Oil pressure Question

Keith Douglass

Keith Douglass

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KeithD
So I was doing my third solo flight today. My home base is KDVT and I go to westwind. I was flying a Cessna 172 SP model. I did the preflight and checked the oil and I was sitting at 7 quarts. I checked under the airplane before and after the flight and saw no dripping or any type of leaks. But when I did the run up and the takeoff, all my instruments were green. after takeoff i was heading to the west when my oil pressure was reading lower than i recall. I pulled the throttle back to about 1500 RPM and it was just at the bottom of the green. At Idle it was out of the green, So i decided to head back. My question is was i just over reacting and its normal with some aircraft, or was there an actual issue. Any responses will be great!
 
Oil pressure is almost always lowest when warm and at low engine speed.

The green arc is above 50 PSI, and is for NORMAL operation. Idle is not normal operation. The lower red arc is at 20 PSI. Getting below that is when you land as soon as practicable.

Yes, you overreacted. The limitation listed in the POH is 20 PSI, corresponding to the red line.
 
You may have over reacted,not being familiar with that particular airplane.
 
I don't think you over reacted at all.

Let's see..... You're not sure about having enough oil pressure.

When you think of the consequences, deciding to be safe and head back is always the right decision.

Sure beats reading the NTSB report from your hospital bed:
"Pilot noticed inadequate oil pressure but decided to keep flying anyway."
 
Non Compos Mentis said:
Let's see..... You're not sure about having enough oil pressure.
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Post-solo, he should be familiar with the POH, especially the difference between green arcs (and their ends) and red lines.

You can indeed be too careful. Putting this aircraft down in a field and then flipping it because he doesn't yet know how to do a good soft field landing would have been an example. Fortunately, it didn't go that far.

Heading back is not always the right thing to do if the oil pressure really is low, especially if accompanied by high oil temperatures. Land at the NEAREST reasonable airport, or at least keep good emergency landing spots well within gliding range at all times. Proceeding across a large lake or forest or mountain range to go home is not a good idea.

So, it's a learning experience. No harm was done, nothing bent, nothing hurt. But it was indeed an overreaction. And a useful one. Part of being a student is learning what's important and what isn't.
 
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The presence of doubt in your mind was sufficient reason to abort the flight and return -- it's a lot better to be down here wishing you were up there than up there wishing you were down here. However, if the oil pressure was in the green, oil temp was normal, and the oil pressure stayed in the green at all normal operating speeds, you would almost certainly have been safe to continue the flight. Talk this over with your instructor, and try to get one of the mechanics to talk with you about what to expect from your engine.
 
By the time the student is ready for solo, shouldn't the CFI have trained the student what an exceptable engine reading are ?
 
7 quarts is perfect for a Lycoming. Most stabilize at 6.5-7. If you fill it to 8 it will just go through it in a couple hours. My Super Cub will sit at 6.5 for 25-30 hours. Fill it to 8 and it goes down to 6.5 in about 3 hours. Also if the oil pressure is in the green it is good. Don
 
Thanks for all the replies and I did fail to mention that all the other aircraft i flew at westwind had much higher oil pressures. This was a new aircraft they purchased about three days ago and barley anyone had any time in it. The oil pressure being a bit lower than the other aircraft was apparently normal according to the mechanics. Yea now that i am thinking about it more i did overreact, I looked more into the POH to confirm everything. Only reason I was worried a bit more about it was because it is getting to the tripple digets here in Arizona and the heat really does a number on the engines. We aren't even allowed to fly if it is above 106 degree's. I will take this as a learning experience and move onto completing my training.
 
Ron Levy said:
The presence of doubt in your mind was sufficient reason to abort the flight and return -- it's a lot better to be down here wishing you were up there than up there wishing you were down here. However, if the oil pressure was in the green, oil temp was normal, and the oil pressure stayed in the green at all normal operating speeds, you would almost certainly have been safe to continue the flight. Talk this over with your instructor, and try to get one of the mechanics to talk with you about what to expect from your engine.
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+1 :yes:

Flying is a learning experience every flight. If your gut tells you something isn't quite right go with your gut and head back to the airport to sort it out.

OP made a good call. :yes:
 
Tom-D said:
By the time the student is ready for solo, shouldn't the CFI have trained the student what an exceptable engine reading are ?
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Of course, but when you are solo you now have to interpret the readings yourself without the instructor.

The student pilot had concerns about his oil pressure. As a mechanic would you rather see him continue to fly? :dunno:
 
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Ron Levy said:
The presence of doubt in your mind was sufficient reason to abort the flight and return -- it's a lot better to be down here wishing you were up there than up there wishing you were down here. However, if the oil pressure was in the green, oil temp was normal, and the oil pressure stayed in the green at all normal operating speeds, you would almost certainly have been safe to continue the flight. Talk this over with your instructor, and try to get one of the mechanics to talk with you about what to expect from your engine.
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This.
 
