Fluctuating indication in oil pressure gauge

[PTK]

IO360 A3B6D. Oil pressure gauge was fluctuating today. It was middle of the green as usual for most of the flight except when it started a funny dance. It jerked back and forth from green to pegged high. Did that for several minutes and then it seemed to behave and indicate mid green. It never went below the middle of the green. I cross checked it to the JPI which indicated a solid 81 psi during the gauge dancing. 

Has anyone experienced this? I’m not concerned because it never went below mid green. The excursion was always towards high. Also JPI was solid. Just curious if anyone has witnessed this mysterious oil p gauge dance! If it’s the gauge or ground or something else.

[KSMooniac]

Sounds like an electrical connection issue...I'd start with the grounding jumper behind the panel for the cluster gauge. You might pop the glareshield off, remove the wire terminal, scotch brite the terminal and the panel and then reassemble.

Sent from my LG-US996 using Tapatalk

[carusoam]

Peter,

 

You may want to... Verify if the two gauges are reading from the same sensor...

They probably are.  This means one gauge is telling the truth and the other needs some help...

It is probably either receiving a bad signal or connected to a bad ground.... going with Scott from Kansas’s idea makes a lot of sense...

But,  (looking for alternative ideas to explain why the needle pegs to the high side ...)

What would cause the gauge to peg to the high side...?  

I would expect no input might fall to the low side...

No ground, might also fail to the low side...

Anyone know how the pressure sensor works?  Variable voltage range?  Variable resistance range?  Zero input fails to the high side?

Is there a second pressure sensor, and it is failing?

PP Thinking out loud....

Best regards,

-a-

 

[CaptRJM]

Different motor but I’ve seen the same thing. I have 2 senders, one for ships gauge and a second for the JPI 830.  Ships gauge was dancing from near zero to normal whereas JPI was rock solid at 51 PSI.  I was near home and decided to believe my much newer JPI installation. Turned out that sender for ships gauge was faulty. Swapped it out and it has been fine ever since. 

[PTK]

1 hour ago, carusoam said:

Peter,

 

You may want to... Verify if the two gauges are reading from the same sensor...

They probably are.  This means one gauge is telling the truth and the other needs some help...

It is probably either receiving a bad signal or connected to a bad ground.... going with Scott from Kansas’s idea makes a lot of sense...

But,  (looking for alternative ideas to explain why the needle pegs to the high side ...)

What would cause the gauge to peg to the high side...?  I 

I would expect no input might fall to the low side...

No ground, might also fail to the low side...

Anyone know how the pressure sensor works?  Variable voltage range?  Variable resistance range?  Zero input fails to the high side?

Is there a second pressure sensor, and it is failing?

PP Thinking out loud....

Best regards,

-a-

 

Anthony, I was thinking along the same lines and have to verify sensor question because I honestly don't remember. I'm almost positive though they are on separate sensors. JPI has its own sensor. Which leads me to think it's something isolated to ship sensor or gauge.

[ArtVandelay]

They are not reading from the same sensor, Jpi has it’s own from my experience, and if it’s a ground problem I would expect all gauges to be affected since they share the ground connection.

[PTK]

1 hour ago, CaptRJM said:

Different motor but I’ve seen the same thing. I have 2 senders, one for ships gauge and a second for the JPI 830.  Ships gauge was dancing from near zero to normal whereas JPI was rock solid at 51 PSI.  I was near home and decided to believe my much newer JPI installation. Turned out that sender for ships gauge was faulty. Swapped it out and it has been fine ever since. 

Thank you Capt. It never went below mid green. That's what's throwing me off.

[chrisk]

I had this problem on my 231. --The engine could be off and the pressure would be in the green arc, but only sometimes.  And in flight, it would start off normal, and then it would go pegged high, and then eventually return to normal.   It was impossible to trust the gauge.   It turned out to be the ground. Basically, the pressure sensor is a cylinder at the end of a tube.  One lead on the sensor goes to the gauge.  The clamp surrounding the sensor is the only ground connection.  I had the mechanic clean the sensor and re-tighten the band around the pressure sensor.  Its been perfect since then.  --Maybe yours is similar.  Let us know.

[carusoam]

Interesting second pice of evidence that a ungrounded or improperly/dirty ground to the sensor can cause the gauge to fail high! 

Matching Peter’s original description...

Nice added detail Chris!

Best rgeards,

-a-

[chrisk]

6 hours ago, carusoam said:

No ground, might also fail to the low side...

 

-a-

 

On the 231, no ground will fail to the high side.   I personally verified this.

[carusoam]

@PTK heads-up for Peter...

Looks like MS has some good ideas for your OilP sensor...

Hope you get this note in a timely manner.  

Best regards,

-a-

[JohnB]

12 hours ago, PTK said:

IO360 A3B6D. Oil pressure gauge was fluctuating today. It was middle of the green as usual for most of the flight except when it started a funny dance. It jerked back and forth from green to pegged high. Did that for several minutes and then it seemed to behave and indicate mid green. It never went below the middle of the green. I cross checked it to the JPI which indicated a solid 81 psi during the gauge dancing. 

