www.gt4dc.co.uk
Maintain, Modify and DRIVE your GT-Four


It is currently Thu Mar 28, 2024 11:31 pm




Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: Engine Oil Viscosity
PostPosted: Fri Oct 11, 2013 2:51 pm 
Offline
Group N
User avatar

Joined: Tue May 02, 2006 4:16 pm
Posts: 435
Location: SW
Car Model: None
Engine Oil Viscosity

Viscosity is the most misunderstood aspect of oil and yet it is the most important.

Viscosity is the force required to shear (break) the oil at a certain speed and temperature. Oils work because they have viscosity; the drag of a rotating part pulls oil from a low-pressure area into a high pressure area and “floats” the surfaces apart. This is called “hydrodynamic lubrication” and crankbearings depend on it.

Oil must be capable of flowing at low temperatures, so that it gets around the engine in a fraction of a second at start-up and must protect engine components at high temperatures without evaporating or carbonising and maintain adequate (not excessive) oil pressure. Many people think that the thicker the oil, the better the protection, but if the oil is too thick, it will not flow properly, leading to reduced protection.

The numbers on every can of oil indicate its performance characteristics when new but there are many misconceptions on what these numbers actually mean.

For multigrade oils you will see two numbers (for monograde oils only one). The first is followed by a “w” and is commonly 0, 5, 10, 15 or 20. The second number is always higher than the first and is commonly 20, 30, 40, 50 or 60. The first and second numbers ARE NOT related.

The “w” number (0, 5, 10, 15 or 20)
When multigrade oils first appeared, a low temperature test called “w” (meaning “winter” not weight) was introduced. Using a “Cold Crank Simulator", the test measures the oils ability to flow at low temperatures. ALL oils are THICKER at low temperatures than at high temperatures but the lower the “w” number, the quicker the oil will flow at low temperatures.

The second number (20, 30, 40, 50 or 60)
This number is known as the SAE (Society of Automotive Engineers) number and is measured in “Centistokes” (cst) at 100C. 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 thicker the oil.

An oils cst at 100C determines its SAE rating within the following parameters.
SAE 20 = 5.6 to less than 9.3cst
SAE 30 = 9.3 to less than 12.5cst
SAE 40 = 12.5 to less than 16.3cst
SAE 50 = 16.3 to less than 21.9cst
SAE 60 = 21.9 to less than 26.0cst

ALL oils labelled 40 must fall within the SAE parameters at 100C so everything from a monograde 40 to multigrade 0w-40, 5w-40, 10w-40, 15w-40 or 20w-40 are approximately the same thickness at 100C.

Some oil companies label oils as SAE 35, 45 or 55, but as you can see from the above figures, there isn't a SAE 35, 45 or 55. This "could" be because they are approximately on the boundary of the two grades, but as we don't deal with any of those I can't really comment further.

Summary

Cold start.
A 5w-40 will flow better than a 10w-40.
A 10w-50 will flow better than a 15w-50
A 5w-40 is the same as a 5w-30

At operating temperatures.
A 10w-50 is thicker than a 10w-40.
A 15w-50 is thicker than a 5w-40
A 0w-40 is the same as a 10w-40

If you look above, you will see that the figures quoted do not indicate at all as to whether the oil is synthetic or mineral based... Well except for 0w oils as synthetic PAO basestock is required to acheive this viscosity.

Generally the oil you use should be based on the manufacturers recommendation found in the owners manual, but then modifications, climate and the type of use can affect that recommendation. If you are unsure of what is the correct recommendation for your car and would like to know more please contact us here oilman@opieoils.co.uk

With thanks to John Rowland of Fuchs/Silkolene

Cheers

Tim and the Opie Oils team

_________________
Use the code GT4DC and get 10% Club Discount
oilman's website: http://www.opieoils.co.uk/ - register for news and offers
email: sales@opieoils.co.uk
phone: 01209 202944 WD40

Image


Top
 Profile  
 
 Post subject: Re: Engine Oil Viscosity
PostPosted: Fri Oct 18, 2013 7:46 am 
Offline
Group N

Joined: Fri Apr 06, 2012 6:13 pm
Posts: 406
Location: Weymouth southwest dorset
Car Model: None
Good read, could possibly be 'pinned' admin for future reference.....??

_________________
1998 ford st24, 186hp 2.5 v6- sold
1997 bmw e36 318ti, mint hellrot red- sold
1992 celica gt4 st185- td04 340hp/330lbs
1998 mercedes E280- sold
1998 pug 1.9 td- mile muncher!
1993 rx7 542hp savage monster!!
2007 BMW 335i- in the shop gettin built!! :-)


Top
 Profile  
 
 Post subject: Re: Engine Oil Viscosity
PostPosted: Fri Oct 18, 2013 9:31 am 
Offline
Group N
User avatar

Joined: Tue May 02, 2006 4:16 pm
Posts: 435
Location: SW
Car Model: None
That would be appreciated

_________________
Use the code GT4DC and get 10% Club Discount
oilman's website: http://www.opieoils.co.uk/ - register for news and offers
email: sales@opieoils.co.uk
phone: 01209 202944 WD40

Image


Top
 Profile  
 
 Post subject: Re: Engine Oil Viscosity
PostPosted: Tue Nov 12, 2013 10:27 pm 
Offline
New Poster

Joined: Sat Oct 19, 2013 9:28 pm
Posts: 18
Car Model: ST185 CS/RC
I use gulf 10W60 in my st185cs! very good oil


Top
 Profile  
 
 Post subject: Re: Engine Oil Viscosity
PostPosted: Wed Nov 13, 2013 9:44 am 
Offline
Group N
User avatar

Joined: Tue May 02, 2006 4:16 pm
Posts: 435
Location: SW
Car Model: None
It is, but unless it's heavily modified and used on track, I would have thought it's far too thick. Generally a 10w-40 or 10w-50 is a better choice for a Celica.

Cheers

Tim

_________________
Use the code GT4DC and get 10% Club Discount
oilman's website: http://www.opieoils.co.uk/ - register for news and offers
email: sales@opieoils.co.uk
phone: 01209 202944 WD40

Image


Top
 Profile  
 
 Post subject: Re: Engine Oil Viscosity
PostPosted: Thu Nov 14, 2013 6:06 pm 
Offline
Group B
User avatar

Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3679
Location: Bournemouth
Car Model: None
I'm guessing Spanish temperatures may justify the thicker grade oil.

_________________
If at first you don't suck seed, try drier grain.

Image


Top
 Profile  
 
 Post subject: Re: Engine Oil Viscosity
PostPosted: Thu Nov 14, 2013 6:20 pm 
Offline
Group N
User avatar

Joined: Tue May 02, 2006 4:16 pm
Posts: 435
Location: SW
Car Model: None
In Spain, a thicker grade could make sense, depending on the use it gets, oil consumption and oil temps.

Cheers

Tim

_________________
Use the code GT4DC and get 10% Club Discount
oilman's website: http://www.opieoils.co.uk/ - register for news and offers
email: sales@opieoils.co.uk
phone: 01209 202944 WD40

Image


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 


Who is online

Users browsing this forum: No registered users and 24 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group