Oil questions

[Mustek]

Hi folks,

Is it ok to mix semi synthetic and mineral oil? They are both the same viscosity.

Do oils expire? One of them is 2-3 years old...

[pete-blen]

oil is cheap.... rebuilding a motor isn't...
Buy new oil & stop being a tight ass..

[MarkH]

Hi folks,

Is it ok to mix semi synthetic and mineral oil? They are both the same viscosity.

Do oils expire? One of them is 2-3 years old...

Oils don't expire, if exposed to air they will slowly absorb moisture though. A sealed container of oil that is 3 years old should be fine.

Yes, you can mix them, they wont explode.

Personally I wont use either of those oils though, not in my bikes.
I only use fully synthetic oil, the reasons are a bit complex - I read a ~70 page forum thread someone linked so as to be better informed on oil.
The highlights:
Fully synthetic oil maintains viscosity over a range of temperatures better than mineral oil, working better when cold and also when hot.
The important number is the 2nd one - 5w40 is bugger all different from 15w40, but 5w50 is 50 weight oil so is thicker and will cost some power/economy.
The first number (winter rating) is poorly defined, can't really trust an exact definition for it.
For motorcycles fully synthetic isn't more 'slippery' and wont make the wet clutch slip, but some additives will and therefore you need to avoid some car oils with friction reducing technology.

In my ST I'll only use fully synthetic because it only needs an oil change every 12,000kms and good oil is pretty cheap compared to >$12k for a 7 year old bike.
In my DR650 I'll only use fully synthetic because it is an air cooled bike so it experiences greater temperature variation than water cooled bikes do.
For any bike or car I've ever owned I can think of good reasons to use good oil, except maybe for one that was burning oil and would therefore get very expensive to by fully synthetic oil for.

[nzspokes]

Im using diesel oil in the Bandit. Seems to work just fine.

[MarkH]

Im using diesel oil in the Bandit. Seems to work just fine.

I'll use Mobil Delvac 1 5w40 if I can find it. It is fully synthetic oil that doesn't have the additives which bikes need to avoid, the picture of a truck on the bottle doesn't stop it from working well.

[Old Steve]

The first number (winter rating) is poorly defined, can't really trust an exact definition for it.
For motorcycles fully synthetic isn't more 'slippery' and wont make the wet clutch slip, but some additives will and therefore you need to avoid some car oils with friction reducing technology.

Quite a good summary MarkH, I'd just take exception with one comment. The first number, the W or Winter grade, is precisely defined under the SAE J300 Engine Oil viscosity specifications. The W grade addresses cold start and circulation properties, and as such the SAE specifies maximum dynamic viscosities at specific low temperatures for each W grade. There's definitely no guesswork about the specification of the SAE W grades.

And yes, a motorcycle engine oil which is also used in the transmission, should have a friction modifier for correct clutch operation. As such it should carry a JASO M classification showing it meets specific friction characteristics needed for motorbike operation. Those bikes which have separate gear box cases will use an automotive gear oil - this will have a classification under the API GL system.

And the belief that the higher the viscosity number the better the oil is not true. Internal engine clearances will determine the oil viscosity required. For instance, in my 17 year old Honda car with 150,000 km on the clock I use an SAE 5W-30, but of the highest performance classification possible. And if an oil is a synthetic (and that term is open for abuse) then that doesn't mean that it's a high performance oil. The oil additive package determines oil performance. I believe that the first Mobil 1 was not a very good oil, I think the Mobil engineers assumed that the synthetic basestock would contribute more to contamination control through it's superior oxidation resistance. They probably got it passed the performance tests required but I think that in service it wasn't such a superior oil and the additive package was upgraded not long after it's introduction. I do have, however, the highest regard for Mobil's modern synthetic oils, automotive and industrial. This from 25 years in the lubricant industry, a couple of years as the Technical Manager of one of the companies her in NZ and 9 years in that company's international technical centre.

[Kickaha]

This from 25 years in the lubricant industry, a couple of years as the Technical Manager of one of the companies her in NZ and 9 years in that company's international technical centre.

So really you wouldn't have a clue what you're talking about then

[Katman]

And yes, a motorcycle engine oil which is also used in the transmission, should have a friction modifier for correct clutch operation.

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

[Flip]

5W50 describes the viscosity at two points on the viscosity/temp curve. Basically the oil behaves like a straight SAE 5 weight oil at 0 deg C and a 50 weight oil at 100 deg C. ie, its thinner when cold and thicker when hot compared to a straight 30 weight oil. Given most wear occurs at start up and a thinner oil circulates faster the bottom number is just as important as the upper one.

All oils are mixable unless you are using Castrol R race oil as a crank case lube as its vegetable oil based. Actually there is bugger all difference between semi and mineral based lube oils.

All the light disesl oils or mixed fleet lubes are very fine motor oils. I run them myself because they are full zinc and provide better lubrication protection than "modern" motor oils. Modern motor oils are designed to extend the life of catalitic converters and are light on certan important zinc based additives.

JASO have a test for motorcycle oils compatability with wet clutches, if the oil makers market them as bike oils they will have tested their oils against this standard. There is no SAE test for clutch compatability that I know of. If I had a bike that I suspected needed a clutch comptable oil I would look for one that has been tested to the JASO clutch compatability test. In my case imMobile1 V2 does and I use it for this reason.

I run a Valvolene 10W40 diesel oil in all my other vehicles; landy, BMW, Merc, MG, Austin and Suzuki 4WD, excpt for the HD that gets inMobile 1 V2 and the Lotus that gets imMobil 1 5W50.

But then WTF do I know!

