Oil level

[PT20J]

Here’s an early M20J

Here’s a lat M20J

[Ragsf15e]

14 minutes ago, PT20J said:

Here’s an early M20J

Here’s a lat M20J

Also, I reread the lyc manual.  As usual, you were correct at “2 qts minimum” however I start to see squirrelly things happening below about 5.5ish (or maybe it’s just that I watch closer), so I just make sure it’s always at 6 before takeoff.

[laytonl]

I run mine at 7 max, 6 min.  Below 6 qts, the oil pressure gauge tends to read like a oil level gauge with the oil pressure going below 70 psi at 6 qts and descends as the oil level decreases.  At 65 PSI I will have 5.5 qts.  I’ve noticed this phenomenon for the 10 years I’ve owned the airplane.  I’ve never owned another airplane that did this.  Lee

[A64Pilot]

17 minutes ago, laytonl said:

I run mine at 7 max, 6 min.  Below 6 qts, the oil pressure gauge tends to read like a oil level gauge with the oil pressure going below 70 psi at 6 qts and descends as the oil level decreases.  At 65 PSI I will have 5.5 qts.  I’ve noticed this phenomenon for the 10 years I’ve owned the airplane.  I’ve never owned another airplane that did this.  Lee

It’s not uncommon, in fact it is what should be happening. The same amount of heat has to be carried away by the oil regardless of the amount of oil. so the less oil there is, the less there is to carry the same heat, so it’s hotter. Hot oil loses its viscosity and therefore pressure will drop with viscosity.

I know I’m going to start another you don’t know what your talking about fiasco, but here goes.

Our engines and actually pretty much all engines are more oil cooled than air or water cooled. It’s actually really only the heads that are air cooled, everything else is oil cooled. The cylinders don’t actually get very hot and yes they are primarily air cooled. The cylinders are more of a heat sink for the heads than get hot themselves

But the camshaft, the crankshaft and everything else in the engine case and accessory case is oil cooled and the oil is air cooled, so in point of fact all engines are air cooled, except boat motors if you look at it that way.

‘But my point is that oil carries a significant amount of heat away, it’s an important cooling medium

Edited March 21, 2021 by A64Pilot

[PT20J]

Our engines are air cooled. The cylinders are cooled by air as is the oil. From a thermodynamic standpoint, the oil is a working fluid to carry heat to the oil cooler where the heat is transferred to the cooling medium which is air. The relative amount of heat carried off the engine by the oil versus the cylinders and cylinder heads can be estimated by comparing the cooling surface area of the oil cooler to that of the cylinder/head fins. The oil primarily cools the rotating parts and helps cool the pistons. About half the rotating friction comes from the piston rings which is transferred as heat to the cylinders and cooled by passing airflow.

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[carusoam]

Don’t forget the oil flowing past the exhaust valve stems... right at the cylinder head...

They probably are the hottest engine part we have, and they are oil cooled...

Until the oil flow gets choked off from carbon build up... 

 

As far as oil cooling goes...  related to the oil level....

The oil cooler won’t notice how low the oil level goes in the sump... 

The difference will be the surface area of the oil pan covered with the extra oil... including the intake tubes that cris-cross through the oil sump on some engines... and the airflow past these surfaces...

PP thoughts only...

Best regards,

-a-

[A64Pilot]

Your cars and trucks are air cooled too.

Yes they have radiators full of coolant, but what cools the radiator? Point that out to someone with a Rotax and see how confused they become

 A not insignificant amount of heat is carried away by oil in any four stroke motor, just saying oil is an important coolant too,  to say nothing of turbo’s that’s why we have an oil cooler, and low oil level usually will mean hotter oil.

The oil cooler won’t “know” there is less oil. it remains full, but the same amount of heat will be carried to the oil cooler with less oil, dumping the same amount of heat into less fluid raises its temp.

Edited March 22, 2021 by A64Pilot

[PT20J]

37 minutes ago, carusoam said:

Don’t forget the oil flowing past the exhaust valve stems... right at the cylinder head...

They probably are the hottest engine part we have, and they are oil cooled...

Actually, the exhaust valves are cooled by conduction from the valve head to the seat and the stem to the guide. The oil can’t take the heat. This picture is of a radial engine head, but Lycoming and Continental are similar (except Continental uses solid exhaust valves). Note the amount of cooling fin area around the exhaust valve compared to the intake valve.
 

