So You're a Quart Low

[Colonel Sanders]

Hold on, hold on.

Many lessons in the post above, not the least
that some instructors have no clue.

Older C172's with Lycoming engines had a full
capacity of 8 qts, which they would quickly blow
out, down to 6 qts. There is no useful reason to
ever fill them above 6 qts for this reason.

With a wet sump engine, the reservoir of oil is
directly underneat the spinning crankshaft. If
the level is too high, the crankshaft will whip
it up and it will be blown out the breather tube
onto the belly.

This is called windage and is also a measureable
source of horsepower loss. The "windage level"
is generally around 65% to 75% of the full capacity.

Yes, Lycoming says that technically you only need
two quarts to keep the moving parts wet, but we
all know that oil is useful for cooling, too.

Fun fact #1: FAR part 23 requires at least half
capacity of oil, to be legal for takeoff. So with
max 8 qts, you need at least 4 qts for takeoff.

Fun fact #2: Four-cylinder Lycomings are notorious
for unporting the oil pickup, in not very unusual
attitudes. A friend of mine saw 4,000 RPM in his
RV-8 when this happened to him in a descent. It
gets worse in a sideslip.

[Big Pistons Forever]

Fun fact #1: FAR part 23 requires at least half
capacity of oil, to be legal for takeoff. So with
max 8 qts, you need at least 4 qts for takeoff.

.

Actually the FAR requires that you have enough oil to fly to fuel tanks dry at the maximum allowable oil consumption for the engine, which for most engines is around 3/4 of a quart per hour.

For someone who just bought an airplane you will find that all engines have a happy place for their oil level. As CS noted, it is usually around 75 % of the sump capacity. A good test is to fill it to what you think is about right and do a short 15 minute flight. If he oil level goes down at all you are overfilling the oil

Finally a few engine oil level facts that a lot of people do not seem to know.

1) Hot oil expands in volume and as was noted it takes a little while for the engine oil to drain down so checking the oil immediately after shut down will only give an approximate indication of the oil level. The best time to check is with the engine cold.

2) It is essential that you wipe the flat Continental style dip sticks before looking at the level. Oil will migrate up the stick over time giving a false high indication.

3) If you are an aircraft owner write down the oil level in an unused column in the journey log before every flight A sudden increase in oil consumption should be immediately investigated by your AME.

[pdw]

So why on earth do you measure it again?

Just a confidence thing, to be doubly sure its in the ball park. The oil gauges show the pressure not the level, so just one chance to keep it right. With fuel gauges, you can glance at them anytime ...

[pdw]

Actually the FAR requires that you have enough oil to fly to fuel tanks dry at the maximum allowable oil consumption for the engine, which for most engines is around 3/4 of a quart per hour.

For someone who just bought an airplane you will find that all engines have a happy place for their oil level. As CS noted, it is usually around 75 % of the sump capacity. A good test is to fill it to what you think is about right and do a short 15 minute flight. If he oil level goes down at all you are overfilling the oil.

So yeah ... when "you're a quart low" when checking (dipstick drawn out enough to see the wet mark) and there's ~ 6 left knowing 8 is the maximum, just add the 1 and return / tighten up the cap, then throw the empty in the recycling / the measured container & funnel back home; your minute is up. It helps too when the spare oil and the funnel are not so far away.

[digits_]

2) It is essential that you wipe the flat Continental style dip sticks before looking at the level. Oil will migrate up the stick over time giving a false high indication.

How come ? And what is the maximum error you could get in that way ?

[oldtimer]

One area pilots should be careful about with Continental 6 cylinder engines is the dipsticks. My first contact was with a Cessna 180, operated on floats and skiis. The oil dipstick had 2 X's embosed on the back of the sticks to be used when the airplane was on floats and the normal front markings used when the airplane was on skiis.
The company I worked for had a Cessna 206 on the optional high larger wheels. We did an engine change and I noticed what appeared to be abnormaly high reading on the dipstick and unusualy low oil consumption so after further investigation and an oil change, I (helping the AME) dumped in 6 quarts of oil and checked the dipstick. lo and behold, the dipstick showed almost 9 quarts. I put in 3 more quarts which was where it usually ran and the dipstick showed above 12 quarts. I then went to a Cessna 185 that lived close by and compared dipsticks and they matched. So I took an engraver and remarked the dipstick. Now, oil consumtion returned to normal and at the next oil change, the dipstick showed exactly what was put in and life returned to normal. Just a bit of a heads up because this is nothing new. The Cessna 310 has dipsticks specific to each engine as does the Navajo. But what about the Cessna 180/185 which was designed on wheels but are put on floats. Do the dipsticks have different markings to compensate for the different attitude of the floatplanes?

[Big Pistons Forever]

2) It is essential that you wipe the flat Continental style dip sticks before looking at the level. Oil will migrate up the stick over time giving a false high indication.

How come ? And what is the maximum error you could get in that way ?

Capillary effect, I think. I have seen the oil indicate a full litre lower after I have wiped the stick and checked the level again. So in other words if you had just pulled the stick, looked at the oil level, stuck it back in and gone flying you would have had a litre less oil than you thought.

