
Cheers
Simon.
If the engine is heavily modded and used hard then you combine better quality with a slightly thicker oil, usually one grade, so from a 5w-40 for a stock car to a 10w-50 to a heavily modded car.
Cheers
Simon.
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From: Cheltenham, Gloucestershire
Thats useful to know, i had some joker telling me the latter number was the maximum temperature the oil could handle 
I pretty much knew what you had said although i didnt know some of the finer aspects 
Just to clarify....the oil gets thicker as it heats up then? I had it in my head it was the other way around?
I pretty much knew what you had said although i didnt know some of the finer aspects Just to clarify....the oil gets thicker as it heats up then? I had it in my head it was the other way around?
