Is a little OIL knowledge dangerous

[johnvw]

Hello All,
Pardon me whilst I digest my heart pill...

I have begun educating myself in regard to OIL, essentially as to why I can / can not use car oil in my new motor cycle.
Currently I have an A4B8 audi and 2011 Vw Gti, each digesting the good stuff ( Castrol Professional LongLife III 5W-30).
MUCH TO MY HORROR I have discovered that the cSt ( centistoke ) number at 40 C is 169 ( can this be correct, surely a misprint). If this is correct just how thick is this oil at cold startup.
As a reference at 40 C
Castrol Edge 5W30............. 71
Nulon 5W-30 .................... 66
Valvoline Syn Power 5W-30...69
Modil 1 5W-30 ...................65

Dedicated BIKE oils exhibit large 40C cSt numbers also 79.5 and 98.6, 99.

WHY such large cSt numbers when low numbers ( to my way of thinking) suggest 'thinner' oil ( at low temps) for better and more efficient lubrication.

I look forward to the OIL techs as this has me baffled.
Also, any logical/technical reason car oil can not be used in the bike (dry clutch). The manual refers to SAE 10W-40 API SF / ACEA A2 or better. API SF seems a very old spec. as we now have available L and M.
Best Regards
John

[mk3pete]

maybe 169 f
cant see oil at cold value change that dramatically
using 5W or 10W as a reference would be useless,

[Diesel_vert]

Currently I have an A4B8 audi and 2011 Vw Gti, each digesting the good stuff ( Castrol Professional LongLife III 5W-30).

MUCH TO MY HORROR I have discovered that the cSt ( centistoke ) number at 40 C is 169 ( can this be correct, surely a misprint). If this is correct just how thick is this oil at cold startup.

WHY such large cSt numbers when low numbers ( to my way of thinking) suggest 'thinner' oil ( at low temps) for better and more efficient lubrication.

It's a typo.

An oil with a viscosity of 169 cSt @ 40°C and 12 cSt @ 100°C equates to a viscosity index of 35, which doesn't match up with the value provided on the datasheet.

An oil with a viscosity of 70 cSt @ 40°C and 12 cSt @ 100°C equates to a viscosity index of 169, which does match up with the value provided on the datasheet.

In addition, it would be near impossible for an oil with a viscosity of 169 cSt @ 40°C and 12 cSt @ 100°C, to have a pour point of -42°C.

Also, the low temperature cranking viscosity value for any SAE 5W oil has a maximum limit of 6600 cP @ -30°C. The Australian datasheet indicates this oil has a value of 5800 cP @ -30°C.

Also, any logical/technical reason car oil can not be used in the bike (dry clutch). The manual refers to SAE 10W-40 API SF / ACEA A2 or better. API SF seems a very old spec. as we now have available L and M.

I can't really say for sure.

It may be possible that the engine is designed in such a way, that the lubricant will only provide adequate protection through sheer film strength or thickness, hence the call for a 10W-40 oil?

A reduced SAPS & reduced viscosity (5W-30) 504/507 oil is a modern oil designed for modern engines using modern fuels. I wouldn't necessarily assume that such oils are suitable for engines that don't require them.

If it were me, I wouldn't use reduced SAPS oils (such as VW 504/507 oils) in engines not designed for them without prior approval from either the vehicle or lubricant manufacturer.

[johnvw]

Many thanks for the replies.
I do not mean to be dogmatic ( just trying to understand), but I get frustrated when I hear ( from OIL Companies) you must use this because it is for motorcycles, no further explanation.
This may well the the case, I appreciate that a oil may be developed or regarded for specific use.
Using the bike manual as a guide whilst sourcing alternative lubricants, what parameters or characteristics would be important.
Viscosity cSt at 40C
Viscosity cSt at 100C
Viscosity Index
Pour Point
What other chemical information ( assuming it is not proprietary ) that may be available should be considered.
I am yet to find clarity as to why a xW-40 is of more benefit than an xw-30.

'Oh Yes, because it is thicker and when the engine reaches working temperature the xw-30 will be to thin'.
Standard type of answer.
Well yes but when both reach working temperature are they not supposed to be very similar ( cSt 10-12), and I the xW-30 is considered to be 'thinner' would not that allow for better flow, better cooling and less pressure on the oil pump.

Perhaps I am chasing my tail needlessly, but as a SENIOR now, I hate being fobbed off by those who are supposed to know.
Enough said, I look forward to your replies always.
Regards
John

[Beer Baron]

there is no problem using car oils in your bike IF it's a dry clutch.

assuming of course it's a 4 stroke bike... you just need to be aware that even though your clutch is not in the oil bath (so no need for the friction modifiers that are put in bike oil) it is still lubricating the transmission (well most likely).

just chose an oil of the appropriate rating and appropriate grade/viscosity and you should be fine. plenty of people use high grade car oils in their ducati's etc (obviously dry clutch models only). I have used motul chrono in one of my dry clutch ducati's (996) in a pinch.

people did it as for some reason the premium bike oils where way more expensive than the premium car oils. but these days the gap has closed down a bit.