The Lycoming round dipsticks seem to be much less affected by this phenomenon, than the wide flat Continental type

[Big Pistons Forever]

One area pilots should be careful about with Continental 6 cylinder engines is the dipsticks. My first contact was with a Cessna 180, operated on floats and skiis. The oil dipstick had 2 X's embosed on the back of the sticks to be used when the airplane was on floats and the normal front markings used when the airplane was on skiis.
The company I worked for had a Cessna 206 on the optional high larger wheels. We did an engine change and I noticed what appeared to be abnormaly high reading on the dipstick and unusualy low oil consumption so after further investigation and an oil change, I (helping the AME) dumped in 6 quarts of oil and checked the dipstick. lo and behold, the dipstick showed almost 9 quarts. I put in 3 more quarts which was where it usually ran and the dipstick showed above 12 quarts. I then went to a Cessna 185 that lived close by and compared dipsticks and they matched. So I took an engraver and remarked the dipstick. Now, oil consumption returned to normal and at the next oil change, the dipstick showed exactly what was put in and life returned to normal. Just a bit of a heads up because this is nothing new. The Cessna 310 has dipsticks specific to each engine as does the Navajo. But what about the Cessna 180/185 which was designed on wheels but are put on floats. Do the dipsticks have different markings to compensate for the different attitude of the floatplanes?

I just saw a similar thing in the opposite direction. I was doing some training in a C 210 that a fellow had just bought. The belly was just a mess of old dirty oil inside and out. The reason became clear when we drained the oil for an oil change. The regular bucket almost overflowed before the oil stopped coming out. The problem was the oil dipstick was for a regular IO 550 not the L model which is in the 210. This model has a special oil pan with a low front and a deep well in the back to give room for the nose wheel. When we serviced the engine with 9 litres of oil the dipstick only showed 6.5. Filling it up to 9 on the dipstick would result in almost 3 liters too much which of course just gets puked out and goes all over the belly.

If you have not done so it is a worth while exercise to check the calibration of your dipstick on the next oil change.

As was mentioned all engines have a "happy" oil level wci is usually around 75 % of max capacity. Filling it above this just causes the oil to get pumped over board. A bit of experimentation will find your engine's happy place.

[sidestick stirrer]

The "ashless" description is interesting. It turns out that-due to the larger clearances and tolerances in the cylinders of air-cooled engines- more lubricating oil will make it into the upper cylinder and become part of the combustion events taking place there, than would in a liquid-cooled engine.
Automotive oils do not experience this anywhere near the same level so the oil companies can use cheaper chemicals in the additives, that turn into ash should they burn.
This ash would cause havoc in the larger quantities that would be produced in an air-cooled engine so the oil companies are forced to use more-expensive chemicals to make up the additive package.
Might be one reason why Cam Saver is so expensive. Much cheaper than a top overhaul, though...

[sidestick stirrer]

No one has mentioned the "black magic" that happens inside the crankcase-breather lines, why they should run uphill after exiting the engine before being routed down to exit at a spot that is quite specific, why they shouldn't be insulated for the first bit but should near the end. All of these characteristics will have a direct influence on the oil consumption of the engine.
But I do recall CS mentioning a long time ago why airplanes in Canada need that "whistle slot" a certain height above the exit point.
Black Magic...

[Greg87]

For the amount of work involved (you already have the cowl open, rag in hand, it takes 10 seconds!) why not check it again? Why do you check the fuel gauges after fueling if you know how much you put in? I do the same with my car, or even my lawn mower! I'm working on a CRJ now after being mostly on Dash 7 and Dash 8. The CRJ has an awesome remote fill reservoir in the aft equipment bay, it's wonderful, wish the 7 had that! Anyways, it has a sight glass and markings in Quarts, going up to 5.6 I believe. So if it's at 2.5, you figure "Okay, I'll grab 3 quarts of oil and it will be full!" After pouring 3 quarts in, it's somewhere just over 4. Not the most accurate indication. This isn't a big deal, but just shows that all markings aren't entirely accurate. I guess it's a different story if it's your own plane, or one you fly regularly, and you've come to know the little idiosyncrasies like that.

I recently spent a year working on a Dash 7, each engine had it's own happy place, had to make sure to remember where to keep them, otherwise end up wasting oil through the breather. Some engines you could fill up to the "ADD 1" mark, others you wanted to keep between the "ADD 2" to "ADD 3" marks, etc. And of course checking oils after shutdown, I thought that was just common knowledge!

Colonel Sanders, as a Canadian AME I am a little offended by being grouped in with the lazy people (again) who do substandard work. I do know that there are lazy, incompetent, scam artist AME's out there, however there are pilots that could be described the same way. There are people in every profession that fit the same bill. Then there are good ones, who know their stuff, do the job properly, and try to keep as updated in the field as possible. I try to fit the second category, and while I can't claim to know it all, I try to learn as much as I can from any experiences, mine or others. Sorry, I know this is a big tangent from the original thread, in order to avoid taking the topic in a different direction, please feel free to PM me, I would welcome the discussion.

[torquey401]

Colonel Sanders, as a Canadian AME I am a little offended by being grouped in with the lazy people (again) who do substandard work. I do know that there are lazy, incompetent, scam artist AME's out there, however there are pilots that could be described the same way. There are people in every profession that fit the same bill. Then there are good ones, who know their stuff, do the job properly, and try to keep as updated in the field as possible. I try to fit the second category, and while I can't claim to know it all, I try to learn as much as I can from any experiences ...

A big +1 to that! Mr Sanders does have some good insights, but his way of communicating them to the masses leaves a lot to be desired. His most recent post in the maintenance forum is the same.

[digits_]

What I find most interesting during the oil check, is how many people hold the greasy inside of the stick, instead of the relatively clean screw on top, which is designed to hold it.

[pdw]

Yeah, then you really don't need a rag for anything. Simply unscrew to pull up (grasping only the clean edge of the upper cap) just enough to see "a quart low", next squeezing the narrow point of the funnel in beside it for the 'add', and then wait just long enough for drip to stop, remove funnel, and tighten.

[eh3fifty]

Many turbine engines will "hide" oil after shutdown

That's exactly what the turbines in the L39
do - you check the oil level after landing.

The TPE331 engines can do that. They can hide oil in the gearbox. You just do a starter test (motor the engine) up to 15% and that will scavenge the oil back into the tank for an accurate reading. In my experience it's been rare that this happens though.