We change oil (and filter, of course) every 50 hours on our C172S. The IO360 engine is now at 3100 hrs.
Maoraigh wrote:
We do 25 hour oil changes and 50 hour oil and filter. Continental O200, past TBO
Our Super Cub (90 hp Continental) from 1949 has no oil filter. The engine still lasts forever.
what_next wrote:
One more parameter is the thermal capacity of the oil reserve. In most engine installations, oil is required for engine cooling as well as for lubrication
The oil is also designed to be within a certain temperature range for proper lubrication, not too hot and not too cold or the viscosity will be off, and the oil pressure will be too high or too low..
We do 25 hour oil changes and 50 hour oil and filter. Continental O200, past TBO, and hoping to make 3000+ hours. Quick drain, and we don’t need a tube, just a plastic container supported up to it. Screw-on filter conversion.
boscomantico wrote:
Sure, but then the better question should be: why does it need 6 quarts while other engines of similar design and displacement need only 2 or 4 quarts to run properly?
One more parameter is the thermal capacity of the oil reserve. In most engine installations, oil is required for engine cooling as well as for lubrication. Depending on the size of the oil cooler and the airflow through it the quantity of oil will vary. Less oil heats up quicker (which is usually good) but will get hotter (which may not be good). I can see this even in my car – between min. oil and max. oil level the oil temperature difference is over 10 degrees C.
At work our technicians want us to keep the oil level as close to minimum as possible. This drastically (according to them by a factor of 2-3) reduces oil consumption compared to keeping the level at max. Oil temperature is no factor in these engines because there is an oil/fuel heat exchanger. Hotter oil is beneficial because it will result in hotter fuel.
I am very interested in the various comments about oil degrading after 30 ish hours.
I have a quick drain on the sump of my Piper PA28-181 it would be very easy for me to change the oil every 25 hours to prolong engine life.. I want my engine to run well past 2,000 hours in fact, I’d be happy to go for 3000 hours if it behaves properly. So far it’s at 500 hours and in very good condition. I have a hose I can pop on and I can do this job without removing the bottom cowling. I am thinking of only changing the filter at 50 hours as usual.
Can anybody see any issues with leaving the filter on at a 25 hour change?
Then: why the longer sump? 
A longer sump needs more oil for a given range of pitch angles, before the inlet to the oil pump gets unported?
Sure, but then the better question should be: why does it need 6 quarts while other engines of similar design and displacement need only 2 or 4 quarts to run properly?
The min oil requirement comes from the engine manufacturer and the certification regime requires the minimum engine oil level to be twice the amount the engine needs to operate within the approved environment (bank/pitch, etc.). The sump capacity also comes from the certification regime, it is min level + max allowable oil consumption * max endurance.