Has anyone experienced this? I’m not concerned because it never went below mid green. The excursion was always towards high. Also JPI was solid. Just curious if anyone has witnessed this mysterious oil p gauge dance! If it’s the gauge or ground or something else.

Wow.  It is amazing how we can share the same experiences. I had the exact same thing for my oil temperature gauge. It danced then pegged full hot. All of my other gauges including my oil pressure gauge and JPI were normal. We first replaced the probe. And it didn't fix the problem. Then LASAR was amazingly able to fix the oil temp gauge mostly since replacement for these gauges aren't available from mooney, and it worked most of the time after that. By the way, if your mechanic says you need a replacement oil pressure gauge, and Mooney doesn't make them, ive got one if you're interested, you would have to check if it would work on your J though.

[PTK]

5 hours ago, chrisk said:

I had this problem on my 231. --The engine could be off and the pressure would be in the green arc, but only sometimes.  And in flight, it would start off normal, and then it would go pegged high, and then eventually return to normal.   It was impossible to trust the gauge.   It turned out to be the ground. Basically, the pressure sensor is a cylinder at the end of a tube.  One lead on the sensor goes to the gauge.  The clamp surrounding the sensor is the only ground connection.  I had the mechanic clean the sensor and re-tighten the band around the pressure sensor.  Its been perfect since then.  --Maybe yours is similar.  Let us know.

Thank you Chrisk.This is exactly what I needed to verify that ungrounded or intermitent ground will fail gauge to high. Any idea where ship’s oil p sensor is located? I might clean it and retighten it myself if it’s easily accesible from top without removing bottom cowl.

 

[Guest]

1 hour ago, PTK said:

Thank you Chrisk.This is exactly what I needed to verify that ungrounded or intermitent ground will fail gauge to high. Any idea where ship’s oil p sensor is located? I might clean it and retighten it myself if it’s easily accesible from top without removing bottom cowl.

 

It is usually mounted on the engine mount structure with clamps on the right rear side of the engine near the oil filler tube.

Removing the top cowl should be all that you need to do.

Clarence

Edited April 22, 2018 by M20Doc

[M016576]

1 hour ago, PTK said:

Thank you Chrisk.This is exactly what I needed to verify that ungrounded or intermitent ground will fail gauge to high. Any idea where ship’s oil p sensor is located? I might clean it and retighten it myself if it’s easily accesible from top without removing bottom cowl.

 

I had the same issue with my previous J. My oil pressure ships gauge started to “windshield wiper” between full off the right side of the gauge and it’s usual reading in the green arc.  It turned out that it was also a dirty ground, as Chris stated. 

Two places to look: at the terminals on the gauge cluster, and at the grounding post.  The terminals are directly under the glare shield- just remove it, you’ll see the post on the back of the gauge.  It has a nut on it holding the ground wire.  In the case of my current.. and previous J, they both ground to the stack that’s just to the left of the roll cage bar that runs down the middle of the cockpit (ie- holds the wet compass).  

On my previous J, the ground at the back of the gauge was dirty.  I took the nut off, filed the contact on the ground wire, then sprayed it with contact cleaner.  The gauge worked fine from there on out.  It took about 25 minutes total, all in.

the actual pressure sender is on the oil cooler on my current J (but it has an IO-550... missile STC).  Can’t remember where the sender is on the IO-360.  Honestly- I’d start with the gauge ground first- then, if that doesn’t work, check the integrity of the wiring to the sender.

 

Edited April 22, 2018 by M016576

[M016576]

6 hours ago, chrisk said:

I had this problem on my 231. --The engine could be off and the pressure would be in the green arc, but only sometimes.  And in flight, it would start off normal, and then it would go pegged high, and then eventually return to normal.   It was impossible to trust the gauge.   It turned out to be the ground. Basically, the pressure sensor is a cylinder at the end of a tube.  One lead on the sensor goes to the gauge.  The clamp surrounding the sensor is the only ground connection.  I had the mechanic clean the sensor and re-tighten the band around the pressure sensor.  Its been perfect since then.  --Maybe yours is similar.  Let us know.

That’s exactly what I saw on my J with a dirty contact on the back of the gauge cluster.

my gauge was intermittently going from full pegged to the right back to the normal reading.  Clearly to me it wasn’t reading right... the movements were too erratic. 

Edited April 22, 2018 by M016576

[PTK]

Went to airport today to visit the dancing oil pressure indication. I addressed the obvious which was the nut holding connector under the protective cap. It was loose enough to turn by hand and had a little oil on it which probably dripped on it from last oil change. Cleaned it good and tightened it. The band around the sensor (ground) was tight. We’ll see tomorrow when I'll fly it.

My question is will that connector being intermittent also fail the gauge to peg high? Similar to the ground band around the sensor as has been suggested? 

[chrisk]

I would think you found the problem.  Fly it and see.