Thread: Oil viscosity

Originally Posted by Panda

Okay, sorry about this, but I've got another stupid question for everyone's expertise.

Went to buy oil for my Series III, but couldn't remember what we usually get (or should I say, what Tony usually gets).

We always buy Penrite however, I was stunned by the different grades. They ran from 5-60, 10, 15, 30 & I think 45? (Can't remember exactly all the grades they sold).

Anyway, decided on the middle ground & bought the 15W-60. Does it make such a difference? & should you use different oils for different weather, e.g. summer v winter?? What's the optimum for an engine as old as the III?

Thanks in advance

15W is the index of thickness (simply put) the W is for Winter which means when cold the oil has a thickness (or viscosity) of 15, the closer the number to Zero (0), the thinner the oil so the other half is 60 which means when it (the oil) is Hot it's thickness is 60 or in simple terms much thicker than 15W. Most oils nowadays are Mltigrade like the oil you bought, this same oil is thin (15) when cold and thick when hot (60). That way when you start your cold engine the oil is thin enough to be pumped quickly around to all parts of the engine to lube all the moving bits, as the engine and oil gets hotter the oil gets "Thicker" (60) to properly lube all the bits that are now moving faster and have more strain and stress on them. For instance my Ford GT 5.4L V8 Quad cam engine used 0W-40 synthetic oil, because each head carried 2 camshafts and 4 valves/cylinder it needs oil to be very quickly delivered to the top of the engine to lube all of those extra parts, it is critical in Hi-Tech modern engines to get oil to these parts as quickly as possible, otherwise excess wear will occurr, unlike your SIII engine with old tech OHV's it is not critical to get the oil up to the top as quickly. I'm sorry if I have simplified this explanation too much, it's no reflection on your mechanical knowledge, but a lot of people will find it easier to understand, explained this way, Regards Frank.

Dear Frank,

Thank you so much for that reply. It was perfectly put & I now understand. Not too technical is good for me, as I'm on "L" plates as far as all this is concerned, & your response made it very easy to understand.

Much appreciated.

I do wish you'd wait till I get home I'll be back soon you know....

Have a look at this web sight its what penrite rec u\you should use.

Hodgo



http://www.penritedata.com/au/db/veh...178&x=118&y=12

Originally Posted by Tank

<snip>
That way when you start your cold engine the oil is thin enough to be pumped quickly around to all parts of the engine to lube all the moving bits, as the engine and oil gets hotter the oil gets "Thicker" (60) to properly lube all the bits that are now moving faster and have more strain and stress on them. <snip>

Sorry Frank, but that is just plain wrong.
No lubricating oil gets 'thicker' the hotter it gets. They all get thinner as temperature increases.

With the SAE viscosity range, the xW part refers to an oils pumpability at sub zero temperatures. This is actually measured as a pressure reading in centipascals (cP)
The 5W, 10w, etc refers to a specific range of pressures/temps the oil must meet at low temps.

As an oil gets hotter and thins out, its viscosity is measured at 100*C. These viscosity measurements are measured in a scale known as centiStokes. (cSt) Whatever viscosity our oil 'measures' at this temp determines which SAE viscosity range it falls into (20, 30, 40, 50, 60)

Remember that SAE xW-X numbers are not absolute, but a range that an oil falls into, and ALL of the final ranges are a lot, lot thinner than any of the W ranges.

The rate at which an oil thins is measured as its Viscosity Index (VI)
The higher the number, the slower an oil thins as it gets hotter.
Generally, the higher the VI the better, as it can be an indicator of better base oils (eg Synthetics usually have a much higher VI than a mineral based oil) but trickery can often be involved here as a blender will also use a range of polymers known as Viscosity Index Improvers that can artificially reduce the rate of thinning. These VII's are generally used with thinner type base oils to get a reasonable low temp pumpability, while still meeting the higher SAE high temp range scales. It's how a multigrade mineral oil is made.
Unfortunately VII's they have a tendency to shear in service (and more so in gearboxes, etc) and so over the life of the oil the high temperature viscosity becomes thinner and thinner.

Check out this Valvoline Synpower 5W-40 in TD5 for the relevant charts and some typical well meaning but misguided comments and answers.

Yes darling one, but you're not here now are you?

Originally Posted by tony

I do wish you'd wait till I get home I'll be back soon you know....

That's brilliant. Next time I'll get the 40. I had no idea gear oil comes in different levels as well.

Geez I'm glad I'm not a mechanic! Too damn complicated for me!

Originally Posted by hodgo

Have a look at this web sight its what penrite rec u\you should use.

Hodgo



http://www.penritedata.com/au/db/veh...178&x=118&y=12

Bloody hell! Now I'm definitely confused!

Originally Posted by rick130

Sorry Frank, but that is just plain wrong.
No lubricating oil gets 'thicker' the hotter it gets. They all get thinner as temperature increases.

With the SAE viscosity range, the xW part refers to an oils pumpability at sub zero temperatures. This is actually measured as a pressure reading in centipascals (cP)
The 5W, 10w, etc refers to a specific range of pressures/temps the oil must meet at low temps.

As an oil gets hotter and thins out, its viscosity is measured at 100*C. These viscosity measurements are measured in a scale known as centiStokes. (cSt) Whatever viscosity our oil 'measures' at this temp determines which SAE viscosity range it falls into (20, 30, 40, 50, 60)

Remember that SAE xW-X numbers are not absolute, but a range that an oil falls into, and ALL of the final ranges are a lot, lot thinner than any of the W ranges.

The rate at which an oil thins is measured as its Viscosity Index (VI)
The higher the number, the slower an oil thins as it gets hotter.
Generally, the higher the VI the better, as it can be an indicator of better base oils (eg Synthetics usually have a much higher VI than a mineral based oil) but trickery can often be involved here as a blender will also use a range of polymers known as Viscosity Index Improvers that can artificially reduce the rate of thinning. These VII's are generally used with thinner type base oils to get a reasonable low temp pumpability, while still meeting the higher SAE high temp range scales. It's how a multigrade mineral oil is made.
Unfortunately VII's they have a tendency to shear in service (and more so in gearboxes, etc) and so over the life of the oil the high temperature viscosity becomes thinner and thinner.

Check out this Valvoline Synpower 5W-40 in TD5 for the relevant charts and some typical well meaning but misguided comments and answers.