[Flip]

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

They can have some just not too much. Those pesky Zinc addatives improve the lubricitity and are also detergents, some but not too much. Gear oil molibdumin EP addatives that used to be added to some motor oils 40 years ago are wet clutch killers.

[MarkH]

5W50 describes the viscosity at two points on the viscosity/temp curve. Basically the oil behaves like a straight SAE 5 weight oil at 0 deg C and a 50 weight oil at 100 deg C. ie, its thinner when cold and thicker when hot compared to a straight 30 weight oil. Given most wear occurs at start up and a thinner oil circulates faster the bottom number is just as important as the upper one.

I'm pretty sure that almost everything I've quoted here is very much wrong.
The 5W50 oil would vary LESS in its viscosity than say a 30w40 oil and I don't know that there is any oil that has unchanged viscosity through the temperature range.

From what I understand:
5w50 oil should be the viscosity of 50 weight oil at operating temperature.
If you took 5 weight oil and lowered the temperature until you reached a certain quite cold temperature, maybe it is -40°C but I'm not sure of the actual temperature, then at that temperature the 5w50 will flow as well as the thickened (due to the cold) 5 weight oil.
I'm sure there are technical documents that describe how to ascertain the w number, but it is NOTHING like you describe.

You don't really believe that a 0w40 oil has 0 weight viscosity at 0°C do you?

Also:
Maybe think about what you typed, you think that 5W50 will be 5 weight at 0° and 50 weight at 100°?
So you actually think that it is very thin when cold and thickens when it warms up?
Surely the more you think about it the more wrong that must seem?

I believe that the w number is more about extreme cold performance than anything else, if it gets really cold where you live than maybe a lower w number would be better.
However, good quality fully synthetic oils should flow quite well at cold temperatures and in NZ we shouldn't have a problem with any of the good oils.

[MarkH]

And the belief that the higher the viscosity number the better the oil is not true.

Wow, who believes that?
I won't touch 50 weight oil because my motorcycles' manufacturers specify 40 weight oil. Similarly I wouldn't use 30 weight in them either.
I'm aware that some Honda car engines are designed to run 30 weight oil and there is a new Mobil 1 that is 30 weight (0w30) so I'd use that if I had one of those cars.
There are also some newer Honda and Toyota engines that run on 0w20 - I wouldn't run 30, 40 or 50 weight oil in those.

My belief is that you should use the correct viscosity oil for your engine.

The w number might matter, but 15w, 10w, 5w and 0w are probably all fine where I live.
I can't really see that a pour point of -39°C or a pour point of -54°C would make a huge difference to me when I've never started my bike at a temperature under -5°C.

[Flip]

I'm pretty sure that almost everything I've quoted here is very much wrong.
The 5W50 oil would vary LESS in its viscosity than say a 30w40 oil and I don't know that there is any oil that has unchanged viscosity through the temperature range.

From what I understand:
5w50 oil should be the viscosity of 50 weight oil at operating temperature.
If you took 5 weight oil and lowered the temperature until you reached a certain quite cold temperature, maybe it is -40°C but I'm not sure of the actual temperature, then at that temperature the 5w50 will flow as well as the thickened (due to the cold) 5 weight oil.
I'm sure there are technical documents that describe how to ascertain the w number, but it is NOTHING like you describe.

You don't really believe that a 0w40 oil has 0 weight viscosity at 0°C do you?

Also:
Maybe think about what you typed, you think that 5W50 will be 5 weight at 0° and 50 weight at 100°?
So you actually think that it is very thin when cold and thickens when it warms up?
Surely the more you think about it the more wrong that must seem?

I believe that the w number is more about extreme cold performance than anything else, if it gets really cold where you live than maybe a lower w number would be better.
However, good quality fully synthetic oils should flow quite well at cold temperatures and in NZ we shouldn't have a problem with any of the good oils.

The 10W40 is a way to describe the viscosity curve of a motor oil by plotting two points on the temp/viscosity graph. Modern muitigrade oils have a flatter or better viscosity curve than old mono grade oils. The 10 number refers to the oils viscosity being the same as a straight 10 weight oil at low temp, the 40 is at high temp. Yes they use 0 and 100 because it is easy to calibrate in a lab.

So the viscosity curve of modern multigrade lubes are described at two temps as having in this case the viscosity of a straight 10 weight oil at low temp and the viscosity of a 40 straight weight oil at high temp. Compared to a mono grade oil they are thinner cold and thicker when hot. How else can you discribe complex viscosity curve without a complex equasion?

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

[bmws1r]

Synthetic oils have a high polymer shear strength, have a higher stable operating temp, and tend to keep the rated viscosity for more heat cycles.

However they also flow twice as fast as the equilivent mineral oil, ie older design engines with bigger designed clearances it is not suited in some designs.

I used the shell advance range of motorcycle oils, until they stopped selling them here in NZ, no problem I'll just use shell rotella, but then they changed the formula, not suitable for motorcycles anymore.

[Voltaire]

Synthetic oils have a high polymer shear strength, have a higher stable operating temp, and tend to keep the rated viscosity for more heat cycles.

However they also flow twice as fast as the equilivent mineral oil, ie older design engines with bigger designed clearances are not suited.

I used the shell advance range of motorcycle oils, until they stopped selling them here in NZ, no problem I'll just use shell rotella, but then they changed the formula, not suitable for motorcycles anymore.

I gather that synthetic does not break down as quickly as Dino oil.
I've been running Penrite Full Synthetic extra Zinc in my 1972 BMW Racer and it gets run to 8000 RPM, seems to go ok and still on original mains.
but that's a plain bearing engine, don't know about ball or roller main motors.