"Michael" wrote in message
om...
zatatime wrote
I fly my bird about 50 hours per year. I was taught by an old-timer
that 50 hours was fine for oil changes and that a year was an
acceptable calendar period.

I think 50 hours is fine with a filter. When I had a plane with a
screen only, I went 25 - because the oil is not filtered as
efficiently and degrades faster. I have filters now so I shoot for
50. I don't mind going over if a trip runs long - I won't change it
on the road to keep from going over - but I've never gone to 60 and if
I know I'll go over a lot I'll change it early. I'll also change
early if I swapped a jug, because the breakin is hard on the oil.

I think the calendar period is an issue. Two things degrade oil -
heat and moisture. Heat comes from engine hours, but moisture comes
from sitting.

In the old days, 50 hours was considered fine for a screen, 100 for a
filter, and a year was no big deal. Paradoxically, the reason I think
this is no longer reasonable is that the oil is better.

It used to be that the oil degraded so quickly in use that keeping
'good' oil in the engine was not practical - you would have to change
the oil every 5-10 hours. After that - well, there wasn't that much
difference between the oil at 25 hours and 100. Of course back then,
engine TBO for the small fours was in the 1000 hour range. It's
double that now, and believe me it's nothing the engine manufacturers
changed in the design. It's mostly better lubricants.

These days, there is a LOT of difference between 25 and 100. There's
even a pretty significant difference between 50 and 100. Some people
change at 25-30 even with a filter, and while that's more often than
the engine manufacturers recommend, it's not really wrong. There is a
noticeable difference between 25 and 50. I'm just not convinced it
makes a real difference compared to the other factors involved.

Michael

Dont airplane oil filter have a by-pass in them so they dont filter 100% of
the oil?