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

 

 

I appreciated that Oilman,

thanks

Edwin

 

The reality, which you simply don't seem to grasp simon, is that while a good oil is okay for prolonged periods at 130ºC, a subaru isn't and will do a bearing. I agree in this weather oil requirements are a little different, and we service standardish cars with 10w40, but there is a place in subarus for thicker oils.

 

I use a sythetic 15/50 all year long I presume this is ok?

 

I totally appreciate it and that's exactly the point.

Most scoobs don't run these temperatures for that very reason and the lower the oil temps the more dangerous it is to run a thick oil.

It is a complete myth that you should use a thick oil if oil temps are within the 70-100degC range as the oil remains to heavy.

Cheers
Simon

Yes 15w-50 is fine for modded and track cars where required.

 

Okay,

so i have a standard 02 sti, what oil should i be running? it will be taken to approx 330bhp in the new year, will i have to change grades of oil?

Car is general fast road and possible light track use.

advise please

 

You should be using a quality 5w-40 synthetic. You will only need to step up to an sae 50 synthetic if oil temps are excessive (above 120degC).


Cheers
Simon

 

We are in Summer now in South Africa. Temps can go up to over 40 degrees celcius.
We are also at 1600meters above sea level. Should I be using 10w60??
I am currently using 10w40.

Edwin

 

"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."

M3?

What about localised high temperatures on bearing surfaces that are not reflected in the overall oil temperature, especially after shutdown in a turbo that after a few seconds starts to boil the coolant?

 

What about your oil temps? What do they read?

Cheers
Simon

 

Certain BMW engines use 10w-60 and it is specified, 5 specific ones if I recall correctly, I have the list.

Oil temps are measured in the sump and it's this temp that is used in calculating the figures. They can also stand higher temps in turbo centre bearings. Even in run of the mill engines, oils experience very high localised temps with no problems, just in normal road use. Oil in little end bearings reaches around 200C, and around top piston rings, 280C. Even average oils non synthetic oils are able to put up with this for 1000's miles.

Cheers
Simon

 

The BMW engines that use 10w-60 tend to be the ones where there was a big end bearing problem. Subarus suffer with their big ends as well. What is the connection?

 

There isn't John.

Alex

 

One is a high revving long stroke motor that had many recalls before the problem was fixed, and the oil viscosity specified went up from the earlier models.

The other is also well known for doing big ends with rather small bearings, and most modifiers go fairly high on the oil viscosity.

I wondered because both problems seem to be poorly understood, yet the recommendation for an increase in viscosity (either officially or unofficially) seemed to be related? Should engines with stressed big end bearings have higher viscosity oil to help protect them at high loads/temperatures?

 

So should i stop using shell 10W60? I'm using 10W60 since 20.000 kms and before that I always used what the handbook says (SemiSyn10W40(mobil 1 S)) Now, you re suggesting not to use this viscosity. Ferrari suggests this oil for most of their cars but I've never seen a Ferrari owner whois always driving fast. They are generally going slow so the oil temp is always remains cold? We re also not rallying in the streets so it is totally wasting the money from your sight of view. Choosing the right oil becomes a dilemma!

 

What year is the car? Is it modded? Are oil temps ever in excess of 120degC?

Cheers
Simon

 

It is a MY98 with some small modifications..(exthaust, ecu etc..) I've only oil pressure gauge and the car have never seen a track. daily driver =)

 

Pre 2000 cars tend to be happier on sae 50. We recommend 10w-50 or 15w-50.

10w-50 is better all year round.

Cheers
Simon

 

I've been using Castrol RS 10/60 exclusively for over 120'000kms now with no problems. Car has run between 270 and 380 hp during this time. I also run this oil in winter here in CH.

Loss of performance as a result is outweighed by better bearing protection IMHO.

Richard

 

15w 50 motul for me, even smells like bananas when fresh

 

same here but never noticed the smell..

 

Hi Simon

Dont know, dont have a gauge in there at the moment. Car is a MY98, lightly modded with a zorst, filter and chip. Do a lot of short distance driving but will be doing more long distance next year.

cheers

Edwin

 

I would probably go for a good 5w-40 for all year round use.

Cheers

Simon.

 

sorry, but this looks to me like another example of simon, answering a question that no one else asked, probably because business is slow.

Why don't you just place an ad, rather than pretend to be really conerned?

Call me a cynic, but I bet you have posted the same thread on several other forums this week, probably because business is slow approaching christmas.

Nothing wrong with making money from the net, you are after all a paid up authorised advertiser, but if you want to advertise, can you just make it clear it is an advert rater than pretend to be solving one of the great mysteries of the world and enlightening the weak minded.

 

There is an ad for a December offer.

This is a question I get asked a lot. I get over 300 emails a day off the Forums so I'm certainly not short of work, I can assure you

When I have time and that's not very often I try to compose an informative and technically correct reply to post on Forums that would be interested.

The reason this is not an advert is it's a technical post!

Cheers
Simon

 

Hi oilman, ive been reading your posts and ive not come across which type of oil i should use for my 94 wrx (260ps model) ..so its quite powerfull standard. It will be staying like this for a while.. with the only near future exception being a decent exhaust with only one cat going. what oil do you think i should be using, an all year round one would be great!.. thanks matey.

Bob

Edit: forgot to mention which brand would be good

 

informative!!! i use 15/50 mobil 1 oil. car at 300bhp. So is this oil ok then all year round??

 

I would suggest that the best all year round oil would be 10w-50 Silkolene PRO or 15w-50 Motul 300V.

The 10w-50 will be better for winter.

Cheers
Simon

 

What year is the car?

Cheers
Simon