Low Oil Pressure at Idle

[HIghpockets]

Recently noticed at idle the oil pressure drops to yellow arc at idle on fuel pressure gauge. Jumps into the green at takeoff and during flight. Engine is an IO360 A3B6 with about 270 hrs.

Any ideas about the cause?

Thanks.

[neilpilot]

Sounds normal to me

[Guest]

Oil type, temperature and engine RPM all will affect oil pressure.  Oil pressure lower than the green arc at idle power is OK.

Verify the oil pressure with a known mechanical test gauge, before worrying too much.

Clarence

[neilpilot]

18 hours ago, HIghpockets said:

oil pressure drops to yellow arc at idle on fuel pressure gauge

While oil pressure in the yellow at idle sounds normal to me, I’m a bit surprised that you’re able to read oil pressure on the fuel pressure gauge. My older E and C had different oil and fuel pressure gauges.  How are the J gauges arranged?

[PT20J]

[kortopates]

Indeed, like most questions asked here, the answer is in the POH. We had another pilot ask this very same thing just a couple of weeks ago too. I hope pilots get the hint how important it is to familiarize themselves with their respective POH; especially the Limitations section.

[PT20J]

34 minutes ago, kortopates said:

Indeed, like most questions asked here, the answer is in the POH. We had another pilot ask this very same thing just a couple of weeks ago too. I hope pilots get the hint how important it is to familiarize themselves with their respective POH; especially the Limitations section.

A lot of other common questions are readily answered by referring to the Service and Maintenance Manual and Illustrated Parts Catalog. If you are going work on your plane, you really need copies of these, and they are available in pdf format from Mooney. I keep all the manuals for the airplane and avionics on my iPad for ready reference. I also keep them on a thumb drive in the airplane for when I'm "on the road" in case I need to get work done at a shop that doesn't have copies for my model .

Skip

[DonMuncy]

You know we only read the instructions after all else has failed. 

[PT20J]

49 minutes ago, DonMuncy said:

You know we only read the instructions after all else has failed. 

We used to have a tech support guy at a small software company that coded the resolution to a lot of support calls "RTFM". When I asked, he explained it means Read The F***ing Manual. 

[Skates97]

1 hour ago, PT20J said:

We used to have a tech support guy at a small software company that coded the resolution to a lot of support calls "RTFM". When I asked, he explained it means Read The F***ing Manual. 

Our IT guys like to call them "I-D-10-T" errors.

[Oldguy]

2 hours ago, Skates97 said:

Our IT guys like to call them "I-D-10-T" errors.

AKA "PEBCAK" - Problem Exists Between Chair And Keyboard.

[HIghpockets]

Gentlemen,

I appreciate your responses. Indeed, when I was able to recover my POH from my airplane I read the above. (This is a tough room to work).

[Skates97]

46 minutes ago, HIghpockets said:

Gentlemen,

I appreciate your responses. Indeed, when I was able to recover my POH from my airplane I read the above. (This is a tough room to work).

It can be a tough crowd, but worth it to stick around (most of the time...)

[Bob_Belville]

Like the best teachers we had in school, at least before Ms. Smarty Pants Google, some of our MS experts know we'll learn more looking something up than being given the answer.

(A few of you may remember Sydney Harris, a widely read pundit who has probably been dead 30 years. Every so often his column was titled "Things I learned while looking up something else".)

I never know what I might discover while trying to be a little less ignorant in some field...

 

[Guest]

11 hours ago, HIghpockets said:

Gentlemen,

I appreciate your responses. Indeed, when I was able to recover my POH from my airplane I read the above. (This is a tough room to work).

We’re just confirming what you’d read in the PoH earlier.

Clarence

[211º]

I’ve has this happen before. If I understand the concern is. It not so much the reported value of the gauge, it is that the reading has changed from higher values at idling vs. the lower noted idling RPM that you’re now seeing.

Isn’t there a ball in socket pressure relief valve on the back right of the engine.

You might consider having your mechanic or you remove and clean out any debris or sludge in this valve and reinstall. It might not be flush at lower RPMs, but is being set at higher RPM.


Sent from my iPad using Tapatalk Pro

[cliffy]

Also some have noticed that after a hot day flight and using multi grade oil (15-50) that the idle oil pressure drops below the idle min for a few mins as the oil cools. Thin oil to begin with made thinner by heat = lower oil pressure

Cold day flights do not, in most cases, show this anomaly. 

[carusoam]

Notes on oil flow, oil pressure, and oil temperature....

1) The oil pump for the engine is a gear pump... that generates flow....

2) The restriction at the end of the oil gallery is the oil pressure regulator... adjustable spring and ball closing/regulating the flow channel... the restriction generates pressure as the oil flows...

3) The oil viscosity is a measurement of its resistance to flow...

4) Oil’s resistance to flow changes with temperature... selectable by the oil’s  ‘weight’...

5) the gear pump is indirectly connected to the crank... and changes oil flow related to the engine rpm...

6) higher rpm generates more oil flow, that appears on the oilP gauge as more pressure...

7) idle rpm generates less oil flow, that appears on the oilP gauge as less pressure...

8) The yellow range tells the pilot it is OK to run here... just don’t fly in the yellow range...

9) On cold days, we wait for everything to warm into the yellow range... a sign that it is Ok for the next step...

10) On hot days, the viscosity of oil tends to be very watery, extra low viscosity... so the combination of low oil flow, low rpm, and low viscosity, shows up on the gauge as low OilP...

11) As the rpms come up for T/O the OilP should be in the green arc...

