10w-60 My reasoning, an explanation

[Opie Oils]

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

[Kieran]

Very interesting information.

Been thinking about Amsoil's ultra-ninja super 0w30 brew, seeing as the car will occasionally be put on track, and also because it's getting cold...... Is this on the flip side and too thin?

[Wodjno]

Interesting read and information that is well needed ! So on reading this thread my first thought is, get myself an oil temp gauge and watch how my driving style affects the oil temperature over a week or so.. Then from this information i should be able to form the correct choice in oil..
Before this is put into practice my idea is that somewhere arond the 10/40 to 10/50 mark is going to be about right. Or maybe even 5/40 to 5/50

[Opie Oils]

Very interesting information.

Been thinking about Amsoil's ultra-ninja super 0w30 brew, seeing as the car will occasionally be put on track, and also because it's getting cold...... Is this on the flip side and too thin?

I think you'll find a decent 5w-40 synthetic is closer to the mark for a daily driver.

Cheers
Simon

[Opie Oils]

Interesting read and information that is well needed ! So on reading this thread my first thought is, get myself an oil temp gauge and watch how my driving style affects the oil temperature over a week or so.. Then from this information i should be able to form the correct choice in oil..
Before this is put into practice my idea is that somewhere arond the 10/40 to 10/50 mark is going to be about right. Or maybe even 5/40 to 5/50

Make sure the oil temps are measured in the sump. I would say that unless it's modded/used on track, 5w-40 will be the correct choice.

Cheers
Simon

[Kieran]

I think you'll find a decent 5w-40 synthetic is closer to the mark for a daily driver.

Cheers
Simon

Okay, but why? I would've thought a 0w would provide better cold-start protection?

[Opie Oils]

It does, its the SAE30 thats not ideal, that is really a longlife/fuel economy grade.

You could go 0w-40 if you wish.

Cheers

Simon

[Opie Oils]

It does but you need to look at the temps it's rated at.

Visc.........Crank/Max/Temp.....Pumping/Max/Temp

0W..............6200 at -35.............60 000 at -40
5W..............6600 at -30.............60 000 at -35
10W............7000 at -25.............60 000 at -30
15W............7000 at -20.............60 000 at -25
20W............9500 at -15.............60 000 at -20
25W............13 000 at -10..........60 000 at -15

It'll be a cold winter, for sure but....not that cold!

Cheers
Simon

[Wodjno]

It does, its the SAE30 thats not ideal, that is really a longlife/fuel economy grade.

You could go 0w-40 if you wish.

Cheers

Simon

I take it that the first oil value ( 0w ) is affected by heat aswell.. So in the summer would the oil be to thin whilst the engine is warmed up or does this not matter ?

[Opie Oils]

The viscosity increases as it gets colder so it's thicker at -30degC than it is at 0degC and at 0degC its around 40 times thicker than it is at 100degC.

Cheers
Simon

[bernmc]

Been thinking about Amsoil's ultra-ninja super 0w30 brew,

I've got this stuff in at the moment, and a lab analysis kit waiting for a sample. Once I hit 4500 miles, I'll be sending some off to the lab for a full check.

Boys at Xtreme also thought it might be a bit thin, but what do those stupid plonkers know... inhibitor switch my 4rse !!! Stick it in, I said!

Edit - just to point out - I'm very happy with the stuff so far. My commute is 80 miles/day town + M6, and the oil is still cleaner than my car

[amsoil]

We wish to point out that 5w-30 is the manufacturers recomended product for most of these cars (please check) and is therefore what we recomend; Our ASL would do the job very nicely and for track use our highest spec TSO, (a 0w-30 but with a film strength higher than many 40 weight oils)

[Opie Oils]

Indeed, OATS (a proprietory database that we use) recommends 5w/10w-30.

Another, Olyslager (once again proprietory) recommends 5w/10w-30 or 5w/10w-40.

Depending on state of tune and use you may be outside the envelope of OEM recommendations so be sure to ask first if you have a "special car".

I personally have no qualms with 0w-30 but there are many experts in the car trade who would caution the use of 0w-30 but not always for the right reasons.

Cheers
Simon

PS. You might also want to check out Castrols recommendation here (0w-30/10w-40) they use OATS as well.

http://www.castrol.com/castrol/castr...ategoryId=3205