If you put a full 8 quarts in your average IO-550, plan on AT LEAST one quart being blown out of it in the first couple hours of flight.

Just like our old JT15Ds and our current FJ44s, the IO-550 in our Cirrus is real, REAL happy and stable at 7 quarts.

 

Actually not, as long as there is enough oil to maintain pressure and flow over the vital parts it will circulate through the oil cooler, dump it's excess heat, and then go back for another pass. The capacity of the oil to remove heat depends on how cool you can get it at the oil cooler discharge.

Extra oil beyond what is required in the loop just sits in the sump or reservoir and doesn't lose much heat there...some but not as much as the cooler.

Now that extra oil is still pretty important...it provides a buffer for burnoff and leaks so I would stick with 5-7 quarts, 6-7 for long XC. Anything over that will just blow off quickly.

Not recommending this, but I know you can fly with significantly less than five quarts on short local flights if you know the airplane and how much oil it burns. If you get a big leak a few extra quarts probably aren't going to help you, they will be below and behind you when the oil pressure gauge drops anyway.

This is for the 360, which has an 8 quart capacity and is recommended for 6-8 qts (5-8 in some airplanes).

160 HP Cessnas (320) will usually have a 7 qt. capacity, 5-7 recommended.

As always, check your POH for the right answer.