IO360 Low oil pressure on cruise (55psi)

[redbaron1982]

So, I need to adjust the pressure relief valve to increase the oil pressure while cruising to around 70-75 psi, now it's around 55psi when cruising at 65%.

I was reading the Lycoming IO 360 maintenance manual and doesn´t give any hint on how much to adjust the pressure relief valve, meaning, I don´t know if I should do 1 turn, half turn, 2 turns, whatever.

I know this is an iterative process, but would like to get as close as possible in my first attempt. Does anyone know how much the oil pressure increase/decrease with each full turn of the pressure relief valve adjustment screw?

[carusoam]

7 minutes ago, redbaron1982 said:

So, I need to adjust the pressure relief valve to increase the oil pressure while cruising to around 70-75 psi, now it's around 55psi when cruising at 65%.

I was reading the Lycoming IO 360 maintenance manual and doesn´t give any hint on how much to adjust the pressure relief valve, meaning, I don´t know if I should do 1 turn, half turn, 2 turns, whatever.

I know this is an iterative process, but would like to get as close as possible in my first attempt. Does anyone know how much the oil pressure increase/decrease with each full turn of the pressure relief valve adjustment screw?

I can think of two resources that may have answers for this… as well as all of the mechanics on MS….

let’s invite @jetdriven and @M20Doc to see who is around on Sunday night? (Oil pressure adjustment, M20J)

Best regards,

-a-

[PT20J]

Make sure the gauge is accurate first.

[redbaron1982]

1 minute ago, PT20J said:

Make sure the gauge is accurate first.

It is, both GI 275 and the original analogue gauge indicate the same value.

[Ragsf15e]

1 hour ago, redbaron1982 said:

It is, both GI 275 and the original analogue gauge indicate the same value.

That’s significantly lower than most of them… are you sure that’s the problem?  Possibly it’s got something stuck in the relief valve, blocking the intake or another issue, but that would definitely have me looking into a cause vs just trying to turn it up?

[redbaron1982]

The recommendation from Savvy was to adjust the relief valve, so that's why I'm going in that direction. But open to other ideas.

The pressure goes higher when cold or during take off when full power is applied.

But as the oil warms up and power is reduced to ~65% then oil pressure slowly reduces 55 - 57 psi.

[PT20J]

How long since the suction screen was checked? It can get plugged up with carbon and restrict the flow.

The oil pressure relief valve can get some small piece of junk caught in it that keeps the ball from seating. According to instructor for the Lycoming factory class, 90% of pressure problems can be corrected by replacing the spring and staking the ball in the valve. Lycoming also has a service instruction 1172

[EricJ]

13 minutes ago, redbaron1982 said:

The recommendation from Savvy was to adjust the relief valve, so that's why I'm going in that direction. But open to other ideas.

The pressure goes higher when cold or during take off when full power is applied.

But as the oil warms up and power is reduced to ~65% then oil pressure slowly reduces 55 - 57 psi.

What is the oil temperature when the pressure goes down?    High oil temps will naturally make the pressure lower. 

Even if the GI275 and the OEM gauge agree, I'd triple check the gauge accuracy with external instruments for both oil pressure and temperature before adjusting anything.

And +1 to also check the suction screen.    There are a number of things to check before adjusting the relief valve, not that that's a big deal, either, but you may just be masking a symptom of something else.

 

[ArtVandelay]

How long since the suction screen was checked? It can get plugged up with carbon and restrict the flow.
The oil pressure relief valve can get some small piece of junk caught in it that keeps the ball from seating. According to instructor for the Lycoming factory class, 90% of pressure problems can be corrected by replacing the spring and staking the ball in the valve. Lycoming also has a service instruction 1172

As a crossover from another thread, this might be a job for MMO.

[N201MKTurbo]

One turn should be a good start.

[Browncbr1]

If you have a guppy mouth, you can reach in there with a crow’s foot in your fingers and adjust.   Iirc, 1/2turn (3 nut flats) is only a few psi difference.  

[redbaron1982]

9 hours ago, EricJ said:

What is the oil temperature when the pressure goes down?    High oil temps will naturally make the pressure lower. 

Even if the GI275 and the OEM gauge agree, I'd triple check the gauge accuracy with external instruments for both oil pressure and temperature before adjusting anything.

And +1 to also check the suction screen.    There are a number of things to check before adjusting the relief valve, not that that's a big deal, either, but you may just be masking a symptom of something else.

 

The temperature was between 175F and 180F. The GI 275 gauge is new (the previous one was INOP), and the OEM is a completely independent system. How likely is it for two systems without any common parts from different manufacturers to fail in the same way? I think the odds of that happening are extremely low. Or am I missing a relatively common failure mode that could affect both gauges?

