Oil leaks and consumption

[GauzeGuy]

Continuing from my previous thread, I called the A&P that looked at the aircraft I flew and finally got the rest of the story. Not going to get into that here (don't feel like attracting any more trolls)...

Anyway, with that said:

1) How much oil loss or consumption is reasonable before an aircraft is no longer airworthy (assume the scenario involves a 172 with a higher timed engine)?

2) Traditionally, I've done flight planning to require a 90 minute fuel reserve. On a high time engine, should it be reasonable to expect that the oil levels would stay within a reasonable level given a 3 to 4 hour flight? Would landing more often to check oil be advisable?

3) 172N POH states 6 quarts of oil should be filled prior to take off on a longer flight. I know the aircraft can take more. Is the POH recommendation still within reason in the scenario of a higher time engine?

 

[poadeleted20]

1) How much oil loss or consumption is reasonable before an aircraft is no longer airworthy (assume the scenario involves a 172 with a higher timed engine)?

Which engine? Original Continental O-300, later Lycoming O-320, or current production Lycoming IO-360? If it's a Lycoming, their Service Instruction 1427C says "The following formula is used to calculate the maximum allowable oil consumption limits for all Lycoming aircraft engines. 0.006 x BHP x 4 ÷ 7.4 = Qt./Hr." So, for example, if the engine is the 160HP Lycoming O-320-D2J which I suspect may power more 172's than any other engine, the max oil consumption before it is no longer airworthy would be about 1/2 qt/hr (0.52, to be more exact). Don't know the Continental limit.

2) Traditionally, I've done flight planning to require a 90 minute fuel reserve. On a high time engine, should it be reasonable to expect that the oil levels would stay within a reasonable level given a 3 to 4 hour flight?

Assuming:

• Lycoming O-320-D2J
• you filled it to at least 6 qts before takeoff
• Lycoming says not to operate the engine with less than 4 qts in the sump
• max 1/2 qt/hr consumption to be airworthy

then yes, it should not fall below the minimum recommended operating level over a 4-hour flight.

Would landing more often to check oil be advisable?

If it's using that much oil that you can't go four hours without the oil level going too low, then landing the plane and not flying it again until it's fixed would be advisable.

3) 172N POH states 6 quarts of oil should be filled prior to take off on a longer flight. I know the aircraft can take more. Is the POH recommendation still within reason in the scenario of a higher time engine?

As discussed above, yes. And that 172N uses that O-320-D2J engine, so the examples above are applicable.

BTW, the Lyc O-320 has an 8-qt sump capacity, but if filled to capacity, tends to blow out a good bit of that through the breather. Typically, the O-320 will not carry more than about 6-1/2 to 7 quarts of oil without blowing it out. So, filling it more than that will give you a false impression of how much the engine is consuming. If you want to know what your engine will carry, fill it to capacity, take it flying out for half an hour or so, and then land. When the engine cools, check the oil level. Whatever you see is what it will carry, and you would be wise not to fill it above that point unless you like cleaning oil off the belly and making Aeroshell's stockholder's happy.

 

[Tony_Scarpelli]

Much oil usage can be fixed with rings, rebuilt cylinder and such so it can be a minor to not so minor repair to get the oil consumption down.

I regularly hear 1 qt per hour bandied about at most airports as allowable or the point at which the mechanic starts to get a quiz y feeling..... Of course the only way a mechanic knows what your consumption is, is if you tell him or give him a log of oil added.

I am not discounting at all, what Capt Levy has provided as authoritative.

 

[Tom-D]

IMHO any engine that uses oil to the extent that it will be below the minimum required for safe operation at the end of the flight, is using too much.

each manufacturer has their own numbers for that amount.

 

[Tom-D]

Much oil usage can be fixed with rings, rebuilt cylinder and such so it can be a minor to not so minor repair to get the oil consumption down.

I regularly hear 1 qt per hour bandied about at most airports as allowable or the point at which the mechanic starts to get a quiz y feeling..... Of course the only way a mechanic knows what your consumption is, is if you tell him or give him a log of oil added.

I am not discounting at all, what Capt Levy has provided as authoritative.

Ranger operators get worried when they use less than 2 qts per hour.

 

[JHW]

IMHO any engine that uses oil to the extent that it will be below the minimum required for safe operation at the end of the flight, is using too much.

each manufacturer has their own numbers for that amount.

that's why tiger moths owners cut out the side of the oil tank and braze on another tank to make it twice as big

 

[Ted]

Ron is correct on the Lycoming recommendation. However, that is based on a zero-leak assumption (because Lycomings never leak! ). I think it comes out to something like a quart every 6 hours for a 172 at cruise power, but it's been a while since I did the math.

Everyone has their own limit that seems to ignore manufacturer recommendations. Even when the 310 was spitting lots of oil out of the breather, its worst rate was around a quart every 4 hours. By the time it's a quart every hour on a horizontally opposed Lyc or Conti - that's a bit scary to me.

I think the Lycoming 360s hold 8 quarts of oil max. Some engines will find a happy medium of less than that. My engines tend to like 8 quarts (520s/540s). So really you need to know your engine. It should never go below the minimum, and if it's a real problem, you should land and check it more often... And fix the problem.

 

[poadeleted20]

Ron is correct on the Lycoming recommendation. However, that is based on a zero-leak assumption (because Lycomings never leak! ). I think it comes out to something like a quart every 6 hours for a 172 at cruise power, but it's been a while since I did the math.

If you're saying that it's actual HP produced rather than rated HP on which that formula is based (and knowing your background, I'll accept that as fact), then the rate for a 172N with the 160HP O-320-D2J engine at typical 75% cruise power would be 0.39 qt/hr, which translates to 1 quart in about 2-1/2 hours, not 6.

BTW, Lycoming says for minimum oil for the O-320/360-series engines with the 8-qt sumps:

• Do not to take off with less than 4 qts in the sump
• If the engine ever shows below 2 qts at shutdown, do a complete teardown inspection.

 

[Ted]

If you're saying that it's actual HP produced rather than rated HP on which that formula is based (and knowing your background, I'll accept that as fact), then the rate for a 172N with the 160HP O-320-D2J engine at typical 75% cruise power would be 0.39 qt/hr, which translates to 1 quart in about 2-1/2 hours, not 6.

Proof I haven't done the math in a long time.

But yes, brake specific oil consumption is based on the horsepower being produced, not on the rated horsepower. Obviously this makes for some estimates, but whatever your cruise power is is a pretty good estimate.