 

12) If the The OilP isn’t getting to the green arc with rpms... there are a bunch of things to check...

• Oil type and weight...
• oilT
• If the oilT is high... check the oil cooler for proper operation...
• Also check the vernatherm for proper operation...
• Make sure anything left over for winter ops has been swapped out for summer ops...

13) Setting the oil pressure regulator isn’t a common need.  But it is settable if everything else has been proven out properly...

14) once the oilT has come up, the OilP shouldn’t fall out the bottom of the yellow range... if it does, check with your mechanic...

15) if Cliffy only typed a little quicker, I would have saved a few minutes... 

PP thoughts only, not a mechanic...

Best regards,

-a-

 

 

[cliffy]

Some people only use 2 fingers to type :-)

 

[kortopates]

On 8/23/2019 at 8:54 PM, carusoam said:

Great summary and advice, but some corrections to some misprints and some additional details:

8) The yellow range tells the pilot it is OK to IDLE here... just don’t takeoff or cruise in the yellow range...

9) On cold days, oil pressure at startup may be above green arc, we wait for everything to warm into the green range... a sign that it is Ok for the next step...But see your POH limitations section, as almost every engine specifies a minimum oil temp for runup and takeoff as well as a maximum oil pressure for cold startup. As an example,  for many Continentals these numbers are 75F for the run-up, 100F for takeoff and a maximum green arc pressure of 100 PSI allowing for 110 PSI with a cold engine start. But again, see your POH Limitations section. 

9a) If oil pressure falls off below the green arc in cruise, into the yellow, make a precautionary landing.... You only have minutes not hours... If your flying a turbo seeing oil pressure steadily decline to the bottom of the green arc, you are likely pumping oil overboard. Don't wait for it to fall into the yellow arc.... make a precautionary landing before risking the engine to damage or worse; having to make a dead stick landing.  If successful, your friends might congratulate you on a great dead stick landing, but you'll know this was a pilot induced emergency for failing to notice a loss of oil pressure. (it's happened and no doubt will happen again, but it need not happen to you)

10) On hot days, the viscosity of oil tends to be very watery, extra low viscosity... so the combination of low oil flow, low rpm, and low viscosity, shows up on the gauge as low OilP... knowledge is power and knowing that oil pressure changes inversely proportional to oil Temp will enable you to tell if that redline excursion in oil temp is a gauge indication failure or very real warranting immediate action. But the inverse is not true, low oil pressure does not need high oil temp to be corroborated since a low oil level can also cause low pressure. 

11) As the rpms come up for runup RPM  the OilP should be in the green arc...else abort the intended flight.

12) If the The OilP isn’t getting to the green arc with rpms... there are a bunch of things to check...

• Oil Level; especially on turbo's 
• Oil type and weight...
• oilT
• If the oilT is high... check the oil cooler for proper operation...
• Also check the vernatherm for proper operation...(A faulty vernatherm, that fails to expand and fully seat, no longer directing all oil into the oil cooler, but allowing some to continue to bypass, will results in higher oil temps) 
• Make sure anything left over for winter ops has been swapped out for summer ops...

13) Setting the oil pressure regulator isn’t a common need.  But it is settable if everything else has been proven out properly...

14) once the oilT has come up, the OilP should fall out the redline and into the top of the green range... if it doesn't, check with your mechanic...

.......

 

 

Edited August 26, 2019 by kortopates

[JohnB]

Good comments! Yes that's normal. One of the things I've noticed is that as our monitoring gauge accuracy goes up with the newer digital engine monitoring instruments, we end up discovering and worrying about a lot of things that aren't problems because we can now read them more accurately compared to the analog needles. (I'll admit, I did this for a while for some non problems when I went digital)  But also, if there is a problem, we should be able to pick it up a lot quicker nowadays! 

 

Paws

[81X]

Seems pretty normal for the heat of summer.  For example, on a typical July/August SC day, it's 90+ for most of the day.  After landing and below 1000RPM, my TSIO360 oil pressure is at the bottom of the yellow.  On a rare day like today where it was barely above 70, the post-landing taxi was more in the middle of the yellow arc.  Same oil, filter, etc., but the oil was certainly cooler than a normal day.   

[nels]

On 8/19/2019 at 6:59 PM, HIghpockets said:

Gentlemen,

I appreciate your responses. Indeed, when I was able to recover my POH from my airplane I read the above. (This is a tough room to work).

One of the best bits of advice I got in my life time was from my 5th grade teacher. She said “there is no such thing as a dumb question”.

In regards to engine oil pressure at idle...are your cowl flaps open?

[Yetti]

On 8/19/2019 at 11:41 AM, PT20J said:

A lot of other common questions are readily answered by referring to the Service and Maintenance Manual and Illustrated Parts Catalog. If you are going work on your plane, you really need copies of these, and they are available in pdf format from Mooney. I keep all the manuals for the airplane and avionics on my iPad for ready reference. I also keep them on a thumb drive in the airplane for when I'm "on the road" in case I need to get work done at a shop that doesn't have copies for my model .

Skip

I have the Lycoming Engine Operating Manual, and the Propeller Manual.   I have always wondered if they are REQUIRED to be in the plane....    sure I could look it up in the CFRs, but would I know the answer once I have done that.

[PT20J]

Interesting question. Since neither manual has operating limitations specific to your airplane that are not included in the AFM, you don’t need them in the plane. The reason you need 50 lbs of avionics manuals is that the Limitations section of the AFM supplements frequently require the full manuals to be a available. Any Limitation listed in the AFM is legally binding  

Skip