Oil curiosities: pressure vs oil viscosity, too much oil in sump?

[FlyingDude]

Hello gang,

I've been noticing some things, so I wanted to share them and ask for pireps or A&P advice... 

- If I put more than 6qt in the IO360A1A of my M20E, it comes down to 6qt very rapidly.  It's like it literally sends it out.  I don't get any more oil stains in the cowls or on the nose gear than I would if there was 5.5qt, so I assume it's dumped out of the breather tube.

- In the summer, with 6qt Aeroshell W100P, oil pressure gauge is in the middle of green arc, 75psi.  With 5qt, it goes down to 60psi (green-yellow boundary)

- In the winter, with 6qt of Phillips XC 20W50, I am getting 60-65psi with 6qt and got 55psi with 5qt.  Effect of viscosity on pressure is explained here (https://www.tribonet.org/wiki/low-oil-pressure/#:~:text=Oil Viscosity%3A,leads to low oil pressure)  

- In climb, I get the 6qt pressures even with 5qt of oil in the sump.  I assume that's because oil puddles in the back of the sump, where the pump scavenges it.

- There is an oil heater probe in the oil screen plug.  I wonder if that obstructs oil flow in any way, so that it's noticeable in some cases.

All datapoints taken with clean sump screen and new filter and new oil.  Oil temperatures in green arc.

I'm undecided between testing the oil pressure gauge, adjusting the pressure relief or not doing anything.  My mech said that it's fine but I can increase the pressure if I want to...  So, I'm in the "optional" domain.

Thanks...

[FlyingDude]

13 minutes ago, Evan said:

seem to love 6 quarts. Anything over that, they tend to spit out

Lovely to hear that my engine is not a black sheep! 

13 minutes ago, Evan said:

I'd personally just run XC all year round.

Could you explain?  It gets cold here in Michigan.  --15C becomes the normal.  -5C is warm in February...  I think you need lower viscosity oil in the winter...

14 minutes ago, Evan said:

Verify the accuracy of your oil pressure gauge before cranking the pressure up

Any quick way to do that, short of sending it out?

Thanks again.

 

 

[Fly Boomer]

2 minutes ago, FlyingDude said:

Could you explain?  It gets cold here in Michigan.  --15C becomes the normal.  -5C is warm in February...  I think you need lower viscosity oil in the winter...

 

I think the point was that 20W50 is 20 in the winter, and 50 in the summer — same as your Aeroshell 100.  And when it’s not super cold or super hot, the oil is some in-between viscosity.  

[EricJ]

1 hour ago, FlyingDude said:

Hello gang,

I've been noticing some things, so I wanted to share them and ask for pireps or A&P advice... 

- If I put more than 6qt in the IO360A1A of my M20E, it comes down to 6qt very rapidly.  It's like it literally sends it out.  I don't get any more oil stains in the cowls or on the nose gear than I would if there was 5.5qt, so I assume it's dumped out of the breather tube.

- In the summer, with 6qt Aeroshell W100P, oil pressure gauge is in the middle of green arc, 75psi.  With 5qt, it goes down to 60psi (green-yellow boundary)

- In the winter, with 6qt of Phillips XC 20W50, I am getting 60-65psi with 6qt and got 55psi with 5qt.  Effect of viscosity on pressure is explained here (https://www.tribonet.org/wiki/low-oil-pressure/#:~:text=Oil Viscosity%3A,leads to low oil pressure)  

- In climb, I get the 6qt pressures even with 5qt of oil in the sump.  I assume that's because oil puddles in the back of the sump, where the pump scavenges it.

- There is an oil heater probe in the oil screen plug.  I wonder if that obstructs oil flow in any way, so that it's noticeable in some cases.

All datapoints taken with clean sump screen and new filter and new oil.  Oil temperatures in green arc.

I'm undecided between testing the oil pressure gauge, adjusting the pressure relief or not doing anything.  My mech said that it's fine but I can increase the pressure if I want to...  So, I'm in the "optional" domain.

Thanks...

What are your oil temperatures during all this?    If pressure is inversely tracking temperature then the issues may be more related to oil cooling (too much or too little) or a lazy vernatherm (oil temp regulator).

The 6qt thing is because above that level there is oil high enough in the crankcase to be subject to crankshaft windage, which aerates it so some just goes out the breather.   Usually a film on the belly or gunk on the belly antenna leading edges will show this more than usual.

