Regarding multigrade; I understand "long chain polymer molecules, can get sheared into shorter bits" and then the oil reverts to the W side, but have also read: "The polymer additives do break down from thermal and mechanical degradation as the oil ages and wears out. This results in increasing the carbon build-up (sludge)." naturally go's on with why timely oil changes are important.
What are your thoughts on this?
Sludge formation can occur with monograde oils too; it's not particularly influenced by the presence of viscosity improvers. It's actually due to oxidised components of the oil, and combustion by-products, forming small [initially non-filterable size, i.e. <30 micron] particles.
Modern engine oils handle this by using detergent/dispersant additives, to keep the particles suspended in the oil, so that they are removed when the oil is drained. Many viscosity improvers are dual-function, i.e. they have dispersant properties too.
It's these particles that become sludge, when the dispersancy capacity of the oil is exhausted, and they start to stick to surfaces inside the engine. This can be easily avoided, simply by changing the oil before this point is reached. Here's an
awful example.
For engines up to smaller truck size, the most cost-effective way to manage this, is to change the oil on an distance/hours of service or elapsed time basis.
For heavy truck engines and larger, the cost of an oil change makes it economic to have the oil tested periodically, to determine its fitness for further service, and schedule changes accordingly. Sometimes the tests are used to determine additive replenishment requirements too, if the volume of oil is large enough to make this economic. This is the main reason why the heavy equipment majors [Caterpillar, Komatsu etc.] offer an oil testing service to their customers, usually run in-house, or even worksite-based. Other tests that are run routinely provide early warning of abnormal wear and oil contamination [dirt/coolant/fuel/soot], as a bonus.
Back to the B&S oil, the MSDS for it on the Victa website says that it's manufactured by Valvoline, for the Oz market. The only spec mentioned on the label is API SG/CD.
I'd say that Penrite would be a bit better product, as they do a good job on lubes for these small-volume market niches, as a rule.
And as you say, it's easy to get from the auto parts chains, at a reasonable price.
