Originally Posted by Jesse
The normal/acceptable oil consumption rate is below 5 Hours per quart to upwards of 20.
More specifically it is given as a maximum in Section 3 of the Lycoming Engine Operating Manual.
It varies by power setting - for a O-360-A model -
Full rating at 2700 rpm - 0.8 qts per hour
Performance cruise (75%) - 0.45 qts per hour
Economy cruise (65%) - 0.39 qts per hour
The economy cruise number would give almost 10 qts used in a 25 hr oil change period. I would be concerned if my engines got close to that..