Oil recommendations and questions here - The Definitive S2 Oil thread

[s2driveruk]

interesting, can you just explain more about the 10w-60 thickness issue.....what are the dis-advantages here?
Cheers
David

[oilman]

Here is an old article we put together about this, it should explain.

I get asked all the time "why do you advise against the use of 10w-60?".

Let's get one thing clear, I supply 10w-60 and recommend it where it is appropriate for the engine or the application but conversly I caution against it's misuse!

I have debated this many times on many car forums and I know there are some that do not agree with me however I have never had a reasonable technical explanation why 10w-60 is in fact suitable, it's certainly not mentioned in the handbooks of many modern highly tuned performance cars, with the exception of some Alfa Romeos for "spirited driving" whatever that is meant supposed mean.

Explaining this is diffucult so there may be questions but I'll try my best to explain it in plain English!

Lets look at what oil specs actually mean and particularly the higher number which is in fact the oils SAE number (the "w" number is in fact the cold crank viscosity and measured in a different way) The SAE number is measured by the oils viscosity at 100degC.

Your cars require according to the manufacturers specs, sae 30, 40 and in some cases sae 50.

To attain the relevent sae number the oil has to be at 100degC (no thinner than)

SAE 30 11cst approx
SAE 40 14cst approx
SAE 50 18cst approx

Centistokes (cst) is the measure of a fluid's resistance to flow (viscosity). It is calculated in terms of the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid.

As viscosity varies with temperature, the value is meaningless unless accompanied by the temperature at which it is measured. In the case of oils, viscosity is generally reported in centistokes (cst) and usually measured at 40degC and 100degC.

SAE 60 is in fact 24cst viscosity at 100degC!

This is 33% thicker than an sae 50, 70% thicker than an sae 40 and over 100% thicker than an sae 30!

So, what's the problem with this thickness?

Well, this is measured at 100degC and at lower temps (70-90degC) all oils are thicker than at 100degC so the problem is compounded to some extent.

The downsides of such a thick oil (when not specified) are as follows:

Additional friction, heat and wear.
A reduction of BHP at the wheels
Lower fuel consumption

The thicker the oil is the more friction and drag and the more power the engine needs to move it around the engine which inevitably translates to less at the wheels.

So, when do we spec a thicker oil?

Well, you will probably have seen us on occassions recommending a 10w-50 but only in these circumstances.

1. If the car is heavily modded and heat/oil temperatures are excessive.
2. If the car is used on track and heat/oil temperatures are excessive.
3. If it's required by the handbook.

Our criteria for this is based on oil temps as an sae 40 semi-synthetic can handle around 110degC for limited periods whereas a proper synthetic sae 40 can hande 120-130degC for prolonged periods due to its thermal stability.

Once you see more than say 120degC for prolonged periods an sae 50 is adviseable as it is 18cst at 100degC and still 11cst at 130degC! This is in fact the same as an sae 30 at 100degC.

More importantly at 90degC an sae 40 is 15cst, an sae 50 is 20cst and an sae 60 is 30cst!

In a worst case scenario with thick oils (when not required) is that you will experience air entrainment and cavitation inside the bearings at high RPM. Not clever stuff!

I know this is technical stuff but oil is a combination of science and engineering and few people know enough about it to make an informed choice. Just because your mates use it and have had no problems is not a good enough reason to use it, your engine would prefer and benefit from the correct oil.

Cheers
Guy.

[s2driveruk]

great, thanks for that....i will be ordering some 15-50 then i think!

[oilman]

Or 10w-50

[Jamo]

10w50 is what you want.

Oilman what a good mineral oil to break engines in on? And thanks for the redline assembly lube

[oilman]

10w-40 semi is fine to run in with, these are 100% mineral base so fine for the job.

Cheers

Guy.

[20vQC]

So... I'll look for a 10W-50!!! What brands does Oilman recommends for this kind of oil quality???

[oilman]

http://www.opieoils.co.uk/c-659-10w-50.aspx

[A80Avant]

really in a newly rebuilt engine,would there be any problem if so far it has been used castrol 10W60 (for about 18000Kms) and then change to 10W50 oil instead?
I have read that it is bad for the the valve stem seals.Meaning that once they have been worked with the thicker oil,if you use thinner they might leak some oil and therefore have increased oil consumption...
can you verify that?
I do want to change to 10W50 as well at some point but as 10W60 was used so far,i wonder if there are going to be any concequences

cheers
vasilis

[oilman]

There will be no issue switching to 10w-50.

Cheers

Guy

[johne]

Guy,

So if you run a relatively normal ABY with it's thermostatic oil cooler which means you get oil temps. of 85 - 90 degC on average and only do normal/motorway driving would 5w (or 0w) - 30 be alright on the basis that 5 or 0w gives the best cold start protection and 30 at the other end to give lowest friction and best fuel economy? Assuming a quality synthetic and accepting the downside of higher oil consumption. Or is 0w - 40 the lowest you'd advise us to go?

[oilman]

I wouldnt really go any thinner then SAE40 really, I dont think you would have anything to gain from using an SAE30 over it.

Cheers

Guy

[A80Avant]

Changed to 10W50 a few days ago.I dont know if its the oil being new or its ingredients,but the car cranks up more easily,and reaches it's temperature faster.Also it seems to be much more lively! Used the Silkolene 10W50 Pro-S and im definitelly sticking with it.

How many Kms should i do before i change the oil again? With castrol i did around 7500Kms on everyday driving + occasional thrashing,but no track use at all.
Overall im very pleased! I just want to see the consumption(if any) on this oil.With castrol 10W60 i had around 200ml on 7500Kms.

Engine is now 30.000Kms old!

[oilman]

Silkolene Recommend 10 track hours or 9000 miles

You may consume slightly more.

It's a very good oil and deserves the accolades it gets!

Cheers
Guy

[A80Avant]

i did a little search and i may be able to get it in Greece afterall! In the mean time though! you are my provider!
cheers
Vasilis