The Cessna 120-140 Association Forum

What are those running C-85s typically seeing for oil consumption?

Not a C85, but my C90-14F burns/leaks about 1/2qt per 15hrs. Oil is changed every 15hrs. About 1100 SMOH and 800 on Millenium cylinders.
Josh

i go through a quart in the 6-7 hr range realistically. i usually add 2-2.5 quarts in a 25 hour oil change period, but start full and usually its down a quart at the end.

engine has 1550 hrs on it, cylinders all around 500 hrs. C-85. i've attacked all signs of leakage, replacing gaskets on oil cooler pad, oil tank, starter clutch, and replacing a set of pushrod tubes.

Thanks all. Time to address the leaking pushrod seals, maybe do a top while at it. 800 hours on cylinders of unknown providence seems to speak to a nice new set of Superior cylinders.

I am thinking my little 85-12 burns through a quart every 6-7 hours also -nothing really leaking. Oil gets dark pretty quickly after an oil change so i assume there could be some blow-by past the rings, but it develops full power and runs really nicely.

edidin wrote: ↑Sat Apr 29, 2023 9:17 am Thanks all. Time to address the leaking pushrod seals, maybe do a top while at it. 800 hours on cylinders of unknown providence seems to speak to a nice new set of Superior cylinders.

Realgasket pushrod tubes do not require cylinder replacement...unless you have a good reason to change the cylinder too

You might look and see if you have drilled rocker arms on the intake valves. The extra oil might be drawn into the intakes due to suction. Plugged or undrilled rockers can make a notable difference in oil consumption.

Just some "base line information" you may already have:
Continental says the "average" oil consumption is 1/4 pint/hour, or a quart in 8 hours.

They also describe a very specific procedure for determining oil consumption in Table XXII of the overhaul manual. The maximum allowed for the C85 is .35 lbs/half-hour. That works out to about a gallon in 10 hours or a quart in 2.5 hours.

So, even if your oil consumption so as high as a quart in 2.5 hours, and there's nothing else wrong with the engine, and you make sure you have enough oil on board when you start the flight, you're still good to go.

Thanks John. There's likely a top overhaul in my future, though I am still somewhat better than the maximum burn allowed as well as somewhat worse than what would like to see.

6298 wrote: ↑Sun Apr 30, 2023 3:53 pm You might look and see if you have drilled rocker arms on the intake valves. The extra oil might be drawn into the intakes due to suction. Plugged or undrilled rockers can make a notable difference in oil consumption.

how much of an effect do you notice with a drilled intake rocker? i looked through some photos from when i did the pushrod gasket stc and am pretty sure my intake rocker on at least one cylinder is drilled.