Looks like what I thought was a disaster may not be a disaster after all.
Oil usage seems to have somewhat stabilized. I may get a year or more out
of this puppy before it gets unmanageable.
I think I can fairly safely say that ambient temperature has little to do
with consumption. I think I can also fairly safely say that the oil level
drops pretty much linearly on the stick, so it's not important where the
level starts and ends.
What does seem to have a very large effect on oil consumption is the manner
in which the car is driven: The more heavy acceleration, the more wide-open
throttle, the more oil the engine will consume. During the last few tests,
I have made a conscious effort to drive like a granny (sort of), and it
would appear at this point that oil consumption has dropped accordingly.
As an aside... Some observation of our Tercel has led me to the same
conclusion: The Tercel uses far more oil travelling the hills of
Pennsylvania than it does in the much flatter lands at home north of there.
The Tercel uses oil at about the rate of 6,000 miles per quart, but then it
only has about 125,000 miles on it.
Interestingly, in the face of obvious signs of heavy oil usage (wet
throttle body, etc.), my gas mileage is completely unchanged from previous
years (when the throttle body was dry). At the moment it's about 28mpg.