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SAE does destructive testing meaning they put the oil in a standard "test" engine and run that engine until it disintegrates. How long that takes determines the grade given to the oil.
The grades and testing have become more and more stringent over the last 60 years.
I used to do the 3 in 10 changes until I retired from working on cars.
On the Sentra.
I use Mobil 1 advanced for high mileage engines, instead of following any specific change interval, I change it when it gets half a quart low, which seems to be working out to around 6-7500 miles based on current observations.
On my bikes.
They are all air cooled, I use Castrol synthetic. 2 quarts does the GZ250 and the 65 Honda 50. I have not had the GS500E on the road for over a year and the last change on that I used dino oil for the 1200 miles I rode that bike.
Synthetic is not better as far as efficiency, but in my opinion is better for longer change intervals in cars. I do run the Sentra through two changes on the same filter, which is supposed to be good for 15k miles anyway.
On air cooled bikes, synthetic gives you a better margin since they operate at higher temperatures that liquid cooled engines. I don't stretch out change intervals on bikes beyond manufacturers recommendations but do go two changes on filters, if equipped.
For $50 (always on sale) I get 10 quarts for the Sentra, which does 3 changes. I think the extra life filter is about 8 bucks, so that works out to $4 for the filter and $16.66 for the oil per change on the Sentra ($20.66 total).
reagrds
mech
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