[Don Heene]

Mine is a o-360 and anything over 6 Qts. ends up on the belly.  

[A64Pilot]

25 minutes ago, PT20J said:

Actually, the exhaust valves are cooled by conduction from the valve head to the seat and the stem to the guide. The oil can’t take the heat. This picture is of a radial engine head, but Lycoming and Continental are similar (except Continental uses solid exhaust valves). Note the amount of cooling fin area around the exhaust valve compared to the intake valve.
 

Yes, all exhaust valves are primarily cooled by transferring heat to the head, well except for flat head motors of course, they transfer heat to the block. but there is some oil cooling, just not a whole lot.

But the head is partially cooled by oil, as you said the oil can’t take the heat, so enough oil has to be pumped though the head so that the oil doesn’t stay in there long enough to coke, if it just sat there it would.

As there is oil flow, and as the head is about the hottest thing in the engine, up to and sometimes even over 400F, and oil is about half that, it will pick up significant heat.

There isn’t as much oil flow as we might think though, it’s not much more than a dribble.

Just like pistons, most of their heat is transferred to the cylinder, but many pistons get significant cooling from the oil. many engines spray oil onto the bottom of the piston solely to oil cool them.

Then turbo’s the center section anyway on aircraft turbo’s is oil cooled.

‘Just saying oil is a coolant too, not just a lubricant.

‘On edit, the primary reason for what seems like excessive cooling fins around the exhaust is to cool the exhaust portion of the head, that is a very hot area as of course all of the heat from combustion passes through there, the fins aren’t for valve cooling.

Edited March 22, 2021 by A64Pilot

[GeeBee]

Bring this back up because on my IO-550 has a strange oil stick

When I pull the stick it after letting it sit over 12 hours the oil level will be 7.5 or 8. Then I wipe the stick with a rag, re-insert it, lock the cap, then pull it out again and it reads 5.5. What's with that? Which one is correct?

 

[A64Pilot]

The second one most likely.

‘My C-85 does that trick too, and it took me awhile to figure it out, on the C-85 the rather large tube that the stitck goes into extends into the oil tank, and its opening is under the oil level.

‘The dip stick has a good air tight seal, so what happens is when you shut down, it’s hot and as the trapped airspace cools off if forms a slight vacuum that will pull oil up into the tube, giving a false high reading.

‘So you have to remove the dip stick, wipe it off and re-insert it to get the true oil level, and it will likely be much lower than just pulling the stick out and looking will indicate.

Now I do not know that’s what’s going on with your 550, but I do know that the best way to check any engine is to remove the stick, wipe it clean, reinsert it and check.

 

Just remembered the Yanmar 4JHE in my sailboat was the same way, on boat motors they run the dipstick tube to the bottom of the oil pan so that you can use it to suck the oil out to change oil, and it did the same thing as my C-85

Just threw the sailboat motor in as an example, not trying to say it has anything to do with aircraft engines

Edited April 12, 2021 by A64Pilot

[GeeBee]

What you say makes sense. However the thing I don't understand is the breather tube connect to the cap tube, just below the cap, so it should vent, not form a vacuum. 

 

[A64Pilot]

Well the first reading is incorrect, as it can’t be replicated.

Possibly a argument could be made that oil i’s draining out of the prop or something if it increased level over time and stayed that way.

‘But I’m assuming your only high reading is the first one, when you remove the stick, and all further measurements are lower?

Other than the cooling thing forming a vacuum and pulling oil up the tube, I can’t come up with a logical reason the perceived oil level is higher than actual.

However I would still go with the remove the stick, wipe it off and check it indicated level, and not the original higher level as I assume it’s not repeatable.

Could always call Continental, I’ve heard they have a good service desk? Whatever they say is what I would go by, even if proves  me wrong

Edited April 12, 2021 by A64Pilot

[carusoam]

After running the engine... there is so much oil on the walls of the tube twisting the oil ‘stick’ in often scrapes oil onto what you are trying to read...

Often, an immediate reading is typically a quart low compared to a day later...

The oil cooler has a tendency to drain overnight...  a challenge you find when you add a quart after flying...  on the following day, it looks like you have overfilled the sump...

ooops...   PP thoughts only, not a mechanic...

Best regards,

-a-