I'd be cautious about cranking the oil pressure up until you're certain about what's going on.   My airplane is pretty sloppy about regulating oil temperature and under certain circumstances I'll get either high or low oil pressure alarms, so I don't really have room to adjust it either way without compromising something more than it is.    Because you're in a cold climate you'll likely have oil pressure on the high side during warmup, so that's worth paying attention to to not make it worse.

 

[FlyingDude]

47 minutes ago, Evan said:

analog gauge or digital

Analog.  The original Garwin 6-pack.

[FlyingDude]

1 minute ago, EricJ said:

What are your oil temperatures during all this?

Around 200F, in the green arc.  The second tick under the end of the green arc.

[FlyingDude]

53 minutes ago, Evan said:

To check the pressure I'd first use a known gauge that works.

Where do you get one, without buying a new one just for this purpose?  New Garwin gauges are no longer available.  The system works by sending oil all the way to the gauge, so I don't think I can use just any air pressure gauge, or can I?...

[Hank]

You. An check the vernatherm in your oil cooler by removing it, comparing the reading to ambient air then dunking it in boiling water. Ambient should be shown on your OAT and of course water boils at 212°F unless you're at altitude.

[FlyingDude]

Yeah, I was asking about how to check OP gauge.

[EricJ]

23 minutes ago, Evan said:

Curious as to why your engine is "sloppy" about regulating oil temp.

I'm in a hot climate so we have heat extremes, and then climbing to altitude in the winter can be very cold.   I think my vernatherm is a little lazy as I see oil temps around 165F sometimes during cruise at altitude in the winter.   So temps run over a wide range.    I think up north some people block the oil cooler a bit to mitigate the low temps, but down here that can be counterproductive when it gets warm.

 

[Ragsf15e]

3 minutes ago, EricJ said:

I'm in a hot climate so we have heat extremes, and then climbing to altitude in the winter can be very cold.   I think my vernatherm is a little lazy as I see oil temps around 165F sometimes during cruise at altitude in the winter.   So temps run over a wide range.    I think up north some people block the oil cooler a bit to mitigate the low temps, but down here that can be counterproductive when it gets warm.

 

@EricJknows this but I quoted him to expound on what he said, Oil coolers get gunked up and bent fins after a while too, so maybe cool less effectively when it’s hot out, but when it’s really cold, you can still see low oil temps and higher pressure.

Heres the thing, as a pilot, you’ll notice the pressure is directly related to your rpm and oil temp.  High rpm, cold temp = high pressure (like initial takeoff).  Low rpm, high oil temp =low pressure (like idle taxi after landing).  It is easy to see yellow range high and low in these conditions but the engine be working fine.

[Hank]

52 minutes ago, FlyingDude said:

Yeah, I was asking about how to check OP gauge.

The only way that I know is to add a pressure gage that you know works into the line using a T-connector. You can get fancy and use a calibrated gage, then adjust yours to match the reading if possible, otherwise just compare the numbers and write down the difference for use in flight.

Just like your compass variation card, you can create an Oil Pressure Variation card, with a lot fewer numbers!

Just be aware, as @Ragsf15e pointed out, that there is a relationship between Oil Temp and Oil Pressure. It's difficult to pump cold, thick oil through the system, so the pressure will read high; similarly, hot, thin oil pumps easily, making the pressure read low.

[FlyingDude]

4 hours ago, Hank said:

add a pressure gage that you know works

Where to find one? New one from spruce? Costly. Cheap one from AutoZone/Amazon/Harbor freight? Can you trust it? Definitely not another 40-50 year-old one from another Mooney ...

[Hank]

20 minutes ago, FlyingDude said:

Where to find one? New one from spruce? Costly. Cheap one from AutoZone/Amazon/Harbor freight? Can you trust it? Definitely not another 40-50 year-old one from another Mooney ...

Often a mechanic will have one. Needn't be an aircraft gage, one from your neighborhood auto mechanic would work, as long as it reads the numbers you want to see.

[A64Pilot]

29 minutes ago, FlyingDude said:

Where to find one? New one from spruce? Costly. Cheap one from AutoZone/Amazon/Harbor freight? Can you trust it? Definitely not another 40-50 year-old one from another Mooney ...

Get a decent cheap one, plumb it in temporarily and run the line in through the ice window, your just validating the gauge, so if your factory one was 80 PSI at 2000 RPM on the ground, and your cheapo temp installed one runs 80 PSI on the ground at 2000 RPM, in my opinion it’s validated. I don’t think you need to fly with it installed.