Does anyone know where I can download de Service Manual for the Lycoming IO 360? I have the Maintenance Manual, but cannot find the service one, I'm starting to doubt of my Googling skills.

[Jpravi8tor]

I'm fairly certain I uploaded the service manual to Mooneyspace previously

Lycoming O-360 service manual.pdf

[EricJ]

2 hours ago, redbaron1982 said:

The temperature was between 175F and 180F. The GI 275 gauge is new (the previous one was INOP), and the OEM is a completely independent system. How likely is it for two systems without any common parts from different manufacturers to fail in the same way? I think the odds of that happening are extremely low. Or am I missing a relatively common failure mode that could affect both gauges?

My understanding of the GI-275 is that it has multiple pins for interfacing various transducers.   So it depends entirely on how yours was installed and it appears possible that it was wired in parallel with your existing transducer, i.e., the same transducer may be driving both instruments.    I wouldn't assume anything just because you have a new instrument installed.   The first step is still to verify that the instrument(s) are reading correctly.   I'd check to see whether the GI-275 has a separate oil pressure transducer from the stock instrument.   

Edit:   Just to add a little bit, the GI-275 installation manual has a procedure for adjusting the marks on the instrument, but not a calibration procedure that I can find.    It may be possible that it was just adjusted to match the existing gauge, in which case it would match the existing gauge.   

 

2 hours ago, redbaron1982 said:

Does anyone know where I can download de Service Manual for the Lycoming IO 360? I have the Maintenance Manual, but cannot find the service one, I'm starting to doubt of my Googling skills.

There may not be one.   Lycoming has Operator's Manuals and Overhaul Manuals.   The Overhaul Manuals get referenced a lot.

[A64Pilot]

I need one of those balls, to make a staking tool

[N201MKTurbo]

3 minutes ago, A64Pilot said:

I need one of those balls, to make a staking tool

What would you be staking? The pressure regulator must leak to do its job. If you cannot get enough oil pressure, it must be leaking somewhere else.

[DCarlton]

When I had high OT and low OP issues during cruise (IO360A1A), we tried many things over several years.  If I remember correctly, we overhauled the oil cooler, reseated the vernatherm valve, adjusted the pressure regulator, tried multi-weight and single weight oils to see which worked best, even installed a fixed center cowl flap (I was flying in AZ desert temps a lot).  Can't remember if we checked the suction screen but I'm guessing we did.  Got used to climbing and cruising in the upper edge of yellow.  Finally overhauled the engine for other reasons and magically, all the temps and pressures have been perfect ever since.  So.... what would have been the remaining potential causes?  Oil pump or ??? 

[redbaron1982]

49 minutes ago, EricJ said:

My understanding of the GI-275 is that it has multiple pins for interfacing various transducers.   So it depends entirely on how yours was installed and it appears possible that it was wired in parallel with your existing transducer, i.e., the same transducer may be driving both instruments.    I wouldn't assume anything just because you have a new instrument installed.   The first step is still to verify that the instrument(s) are reading correctly.   I'd check to see whether the GI-275 has a separate oil pressure transducer from the stock instrument.   

The transducers are not in parallel, I have two different transducers, one connected to the OEM oil pressure gauge and the other to the GI 275. When the GI 275 was INOP, the OEM was working. I personally (with the supervision of an AP) changed the oil pressure transducer for the GI 275, so I know that the only thing in common between the OEM and the GI 275 is the hose with the tee at the end where both transducers connect.

Usually oil pressure transducers are not "field" calibrated. They get calibrated in the factory and they deliver they mV or mA signal based on the datasheet, without any field calibration required.

 

 

[JimB]

15 hours ago, redbaron1982 said:

So, I need to adjust the pressure relief valve to increase the oil pressure while cruising to around 70-75 psi, now it's around 55psi when cruising at 65%.

I was reading the Lycoming IO 360 maintenance manual and doesn´t give any hint on how much to adjust the pressure relief valve, meaning, I don´t know if I should do 1 turn, half turn, 2 turns, whatever.

I know this is an iterative process, but would like to get as close as possible in my first attempt. Does anyone know how much the oil pressure increase/decrease with each full turn of the pressure relief valve adjustment screw?

Can I just ask if this was a gradual decrease in oil pressure or was it all at once? Seems a bit odd for it to get that low during cruise before anyone noticed or did anything about it. 

[EricJ]

40 minutes ago, redbaron1982 said:

The transducers are not in parallel, I have two different transducers, one connected to the OEM oil pressure gauge and the other to the GI 275. When the GI 275 was INOP, the OEM was working. I personally (with the supervision of an AP) changed the oil pressure transducer for the GI 275, so I know that the only thing in common between the OEM and the GI 275 is the hose with the tee at the end where both transducers connect.

