Oil questions

**MarkH** · 19th July 2015, 20:28

Originally Posted by Flip

Compared to a mono grade oil they are thinner cold and thicker when hot.

Yeah, sorta, but you get that they are not actually thinner cold and thicker hot, don't you?
They are thinner as they get hotter and thicker the colder they are, just not as much as older types of oil like 30w40.

I do wonder what mono grade oil is exactly. An oil without a w rating would still be more viscous when colder and less viscous when hotter.

**MarkH** · 19th July 2015, 20:35

Originally Posted by Flip

As a rule of thumb 0W30 oils for really cold enviroments and 20W60 for the desert. The 15W40's are all fine for NZ.

This is also something to be careful of.
In cold environments and in the desert the fully warmed operating temperature of the engine is the same (controlled by thermostat). So using a 30 weight oil or a 60 weight oil in the same engine would be a bad idea. In colder climates using a 5w40 oil may be better than using a 15w40 oil due to the lower pour point, but either is a 40 weight oil at operating temperature. 20w60 oil should only be used for engines designed to run with 60 weight oil. 0w30 oil should only be used for engines designed to run with 30 weight oil.

**Kickaha** · 19th July 2015, 20:53

Originally Posted by MarkH

20w60 oil should only be used for engines designed to run with 60 weight oil. 0w30 oil should only be used for engines designed to run with 30 weight oil.

I bought some Penrite Mineral HPR 20W60 today, it will be used in an engine which originally specified 30W and now most people run 20W50 in them

On the Oil container it says " may be used where a 20W50 or 30W oil is recommended"

**pritch** · 19th July 2015, 21:00

Originally Posted by Katman

I thought oil intended for wet clutch use should contain no friction modifiers.

Me too.

My advice to the OP would be to try and find out what oil the manufacturer recommends and use that. RTFM?

Internet oil threads can become quite ummm exciting?

**Flip** · 19th July 2015, 21:28

Originally Posted by MarkH

Yeah, sorta, but you get that they are not actually thinner cold and thicker hot, don't you?
They are thinner as they get hotter and thicker the colder they are, just not as much as older types of oil like 30w40.

I do wonder what mono grade oil is exactly. An oil without a w rating would still be more viscous when colder and less viscous when hotter.

A mono grade oil is a old school oil with out any Viscosity Index additives (V.I.). Pre 60's oil technology.

Multigrade grade oils are thinner when cold and thicker when hot. Thats what multi grade oils are. Thats what the V.I. additive does. A say 20W40 oil is the same viscosity cold as a 20 weight oil and the same viscosity as a 40 weight oil hot. Its as simple as that.

One interesting thing is a 20w40 oil is blended from 20 weight base stock. The V.I. additive is like gorilla snot (it actually looks like a head cold) the additive is not very shear stable and breaks down with shear/work (espcially gear boxes). Thats why oils thin with use. Thats also why your bike always changes nicer with new oil. Thats also why bikes change their oil sooner than cars, they are harder on oils. Synethic oils have less VI addatives (some none) so provide better more stable life espcially in bikes.

**Old Steve** · 19th July 2015, 21:33

Actually the SAE W grade and the straight grade are not two points on a viscosity curve. They are two totally different measurements. The W grade is a measurement of dynamic viscosity, that is the viscosity of the oil while it is not moving, at a low temperature so it reflects the oil's performance at start up and how the viscosity of the cold oil affects cold cranking - the W grade is measured in centipoise at different temperatures, the SAE 15W is measured at -15 deg C (I can always remember that one), SAE 10W is measured at -20 deg C, SAE 5W at -25 deg C etc. There is also a cold cranking test where the oil has to have a cold cranking viscosity less than a stipulated target at a much lower temperature for each W grade. The straight SAE grade measures kinematic viscosity, the viscosity of the oil when moving, measured in centiStokes. Each grade has a range of viscosities which the oil must be between to meet that grade, viscosity is measured at 100 deg C for all grades. The straight grade must also meet certain shear stability targets set at a higher temperature and under shear conditions to simulate the oil's shear stability in the ring belt area.

Wet clutch motorcycle engine oil does contain friction modifiers, they allow us to slip our clutches (along with the cooling effect of the clutch being surrounded by oil and the lubricity effect of the oil as well) and there are specific tests that the oil must meet to be classified JASO friction modified (used to be JASO MA, but I think there are later classifications now).

Zinc is an anti-wear additive, it also has anti-oxidant properties. It comes in the form of primary or secondary, zinc di alkyl (or di aryl) thiophosphate, it's a sulphur phosphorus compound. Zinc has no detergent properties. Detergents are organic bases which are also used to neutralise acid by-products of combustion or oxidation. Zinc does have a slight effect on catalysts, so latest PCMOs (passenger car motor oils) are starting to use non-zinc organic anti-wear additives similar to those used in locomotive engine oils for a long time.

Detergents are mainly based on calcium or magnesium organic compounds and their function is to remove contamination particles from engine surfaces. An engine oil will also contain organic dispersants which surround contaminant particles and hold them in suspension in the oil, these dispersant additives also provide a slight detergent function in that they will strip contaminant particles from the engine wall to a certain extent, but not to the extent that the detergent will.

And multigrade engine oils don't get thinner at low temperatures and thicker at higher temperatures, no oil can. What they do is that they thicken less as temperature drops, and thin out less as temperatures rise. For most motor vehicles in New Zealand, an SAE 15W-40 is usually a good viscosity grade choice. But certain vehicles have specific viscosity requirements for our ambient temperature ranges which are specified by the manufacturer.

Then there's the performance classification of the oil, but we won't go into that here.

**MarkH** · 20th July 2015, 14:58

Originally Posted by Flip

Multigrade grade oils are thinner when cold and thicker when hot. Thats what multi grade oils are. Thats what the V.I. additive does. A say 20W40 oil is the same viscosity cold as a 20 weight oil and the same viscosity as a 40 weight oil hot. Its as simple as that.

And yet on the technical information from Mobil the viscosity at 40° is thicker than at 100°.
Some of the stuff you posted is more or less correct, then other stuff like quoted here - not so much.

Just think about 0w30, if it was the same viscosity cold as 0 weight oil then it would not be able to protect an engine, logically this just can't be the case.
It seems that Old Steve has a better understanding of oils, I certainly don't know enough to pull him up on anything he has said.