Oil consumption increasing as oil gets older

JasonC

Experience has shown us that most Lycoming engines don’t like to be filled to the full mark on the dipstick, the full mark for the O-235 is 6 USQ and the O-360 8 USQ, we use 5.5 & 7 respectivly as the full mark and top up ( with a full sealed bottle) at 1 USQ below that level.

This policy has drasticly reduced the oil usage, I say usage because the engine does not consume the extra oil, it just throws it out of the breather onto the bottom of the aircraft.

I have had some involvement with O-540 engines and usually consider 10 USQ to be full rather than the 12 USQ on the dipstick.

I have had some involvement with O-540 engines and usually consider 10 USQ to be full rather than the 12 USQ on the dipstick.

I operate my O-540 with 5qt on the dipstick. Sump sizes depend on the exact variant of the engine. The main reason for the engine to throw oil overboard is pressurization of the crankcase through leaks in piston rings.

Achimha.

A agree totally about piston blow by being a major factor in oil consumption, I suspect that the greater air volume in the sump/crankcase gives a dampening effect on pressure variations and reduces the tendency for the oil mist to exit via the breather.

Lowering the oil level will increase the air volume in the sump/crankcase as well as decrease the likelihood of oil from the sump being thrown up into the crankcase moving parts and creating a thick oil mist that increases the volume of oil exiting the breather.

I can’t see any down side to running the engine with 5 USQ as long as the engine oil consumption is a known value, the only problem with it is if I returned an aircraft to a customer after a maintenance check with only 5USQ of oil he would think I was not doing the job properly.

It should be remembered that there is about 1 USQ of oil hiding within the oil filter and cooler so the actual oil contents of the engine is about one USQ greater than indicated on the dipstick.

A&C I agree. The argument from someone close to piper was that for certification they needed to increase the amount of oil held to show that the aircraft would run out of fuel before it consumed its oil. But the excess just blows out the breather. Between 8&10 quarts was the sweet spot.

We did find a small oil leak in the usual place (the short flexible hoses feeding the tops of the cylinder heads).

Yours has rubber oil hoses that bring oil to the valve chamber? I don’t have that, only oil return lines but they are steel. The oil to the head comes via the push rods.