Ralfyguy,
"Mortal Low" is when you use the vertical method but get real slack about doing the check (or your bike finally starts using oil and you didn't catch that it first started) and when you do do the vertical check you don't see any oil in the window at all.
aw shite !!When you do go do the vertical Road Runner check and find you have to add nearly a quart of oil then you have been running at "Mortal Low" levels and have likely been sucking some air at the oil pump when you hit the brakes, etc and rocked the oil mass forward away from the pump intake.
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Now, why do our bikes just suddenly start using oil? We have had enough instances of pistons getting sudden galling (which puts the rings in a groove bind and causes mild smoking) to say we have that as an occasional issue that we can certainly point at.
This is an "any mileage" issue completely apart from the 45,000+ piston slap which is pure and simple wear over time.
May I propose a theory for this sudden galling -- Serobot's Theorum, with some practical expansions.
Serobot (who has written the definitive Tech Post on the subject) theorizes that:
1/3 of the folks on the list have had a vac petcock go bad on them
1/3 of the folks who are just waiting for it to happen to them,
1/3 of the folks who (because of how little and how slow they ride) may never have it happen to them. They never exceed the vac petcock trickle flow rate.
My extension on his theory is simple -- those that ride hardest will have the vac petcock starve their engine at speed and when their float bowl level gets low their mixture leans out which can cause their piston to overheat and gall or to cause rapid piston wear.
(or you name the screw up that flows from it, none of them are good news)
So, I say sudden onset oil consumption has an assignable cause -- that you had a vac petcock event at speed and "running lean" damaged your engine some.
Now, for reluctant confirmation of this theorum, we suggest a person who is a high speed rider, who has two Savages that both became NOTORIOUS oil users, who investigated oils in great detail to see if he could relieve his problems and he freely admits he has had high speed vac petcock episodes before that caused him to replace hoses multiple times and to put rebuild kits into his vac petcocks.
Note: he has recently totally rebuilt one of his engines twice and it is currently in great shape.
He now has a virgin test bed and as of now he is on alert to this potential oil consumption root cause.
Verslagen, when your rebuilt vac petcock craps out on your fresh engine bike for the very first time, keep a lookout for sudden onset oil consumption to follow soon thereafter.