Oil pressure adjustment

[rotorman]

I have put about 30 hrs on my rebuilt IO 360 A3B6. From the start the warm oil pressure was high. In the yellow range which on the gauge is pretty narrow.  Last flight it was touching the red range. I decided to turn it down. I turned the adjuster out (tension off the spring) 3 turns. I ground ran it with warm (not hot) oil up to about 2000 rpm. The pressure seemed to come down some but I will not know for sure until I fly it again. What effect should I expect from 3 full turns? I wanted to lower from 100 psi to 90.

[Guest]

There is no linear value when adjusting the oil pressure.  I would confirm the numbers your seeing with a known test gauge before making changes.

Clarence

[EricJ]

+1 on making sure the pressure is what you think it is with a known gauge first.   Usually the first thing to suspect is the gauge or pressure transducer, which is also the easiest thing to change.

IO-360s run kinda high on pressure.   Mine will occassionally trigger the high pressure alarm on the JPI during takeoff, even on a warm day after warm-up and a long taxi.   I've also had it alarm on a go-around/missed approach after a long descent let the oil cool a bit.    It's a fairly normal thing for me.   I'd think on an engine breaking in it might stay high for a bit until things get worn in and clearances settle a bit.

 

[Guest]

I believe that some time ago Lycoming raised the red line on many engines to 115 PSI. Most airframe manufacturers didn’t follow Lycoming’s change.

Clarence

[A64Pilot]

5 hours ago, rotorman said:

I have put about 30 hrs on my rebuilt IO 360 A3B6. From the start the warm oil pressure was high. In the yellow range which on the gauge is pretty narrow.  Last flight it was touching the red range. I decided to turn it down. I turned the adjuster out (tension off the spring) 3 turns. I ground ran it with warm (not hot) oil up to about 2000 rpm. The pressure seemed to come down some but I will not know for sure until I fly it again. What effect should I expect from 3 full turns? I wanted to lower from 100 psi to 90.

The relief valve doesn’t care about oil temp etc. It will open when the pressure on the valve overcomes the spring, and once it begins to crack open within reasonable limits it will hold that pressure. Of course colder oil being higher viscosity will hit higher pressures at lower RPM than hot thin oil will, so really testing with cooler oil is good.

‘However as has been stated please don’t adjust the oil pressure to make an old never been calibrated gauge read good, until after you have confirmed it’s accurate, a great many aren’t, they were really never precision instruments to begin with, their greatest use was to spot trends, I.E. my gauge usually runs a x, now it’s lower.

Be glad you have an adjustable pressure regulator, many have to be removed and disassembled and washers added or removed. When I overhauled my 540 I installed an adjustable regulator and if memory is right, they aren’t inexpensive.

[rotorman]

21 hours ago, M20Doc said:

There is no linear value when adjusting the oil pressure.  I would confirm the numbers your seeing with a known test gauge before making changes.

Clarence

I don't the suspect the accuracy of the gauge because the old 2,000 hr plus engine ran with the gauge about centered. It only went high after the rebuilt engine was installed. 

Where is a good place to tap into the oil system with a direct reading gauge?

[1964-M20E]

One is to install a temporary Tee in the line that goes to the pressure gauge.  Another method would be to set up a test rig with one of those hand pumps and a separate gauge pump it up to a know value 50, 60 psi and verify the gauge inside it reading the same.  I would choose 3 or 4 different pressures to verify the gauge reads accurately over the entire range.  You would disconnect oil pressure line form the engine and connect the pump to the line.

[Guest]

3 hours ago, rotorman said:

I don't the suspect the accuracy of the gauge because the old 2,000 hr plus engine ran with the gauge about centered. It only went high after the rebuilt engine was installed. 

Where is a good place to tap into the oil system with a direct reading gauge?

Install a Tee in the line to the pressure transducer, then connect a test gauge to the Tee.

Clarence

[A64Pilot]

To simply verify the stock gauge which you do need to fly to do, simply remove the xducer and connect where it was, no T Involved.

‘Do not fly with another gauge installed unless of course its STC’d as a primary.

But the best answer is have a shop with a dead weight tester verify the gauge, that’s the hand pump. what makes it valid is it’s gauge is calibrated

[rotorman]

I took 3 turns off the spring tension on the regulator and the oil pressure came down from 100 to about 87 psi. So it appears on turn is about 5 psi assuming it is linear. The gauge has been consistent through approximately 1500 hours of my ownership with the previous engine. It only went high after the rebuilt engine was installed. I'm pretty confident that the gauge is as accurate as need be.

As an aside, the adjuster on the regulator was not safe tied. The castellated nut on the adjuster is held captive by a pin. The force to move the adjuster is fairly light. It can't be turned by hand but it take little force to turn it. Are these normally safe tied?

[N201MKTurbo]

3 hours ago, rotorman said:

I took 3 turns off the spring tension on the regulator and the oil pressure came down from 100 to about 87 psi. So it appears on turn is about 5 psi assuming it is linear. The gauge has been consistent through approximately 1500 hours of my ownership with the previous engine. It only went high after the rebuilt engine was installed. I'm pretty confident that the gauge is as accurate as need be.

As an aside, the adjuster on the regulator was not safe tied. The castellated nut on the adjuster is held captive by a pin. The force to move the adjuster is fairly light. It can't be turned by hand but it take little force to turn it. Are these normally safe tied?

I’ve never seen one lock wired. The rubber seal on the screw does a good job of holding them in place. I think if the screw backed all the way out, you would still have enough pressure to keep the engine going. It takes about 30 PSI to open the piston nozzles. Don’t quote me on that, I’d have to look it up. 

[A64Pilot]

One on my IO-540 was not saftied, I think the adjustable ones are uncommon. The non adjustable ones have to be removed and taken apart and washers either added or removed.

[EricJ]

4 hours ago, rotorman said:

I took 3 turns off the spring tension on the regulator and the oil pressure came down from 100 to about 87 psi. So it appears on turn is about 5 psi assuming it is linear. The gauge has been consistent through approximately 1500 hours of my ownership with the previous engine. It only went high after the rebuilt engine was installed. I'm pretty confident that the gauge is as accurate as need be.

Was it rebuilt at an engine shop and test run?   The engine test stands are required to use calibrated gauges, so it'd be unlikely to be delivered with the pressure set improperly.   Another possibility is that your gauge reads low and has for some time.   Definitely worth checking against a known reference gauge.

[rotorman]

The engine is a rebuild from Western Sky. And it was run. Thanks for reminding me because I have the run numbers. It does appear that my gauge is reading about 10 psi high. The consensus was to check the gauge is sound advice.

[carusoam]

Great details in a follow-up rotorman!

Thanks for the post.

Best regards,

-a-