Oil - Blow out or Consumed?

[AuntPeggy]

I've always heard that the first quart of oil just blows out while flying. My experience seems to demonstrate this, too. If I top off the oil at 8 quarts before a trip, it is down to 7 quarts after 3 hours. If I leave it at 7 quarts, it stays at that level for about 20 hours. (1974 Cessna 172)

Is this a myth?

 

[TMetzinger]

It certainly seems to happen with every IO-360 I've flown behind unless they have an air/oil separator, and even then there is still some loss.

 

[Skip Miller]

Warning! I may be propagating an old wives' tale here! But this is what I have heard.

One of the certification requirements for engines is that they must be able to operate x hours with an oil consumption of y per hour. This is to ensure that with a worst case leak or consumption, the certified engine won't run out of oil and self-destruct until y hours have passed. (Of course, worst case is a regulation-defined situation, and a catastrophic failure of the oil plumbing can ruin an engine in minutes, not hours.)

x times y equals the required oil capacity.

Now everything in aviation is a trade-off. It is easy to design an engine with a deep oil pan or even a remote oil tank like in the big radials. Deep oil pans make the engines physically bigger = not desirable. So they design the engines with a shallow oil pan making it more likely the oil will be beaten into a mist by the crank journals (Lycs) or the cam (Contis) that can blow out the breather until the level works down a bit. Just as long as the oil supply is not exhausted prior to the time specified in the certification requirement.

For what it is worth. I'd appreciate confirmation if anybody really knows.

-Skip

 

[kgruber]

I've always heard that the first quart of oil just blows out while flying. My experience seems to demonstrate this, too. If I top off the oil at 8 quarts before a trip, it is down to 7 quarts after 3 hours. If I leave it at 7 quarts, it stays at that level for about 20 hours. (1974 Cessna 172)

Is this a myth?

It depends.

Some of the newer Continentals, like my IO-520D use no oil at all. I NEVER add a quart. At 25 hours I change the oil and put 12 quarts in. It just stays there.

I do get about 6 drops of oil out the breather after putting the airplane in the hangar

 

[ScottM]

I've always heard that the first quart of oil just blows out while flying. My experience seems to demonstrate this, too. If I top off the oil at 8 quarts before a trip, it is down to 7 quarts after 3 hours. If I leave it at 7 quarts, it stays at that level for about 20 hours. (1974 Cessna 172)

Is this a myth?

Peggy I fly with an O320 and I get exactly the same thing as you. Sometime I wonder if it would jsut be easier at oil change times to put the 7 quarts into the oil filler tube and spray the 8th on the belly right away.

 

[poadeleted20]

The Lycoming O-320/360 series engines are notorious for blowing out anything over about 6-1/2 on the dipstick. Thus, Aunt Peggy's experience is fairly typical, and it's why I only pour in 7 quarts when changing the oil and filter, and add oil at 1/4-1/2 qt increments between 6 and 6-1/4 indicated.

 

[Bill]

The Lycoming O-320/360 series engines are notorious for blowing out anything over about 6-1/2 on the dipstick. Thus, Aunt Peggy's experience is fairly typical, and it's why I only pour in 7 quarts when changing the oil and filter, and add oil at 1/4-1/2 qt increments between 6 and 6-1/4 indicated.

Our mechanic has similar advice for our IO360, always depart with 6qts showing on the dip stick, and you'll be fine. We too add in 1/4, 1/2, whatever increments that bring us to 6qts at departure.

 

[KennyFlys]

Definitely not a myth by my observation. The previous FBO had someone who started nonsense about oil being "between six and eight quarts." That meant they were filling it to eight on the dipstick. I put an end to it and was thought the bad guy by the front desk people who had saying otherwise. Oil usage went down drastically when I specified to not add a quart until down to just below six quarts showing. My current school has the same policy.

 

[Dave2]

O-360 here with the same results. If I run at 2550 rpm or above I can't keep anything over 6 quarts in the engine. At oil change I put in 7 qts. 6 for the engine, approxomately .5 for the filter and the rest to keep the belly lubricated.

 

[Steve]

The owner's manual for my plane (IO-540) lists oil capacity as 10-12 qts for "normal" flight and 6-9 qts for "aerobatic" flight. It seems to like 10 qts best.

 

[Stache]

All aircraft engines are designed to burn or loose some oil it’s the nature of the beast so to speak. If an aircraft engine did not use any oil I would be a little concerned. The cylinders expand at different rates and will loose or burn oil until all the cylinders are at normal operating temperature.

Some owners I know will add some mineral oil after break in. This is not recommended.

Straight mineral aviation oils are marketed primarily for use in the break-in period for new or rebuilt engines. The primary reason for breaking-in an engine on mineral oils is that they do not contain any cleanliness additives.

The lack of a cleanliness additive allows for significantly more iron filings and other debris to remain in the ring belt area. This act as lapping compounds and increase the wear rate in the compression ring/cylinder wall interface. This results in a mechanical mating or “seating” of the rings. This was especially critical with the old hard or channel chrome cylinders. A to clean engine will loose oil past the rings.

There are still a few applications where the use of a mineral oil for the entire life of an engine is recommended.



Below are several reasons for high oil usage as follows:

• Improper grade of oil.
• Failure of new rings to properly seat.
• Failed or failing bearings.
• Incorrectly installed piston rings, worn piston rings, glazed or excessively worn cylinder barrels.
• Worn valve guides.
• Oil being siphoned from engine in flight. Verify the oil filter cap is secure and that the oil access door closes properly. Verify that the breather hose is cut properly and located to prevent siphoning in accordance with the airframe manufacturer's installation procedures.
• Oil level too high do not fill above the maximum oil sump capacity.
• Expander in oil control ring improperly installed or lost its tension.
• Turbocharged engines-Oil passing through turbocharger seals.