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
Simon

 

 

Great explanation.

What about the lower fuel consumption? Typo?

 

Indeed lower MPG is what I mean.

Cheers
Simon

 

Really made me think why im using a 60 oil. Seems like a 50 is a better option.

 

 

unfortunatley i havent got time to read all of it, so what oil do you recomend for a stg 3 saph thats done over 100k ?

cheers............matt

 

He's probably going to recommend 10w50 in the summer and 5w40 in the winter, I'll put a tenner on it

 

WOW i understood that

still got mates who insist on using castrol RS though

 

Indeed but 10w-50 can be used all year round.

Cheers
Simon

 

so ive got a saph that is about 450bhp which the engine has only done 2000 miles so what oil would u recommend to use 10w 50??

If so who makes the oil in that grade?

Ive always used 10w 60 castrol rs...

 

Yes mate 10w-50 is ideal.

Look at the Silkolene Pro S 10w-50 ester/pao synthetic, this is top quality and much more suited then a 10w-60 as that is a little too thick when hot.

Cheers

Simon.

 

I have PROPER oil in stock when you get here Buchimus

Silkolene Pro S 10w50 as it happens.

 

[quote="Stu @ M Developments"]I have PROPER oil in stock when you get here Buchimus

Silkolene Pro S 10w50 as it happens. [/q

your the man

 

That's what they say

The "oilman"

Cheers
Simon

 

oilman

a couple of questions

Working temp for oils in an engine, would that be between 80 and 100 degrees?

also

am i right in thinking, a SAE 60 oil is 70% thicker than a SAE 40 oil
at a temp of 100 degrees

So making a SAE50 oil Approximatly 35% thicker than a 40 at 100 degrees??

Surely in Real terms, you would see huge difference between them?
as in to actually look at your oil pressure gauge when up to temp
you would notice a big difference between them??

thanks!

 

Hi,

Yes, between 80-100 degc is optimum... a lot of people now are over cooling with their oil coolers and not going above 50-60deg.... this can be as bad as over heating the oil depending on what grade you are using.

You are quite correct about the viscosity at 100deg. However when it comes to watching the pressure guage you also have to take into account the faster flow rate of the thinner oil... the idea being the faster the oil circulates the quikcer it can cool but will read as quite low oil pressure as the pressure is a measure of resistance and not flow.

Cheers

Simon.

 

Fuckin hell, how much technology is there behind those numbers on that £40 4l bottle of oil?
Top post and im glad i read it!

 

The old ones are always the best ones.

If it saves one person from wrecking their engine due to using the wrong oil then I'm happy

Cheers
Simon

 

Best be getting rid of my castrol rs 10w-60 then
For ??? ..... 10w-50?

 

10w-50

 

I was recomended 10w60 by a local engineering/car tuning firm for my cossie, on trusting there judement and filling the engine with this I started the car on a cold morning and heard what I can only describe as a loud thudding from the bottom end, the big ends ?

OIL WAS REMOVED IMEDIATELY, (now using mobil 1 10w50) and research carried out and came up with same answer as oilman

 

iv always wondered whats best, theres alot of mixed thoughts on it where it be 50 or 60.

im just about to give the cossie a major service before silverstone... so 10w-50 is the way forward?

 

a very very interesting read

 

what about using a good branded tri-ester 10w40 for a well tuned zetec turbo?
i think a 10w50 seems a little too thick, discuss

 

Top post, but I'm sticking to my 10w-60, due to the track use and the bonkers ambient temp here!!

 

10w60 is also potentially useful if you are at risk of fuel dilution, endurance racing for example.

 

10w60 when cold is not significantly different to 10w50 surely due to the 10w in both ? so I can't see why it would make a difference in your scenario.

 

Most 10W-60 oils are crap. Don't get the hype about it.
The additive package is bad (the oil ages fast) and after some miles of hard drive it is like a 10W-35 dishwater. Maybe castrol has some good xxW-40-oils but the 10W-60 isn't up2date.

Prefer a good 5W-50 which is after 6000 miles like a 5W-48 instead of a 10W-60 which is after 3000 miles like a 10W-35 cause of the bad additives in it. The grade says nothing about the quality of an oil.

Even the manual of the cosworth recommend a 5W-50. Most I do not agree with the manual but some recommends aren't so bad. Mobil 1 is a great oil for example and has some of the best additive packages.

And ester oils are treaten with caution. To much shear stability (HTHS) do harm to the engine (to much drag for the bearings etc.). Ester oils are for motorcycles or high revving engines. Most cars do not revving higher than 9000 therefore it is needles or even bad for the engine....... a good 5W-50 has enough shear stability.

 

Oilman, do the oil specs change between a Cosworth 200 and 205 block? Would a different oil make any difference as the 205 block is not as strong?

Would a 15-50 fully synth (if they do such a thing) be OK in a 205 block running a good stage 3 power? recently been rebuilt with no piston slap etc

 

My car is Sierra Cosworth 4wd -91 ~300 hp and has 100k miles on the clock on stock internals. 10W-50 Silkolene would be the best for me? What other 10W-50 oils are good as the Silkolene has little to none availability back here?

I live in Finland and summertime temperature is beetween +5 to +30 celsius. Car might get limited winter usage when temperatures are 0 to -30 celsius. What kind of oils make the engine noisy when its cold? The ones with smaller 'W' number?

 

Interesting, ive been using 10w60 in my track MK5 RS2000 for about a year without a cooler.... guess i better move to 10w50! Do Gulf comp do this grade?

 

How come Aston Martin use Castrol 10/60 Edge inthe V8 Vantage

 

What to use on my 200 bhp S2 Rs turbo doesn't get abused btw.