Keith Douglass said:
Thanks for all the replies and I did fail to mention that all the other aircraft i flew at westwind had much higher oil pressures. This was a new aircraft they purchased about three days ago and barley anyone had any time in it. The oil pressure being a bit lower than the other aircraft was apparently normal according to the mechanics. Yea now that i am thinking about it more i did overreact, I looked more into the POH to confirm everything. Only reason I was worried a bit more about it was because it is getting to the tripple digets here in Arizona and the heat really does a number on the engines. We aren't even allowed to fly if it is above 106 degree's. I will take this as a learning experience and move onto completing my training.
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First, better in this case to overreact by aborting when you didn't need to rather than underreacting by continuing and having something bad happen. Second, I'm a bit surprised they'd let a Student take a plane none of the instructors had taken on a "shakedown" flight to identify any quirks. Third, super-high ambient temps can result in thinning the oil a bit, with accompanying lower oil pressure, but that should not happen without also seeing an extraordinarily high oil temperature -- and with a combination of high oil temp and low oil pressure, you'd be wanting to do something to get them back in the normal ranges promptly or else terminate the flight as soon as practicable.

So, I'm still convinced you did the right thing under the circumstances.
 
Keith Douglass said:
Thanks for all the replies and I did fail to mention that all the other aircraft i flew at westwind had much higher oil pressures. This was a new aircraft they purchased about three days ago and barley anyone had any time in it. The oil pressure being a bit lower than the other aircraft was apparently normal according to the mechanics. Yea now that i am thinking about it more i did overreact, I looked more into the POH to confirm everything. Only reason I was worried a bit more about it was because it is getting to the tripple digets here in Arizona and the heat really does a number on the engines. We aren't even allowed to fly if it is above 106 degree's. I will take this as a learning experience and move onto completing my training.
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If you have doubts, that's reason enough to head down. Most likely though, this is the first really hot day you have flown and this is a normal condition at the high temp.
 
I once had an oil pressure gauge line fail in flight. It dumped all but one quart of the oil overboard. If had been checking the oil pressure more regularly I would have caught it sooner. Sometimes a line can leak, lowering the pressure indication without dropping it right to zero, but the end result is the same.

Many old airplanes used a 1/8" copper line (and some had 1/4") to the engine for the gauge. That was stupid, as copper work-hardens under vibration and will eventually fail if it's left long enough. I have seen it twice now. If I bought such an airplane I would be changing that line to a decent hose assembly.

Electric gauges are notorious for wrong indications. A bad engine ground path can make the gauge read high, and a poor connection at the sender or gauge can make it read low. It only takes fractions of an ohm in the ground path to make it read high.

Dan
 
Ron Levy said:
First, better in this case to overreact by aborting when you didn't need to rather than underreacting by continuing and having something bad happen. Second, I'm a bit surprised they'd let a Student take a plane none of the instructors had taken on a "shakedown" flight to identify any quirks. Third, super-high ambient temps can result in thinning the oil a bit, with accompanying lower oil pressure, but that should not happen without also seeing an extraordinarily high oil temperature -- and with a combination of high oil temp and low oil pressure, you'd be wanting to do something to get them back in the normal ranges promptly or else terminate the flight as soon as practicable.

So, I'm still convinced you did the right thing under the circumstances.
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Under the circumstances so do I, but how did you determine the other CFI's had not flown it on cooler days?
 
Dan Thomas said:
Electric gauges are notorious for wrong indications. A bad engine ground path can make the gauge read high, and a poor connection at the sender or gauge can make it read low. It only takes fractions of an ohm in the ground path to make it read high.

Dan
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Thanks for mentioning this, Dan. My first move (while on the ground) would be to check the gauge calibration. -Skip
 
What sort of oil are you running? Back when I ran straight weights and 40 in the winter, I would see low pressures when the weather warmed up. Not exactly a good thing, but explainable.
 
Tom-D said:
By the time the student is ready for solo, shouldn't the CFI have trained the student what an exceptable engine reading are ?
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I would say he should have been trained in what "normal" readings are, as well as what is absolutely a no-go reading. There are enough variations in between, some of which are acceptable, some of which are not, and some that may or may not be acceptable depending on other factors (trends, for instance), that he can't be expected to know all of the permutations prior to solo.

As you indicated, he did the right thing...he landed safely and further investigated the issue to determine what was acceptable. That's an important skill that will serve him well for years to come.:yes:
 
Pretty sure my oil pressure stays in the green arc at idle even when hot so yeah that would have made me think twice.

You're doing the right thing by asking about what's normal, but you need not second-guess your decision. You're the PIC.
 
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