Oil - The basics

[oilman]

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

[Dippy]

Very informative post - so I have sticky'd it.

There are two key issues which relate to our cars:

Oil bearing turbochargers: When starting the engine cold, if the oil is too thick (low viscosity) the bearing may not stable. Therefore aggressive use of the throttle can actually risk wear damage to the turbine. Depending on how cold the climate is, serious consideration should be given to the cold rating of the oil used (the lower the better). This adds to the "a thinner oil will circulate faster on cold start" statement above.

Camshaft wear: There have been reports that the B5 S4 can suffer premature cam wear if the oil is too thin. One German tuner recommends that the hot viscosity rating should be no less than 40.

[oilman]

I would agree with that and say that a 5w-40 is probably the most suited grade

Cheers
Simon

[harry]

Dippy, i thought the KO4's on the RS4 were water cooled with water circulating in reverse on engine shut down thus less damage/more protection to turbos. I do agree that after long time under boost the oil temp should be allowed to cool down somewhat before shut off. I was led to believe that this can happen from normal driving conditions or allowing the engine to idle for a couple of minutes.

I heard this info from a senior Audi tech tho I may have heard wrong and would appreciate being corrected.

[dummi]

k04's are water cooled but oil lubricated, from dippys post a thin oil at cold like 5w will help lubricate the bearings for mechanism of spin,, water cooling only keeps temperature under control. i was advised temperature should be allowed to cool down of oil so not to bake oil in lines around turbos if engine is switched of the oil wont circulate

[harry]

yeh that backs up what I heard too

[Dippy]

K03s and K04s are indeed water-cooled, and there is indeed an after-run pump to reverse circulate the coolant after switch-off in order to remove air bubbles (so this only happens at very high coolant temps unless the sensor is changed or the contact overriden).

But this has nothing to do with the point I made: Using the right oil to protect the turbos at START-UP.

The oil-related issue for COOL-DOWN is that a fully-synthetic oil is recommended as it is most resistant to coking.

[harry]

Thanks for clearing that up Dippy.

I was referring to cool down only as this is all I'm familiar with. My butler warms the engine suitably for me when fetching the car from my secure ambient controlled underground garage on my sprawling Highland estate.

[flashyg]

any 0w 50 available or 5w 50.
I have used the millers 10w 60.

These cars can easily get to above 100 on hard driving.
So what is the latest and best brand and spec of the moment?

[Tomson]

This is the reply I received from Guy who works with Simon yesterday...

For the RS4 you will need an oil that meets the VW503.01 spec, these are longlife oils usually 0w-30 and not really designed with performance in mind.

However the break from the norm is the Motul 8100 0w-40 which is an ester based performance oil that meets the VW503.01 spec, this would be my choice.


This is based on my High Mileage Stage III B5 RS4 and the upcoming summer trip to the south of France, High Speeds, High temperatures etc etc

Can someone quickly confirm how much I need for a full oil change? Also I was going to buy sump plug, washer and Oil Filter from VAG Parts - is everyone agreed that this is the most cost effective option.

[flashyg]

5.3- 5.5 litre.
dealer is as easy for the parts as the price is not significant.

[dace]

Surely 0W-40 is too thin? I would have thought 5W-40 a better option (Silkolene, Shell Helix Ultra or Synta Gold)..........

[flashyg]

surely you are wrong dace.
0 is simply more protection at low temps.
Would you prefer less protection?
Would you for it to take longer for the oil to get arround the engine?

There just seems to be a compromise in the perfect world a 0w 50 or 0w 60 would be fantastic.

So any other wide range highly recommended oils.

1 Motul 8100 0w-40 Tomson (who sells it, how much,what quantities)
2 ...?

[dace]

Only expressing what one of the major tuners told me! They have exsperienced problems with 0W-40...
Is it a matter of preference and opinion?

[flashyg]

What tuner? What was said?
What oil are you using?

As discussed, any thing over 0W is a compromise on cold start up.
I would have thought the discussion would have suggested higher end figures 50 / 60. Hence the request for alternate oils.