Originally Posted By: Shannow
http://www.toyota.com/owners/web/pages/parts-service/parts?categoryId=32052&partNo=part9
Quote:
Many new Toyota models are certified for a new, zero weight synthetic lubrication standard, or 0W-20. This lower viscosity oil
pumps better when cold,
Note, PUMPS, which is the xW definition, not flows.
While I agree about the difference between PUMP and FLOW with regard to the xW definitions, I think we might be a little pedantic when it comes to sharply defining these terms. A lower viscosity oil PUMPS more easily (not necessarily faster as positive displacement pumps, as Shannow pointed out are by their design constant flow machines - they pump the same volume regardless of discharge pressure.)
However, when comparing two oils, the one with the lower viscosity at any given temperature will always flow better (using the volume/time definition).
So as we get to cold temperatures, two oils which had the same viscosity at a warmer temp (you can use KV@100 or HTHS as your reference point) the one with the higher VI will flow better and pump more easily.
Originally Posted By: Shannow
Well why on Earth aren't the manufacturer's using VI as a parameter to direct the consumer to use the oil that works best, rather than the Cold Cranking and pumpability specs that are, and are defined by, the xW part of the viscosity rating ?
Why do their various oil recommendations (when they have them) have the expected ambient (starting temperature) as the selection for the xW parameter, rather than average trip length (as an approximation of percentage of time in warm-up versus operating OR starting temperature, as you've discounted both of those in your argument) ?
Once again...Viscosity Index is a dimensionless number comparing two actual physical properties, making it meaningless without first defining which of those properties that you want. And no where are manufacturers specifying VI as a performance parameter...
OEM's are indirectly recommending higher VI oils in two ways
- First by recommending synthetic fluids, the OEM is putting value on higher VI as that is the only performance characteristic which separate a Group I+II base oil from a Group III (which most marketplace synthetics are made from).
- Second by creating their own oils (the TGMO which CATERHAM loves so much is a perfect example) which have very high VIs. In a perfect world, OEM's would require that only their recommended oil be used, however competition laws prevent this from being possible.
Additionally, the trend in engine oils is continually improving viscosity performance through increased VI, this is happening at all levels of the industry, so whether you want it or not, high VI is going to happen. Most consumers don't read any specifications, or even care so OEM's and oil marketers put their message where people will pay attention.
The HVI importance is not restricted only to engine oils, it has completely dominated the hydraulic oil market and is starting to become a critical performance spec of gear oils also.
