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oilman
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Joined: 28-June-2004
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Topic: Myths and misconceptions (oil viscosity) Posted: 27-April-2005 at 10:33 |
I see it mentioned so many times on discussion forums and I feel that it would help if I cleared up a common misconception.
I often see comments like:
"Do not use 5w oils"
"5w oils are too thin"
"Use 10w-40 but not 5w-40"
Some facts need to be straightened out here and hopefully I can do this without losing those that are interested.
So what is the difference between a 5w-40 and a 10w-40 @100degC?
Basically NONE!
SAE determines the viscosity (+/-) that the oil needs to be at 100 degC and these need to be met in tests to give the oil it's API rating (xw-xx or xxw-xx).
They are as follows: (within a margin)
SAE 30 = 11.00cst SAE 40 = 14.00cst SAE 50 = 18.50cst SAE 60 = 24.00cst
Compare these SAE 40 oils at 100degC (0w, 5w, 10w, 15w)
Motul 300V 5w-40.................Viscosity = 13.80cst Motul 300V 10w-40................Viscosity = 14.00cst Silkolene PRO S 5w-40............Viscosity = 14.89cst Motul 8100 X-cess 5w-40........Viscosity = 14.00cst Fuchs Titan Supersyn 5w-40....Viscosity = 13.60cst Castrol Performance 10w-40.....Viscosity = 14.50cst Silkolene XTR 10w-40 (semi).....Viscosity = 14.70cst Mobil 1 0w-40........................Viscosity = 14.30cst Motul 8100 0w-40...................Viscosity = 13.30cst Silkolene Turbolene D 15w-40....Viscosity = 14.40cst Total Quartz 15w-40...............Viscosity = 14.50cst
These figures are not by chance and include synthetics, semi-synthetics and mineral oils they are all in the range to be labelled a Xw or XXw-40 multigrade oil.
So, what's the "W" number all about then?
It stands for "winter" not "weight" as often confused and called on many U.S. articles on oil!
This number is the "cold crank" viscosity and nothing to do with the oil viscosity when the engine is up to temperture. These numbers are related to the oils ability to operate in cold temperatures. 0w oils were originally designed to operate in arctic climates that's why they operate at ferrous monkey endangering temperatures of -35degC and below!
The benefits of the lower viscosity oils (0w and 5w) is that they flow more easily and quickly when cold and therefore protect the engine better on cold start when 80% of the engine wear occurs.
So, yes it's true an sae 40 is an sae 40 when hot whether its a 0w, 5w, 10w, 15w or whatever and that's a fact. The same goes for 20's, 30's, 50's, 60's and so on.
Hope this helps.
Cheers Simon
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Brucey
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Joined: 07-March-2004
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Posted: 27-April-2005 at 13:52 |
good point!
Any comparative information on oil degradation via the various mechanisms that degrade oil? We all know that good synthetics resist heat better, but what about;
shearing in the cam and its followers
moisture
unburnt fuel
blowby gases
etc.
are some additive packs worse than others, or are wider range multigrade oils more susceptible to certain forms of degradation?
cheers
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~~~~~~~ Brucey ~~~~~~
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oilman
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Posted: 27-April-2005 at 17:04 |
Yes I do, just give me some time to put it together.
Cheers
Simon
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pma1ums
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Joined: 12-October-2004
Location: central uk
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Posted: 28-April-2005 at 05:33 |
thank you for the infomation
as my car is up for renewable oil stuff ..it helped make my choice ...
very informative info ...
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its a dogs world out there
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micky_h
Really Senior Member II
Joined: 17-February-2003
Location: United Kingdom
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Points: 798
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Posted: 28-April-2005 at 06:35 |
Hope it helped make your choice you where to buy it from too
Got to admit I've enjoyed reading the Oil thread and this.Really interesting and helped me make my choice for Oil too.Needless to say I don't think I'll be buying anymore 'shed' grade oil no matter what car I'm running.
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andyt323i
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Joined: 05-January-2005
Location: Manchester/Sheffield
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Posted: 30-April-2005 at 18:29 |
I have seen BMW is recommending castrol SLK nowadays, is anyone using this stuff?
Edited by andyt323i
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oilman
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Posted: 01-May-2005 at 10:26 |
andyt323i wrote:
I have seen BMW is recommending castrol SLK nowadays, is anyone using this stuff? |
Do you mean the SLX?
If so, yes it is very good quality oil.
A true pao synthetic with the BMW LL01 approval.
Cheers
Simon.
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shorty
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Posted: 01-May-2005 at 12:02 |
SLX :- Just bought it from my Dealer here in Scotland £10.00 a litre so it better be good stuff !!!! Ha - Ha !!!!!!!
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oilman
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Posted: 01-May-2005 at 13:05 |
shorty wrote:
SLX :- Just bought it from my Dealer here in Scotland £10.00 a litre so it better be good stuff !!!! Ha - Ha !!!!!!! |
£10 a ltr, no need to pay that.
Next time drop me a mail, £8.20 a ltr from us.
Cheers
Simon.
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Use the code BAVBOARD and get 10% Club Discount email: sales@opieoils.co.uk Phone: 01209 202944
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