‘Best is to connect the factory gauge to a dead weight tester, but they aren’t real common.

You really should validate a gauge before you start adjusting things to make the gauge read good.

A major purpose of multi vis oil is for cold weather, if pressure is too high during warm up and taxi with it, then it’s likely you didn’t pre-heat enough.

Of course I know you know about blocking off some of the oil cooler for cold Wx ops, very unlikely you will find any approval to do it, but most do.

[PT20J]

7 hours ago, FlyingDude said:

Where to find one? New one from spruce? Costly. Cheap one from AutoZone/Amazon/Harbor freight? Can you trust it? Definitely not another 40-50 year-old one from another Mooney ...

I bought one from McMaster-Carr when I was troubleshooting a fuel pressure issue. Not very expensive and good quality.

[FlyingDude]

Just ordered this from Amazon. Once I’m done, they’re going into my differential cylinder leak tester project

 

 

[A64Pilot]

All our engines are “sloppy” maintaining oil temp because they don’t work like many think they do.

Most think they work like the thermostat in our car, that is block flow to the cooler until the liquid heats up, then gradually allowing fluid flow to the cooler as the temp rises and in a well operating system the thermostat never fully opens thereby holding set temp very well.

But that’s not how they work, the way a Vernatherm in an aircraft works is when oil is cold oil flows through the cooler and bypasses it, then as the oil heats up the bypass is slowly closed off making more and more oil flow through the cooler, and when the engine is warm the Vernatherm is fully closed, any more heat like say in a climb and the temp goes up because there is no way to add additional cooling.

So in cold weather for example as oil flows through both the cooler and the bypass it’s entirely likely it’s being over cooled and the airflow through the cooler has to be blocked to allow the Vernatherm to close to get to operating temp.

I’ve always wondered why there aren’t STC’s to add an adjustable air flow control so a pilot can close off some of the cooling air to the cooler in cold weather, instead we have to put duct tape or whatever on the cooler, which obviously isn’t adjustable in flight and I’m sure putting duct tape or whatever on a cooler isn’t approved, but it’s been done by so many for so long it’s just ignored.

[FlyingDude]

1 hour ago, A64Pilot said:

an adjustable air flow control so a pilot can close off some of the cooling air to the cooler in cold weather

That’s your cowl flaps! I don’t operate them purely based on climb/cruise/descend logic; rather I use them to maintain CHT. That is to say: I don’t open them during descent in the winter; but I crack them open during cruise in the summer. 

 

[A64Pilot]

3 hours ago, FlyingDude said:

That’s your cowl flaps! I don’t operate them purely based on climb/cruise/descend logic; rather I use them to maintain CHT. That is to say: I don’t open them during descent in the winter; but I crack them open during cruise in the summer. 

 

Cowl flaps control cyl head temp, but if you have flown in really cold weather then you know how it would be nice to have something similar for oil temp.

 

[FlyingDude]

11 minutes ago, A64Pilot said:

t if you have flown in really cold weather

I fly in Michigan… 

[A64Pilot]

Then you certainly should know how hard it is sometimes to get your oil temp up high enough to cook off the moisture

[takair]

On 11/23/2022 at 9:46 AM, FlyingDude said:

- There is an oil heater probe in the oil screen plug.  I wonder if that obstructs oil flow in any way, so that it's noticeable in some cases.

I am really curious about this?  Do you still have the screen in place too?  It does seem restrictive based on my picture of the geometry.  I have seen at least one Lycoming where the gasket between the sump and the accessory case was bad and would occasionally suck air and reduce oil pressure.  It would seem a restriction at the inlet might cause some level of cavitation or make it prone to having rather low pressure going tot he pump.  A leak in the gasket might make it worse.  I’m not saying this is your issue, but I am having trouble visualizing how they got a heater in this plug.  I can barely,an age inspection on one without the addition of wires and parts.  Do you have pictures or references?

[FlyingDude]

@takair That’s a legitimate question. I use new copper gaskets and torque it well, so I doubt it’s the leakage possibility. However I would have loved to mount the original plug to look for any differences.  unfortunately the heating system was installed many years before I got the plane so I don’t have it…

[takair]

7 minutes ago, FlyingDude said:

@takair That’s a legitimate question. I use new copper gaskets and torque it well, so I doubt it’s the leakage possibility. However I would have loved to mount the original plug to look for any differences.  unfortunately the heating system was installed many years before I got the plane so I don’t have it…

So, is there still a screen and is the heater within the screen?