With the tee it should be straightforward to connect a known good gauge and verify pressure.

40 minutes ago, redbaron1982 said:

Usually oil pressure transducers are not "field" calibrated. They get calibrated in the factory and they deliver they mV or mA signal based on the datasheet, without any field calibration required.

The display may need to be properly configured (or at least matched) to the transducer, though.   There's a list of different transducers that can be used with the GI-275, with different voltage ranges and different inputs for the GEA24 or 110.   There may still be opportunities for misconfiguration.   While I agree that with separate transducers the likelihood of error decreases, imho there's still reason to verify they're both correct before adjusting the relief valve on the engine.  

[PT20J]

2 hours ago, N201MKTurbo said:

What would you be staking? The pressure regulator must leak to do its job. If you cannot get enough oil pressure, it must be leaking somewhere else.

The ball to the seat. If that doesn't work, there is a procedure to lap the seat I believe.

[redbaron1982]

1 hour ago, JimB said:

Can I just ask if this was a gradual decrease in oil pressure or was it all at once? Seems a bit odd for it to get that low during cruise before anyone noticed or did anything about it. 

This is the trend:

This is in the last 18 months. The outlier that is showing a high value is when the transducer broke. Also, the third dot from the right was after 5 months of the aircraft being grounded, and the last one was after 10 months since the last "long" flight.

I don't know in this "inactivity" period what could have happened to cause this. Maybe I could start cleaning the oil screen and inspecting the relief valve to make sure it's not stuck.

 

[PT20J]

2 hours ago, EricJ said:

My understanding of the GI-275 is that it has multiple pins for interfacing various transducers.   So it depends entirely on how yours was installed and it appears possible that it was wired in parallel with your existing transducer, i.e., the same transducer may be driving both instruments.    I wouldn't assume anything just because you have a new instrument installed.   The first step is still to verify that the instrument(s) are reading correctly.   I'd check to see whether the GI-275 has a separate oil pressure transducer from the stock instrument.   

Edit:   Just to add a little bit, the GI-275 installation manual has a procedure for adjusting the marks on the instrument, but not a calibration procedure that I can find.    It may be possible that it was just adjusted to match the existing gauge, in which case it would match the existing gauge.   

 

There may not be one.   Lycoming has Operator's Manuals and Overhaul Manuals.   The Overhaul Manuals get referenced a lot.

There is no such thing as a Lycoming service manual. Traditionally, Lycoming produced an overhaul manual, an operator's manual, and all additional information was contained in service literature (letters, instructions, bulletins). Many, many years ago, the FAA mandated a requirement to create maintenance manuals that included airworthiness limitations. Because of the shear number of products involved, Lycoming got the FAA to delay the requirement. A few years ago, the FAA finally made Lycoming begin creating maintenance manuals, but they are only available for some later models. The only IO-360 maintenance manual that I'm aware of is for an IO-360-N1A. It's probably very similar to what a maintenance manual for an IO-360-A3B6(D) would be if there was one, but there may be differences. I believe that the overhaul manuals must be purchased, perhaps with a subscription. 

[EricJ]

38 minutes ago, PT20J said:

There is no such thing as a Lycoming service manual. Traditionally, Lycoming produced an overhaul manual, an operator's manual, and all additional information was contained in service literature (letters, instructions, bulletins). Many, many years ago, the FAA mandated a requirement to create maintenance manuals that included airworthiness limitations. Because of the shear number of products involved, Lycoming got the FAA to delay the requirement. A few years ago, the FAA finally made Lycoming begin creating maintenance manuals, but they are only available for some later models. The only IO-360 maintenance manual that I'm aware of is for an IO-360-N1A. It's probably very similar to what a maintenance manual for an IO-360-A3B6(D) would be if there was one, but there may be differences. I believe that the overhaul manuals must be purchased, perhaps with a subscription. 

There's an IO-360-P1A manual available on Lycoming's site now, too. 

There are a bunch of relevant Lycoming overhaul manuals available in the wild, arguably the most useful of which is the "Overhaul Manual Direct Drive Engine" document, which essentially covers everything without a gearbox.    Getting the latest version of something might be more difficult, but I've been able to find an awful lot of stuff online.

 

[redbaron1982]

19 hours ago, EricJ said:

There's an IO-360-P1A manual available on Lycoming's site now, too. 

Is there an actual IO-360-P1A or IO-360-N1A engine or are these just "fake" names to have a generic IO-360 manual? I've just finished printing the N1A, I think I will throw it away and print the P1A that seems to be more complete.