Oil Pressure

RyanB

RyanB

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What’s considered acceptable? I note that at idle, I’m just under 50psi, which is in the yellow. At cruise power, it’s about 75-80psi, solidly within the green about mid range. Is it acceptable for pressure to fall in the yellow at idle and taxi speeds?

O360A4M on Archer II
 
Lycoming operation manual for O-360 says idle pressure should be 25psi and in-flight a min of 55 and a max of 95psi. So I'd say your fine. My cherokee stayed at 60psi no matter what
 
Hmm, have you looked at Chapt 2 of your POH? If an older plane, look at the POH for a newer model.

Most engines have a minimum oil pressure at Idle that is lower than allowed for cruise.

For my plane, 10 psi is allowed for Idle. 30 psi for cruise. Yellow arc from 10 to 30, green from 30 to 80, redline at 100.
 
RyanB said:
What’s considered acceptable? I note that at idle, I’m just under 50psi, which is in the yellow. At cruise power, it’s about 75-80psi, solidly within the green about mid range. Is it acceptable for pressure to fall in the yellow at idle and taxi speeds?

O360A4M on Archer II
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It's OK, unless this is a recent development. That would indicate something like an internal leak, or something wearing rapidly.

When the oil is hot it's typical for the oil pressure to fall off somewhat at idle. The small Continentals are worse this way; Lycomings have a pump that will pump about four times as much as the engine needs when it's new. The small Continentals have smaller pumps, giving less margin in the supply.
 
RyanB said:
What’s considered acceptable? I note that at idle, I’m just under 50psi, which is in the yellow. At cruise power, it’s about 75-80psi, solidly within the green about mid range. Is it acceptable for pressure to fall in the yellow at idle and taxi speeds?

O360A4M on Archer II
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What type of engine instrument are you using? I have the original gauges for oil pressure, typically on start up it is at the lower end, increases for run up and in flight. Those gauges do not seem super accurate, so know the norms and if something changes then take note of it. I noticed a bit difference in winter flying vs summer flying, oil pressure I believe was lower in hot weather which freaked me out but that’s just because of the weather and now I know how the plane runs. Low oil pressure in flight = get close to an airport or acceptable landing site.
 
The amount of oil pumped is proportional to engine rpm but the restrictions it's being forced through (bearing clearances, etc.) don't change, so the pressure will change with rpm. The pressure also drops as the oil warms and gets thinner. The maximum pressure is limited by the relief valve.
 
RyanB said:
What’s considered acceptable? I note that at idle, I’m just under 50psi, which is in the yellow. At cruise power, it’s about 75-80psi, solidly within the green about mid range. Is it acceptable for pressure to fall in the yellow at idle and taxi speeds?

O360A4M on Archer II
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If you would read the POH for the Archer II you would discover 25 # is the lowest allowable oil pressure.
 
Now that the serious answers are out of the way...

You may have noticed that if you have an oil pressure "gauge" in your car, it ALWAYS goes to the same reading and never changes. Never. I know the guy who did that.

Back in the late '70s Lincoln came out with the Verrysilly that had a Toyko by night digital dashboard that used a bar graph for oil pressure etc. Didn't take long before warranty for oil pressure problems went through the roof. Customers were noticing that the oil pressure was erratic and sometimes went to zero for a moment. It was insane. Dealers were replacing dashboards, engines, whatever... Big BIG Bucks. So, a buddy is in the hot seat. Big time. He gets some samples of warranty returned oil pressure sending units, puts them on a shaker table, and, whaddayaknow when you shake it the mechanical wiper would bounce and you would get intermittent open circuits. Try some new sending units. Same thing. Turns out the sending units have always been doing this, but the old analog gauge just didn't react fast enough for anyone to notice.

OK, we need a quick fix. Something temporary to get the warranty under control while the sending units get redesigned. My buddy has an idea. He gets the vendor to give him some samples of normally open oil pressure switches (production was normally closed), puts a 22? Ohm resistor in series and connects it to a dash board and puts it on the shaker. Perfect. No glitches. Puts it in a car, gives the keys to the boss and says "drive this, tell me what you think". Boss returns "Great you fixed it, what did you do?". Switch and resistor. Boss: "You can't do that! People want a gauge. No way am I going to let you do this."
Buddy: "Warranty is running $xxxxxx per month."
"OK, but just until you come up with a fix for the sender."
Parts go into production and to the dealers...
Warranty goes from insane to best in the industry for oil pressure issues.
Not only that, but customers were writing letters saying how much they like their Verrysilly and how solid the engine seems because the oil pressure never changes, blah blah blah.
Other engine guys start asking questions... "Hey! Can you put those in my engine?"
Management says "You can't do that! People want a gauge."
Engine guys say "Look at the warranty cost."
Management finally caves and says, "OK, but not the Mustang. Mustang owners are enthusiasts. They get a real gauge."
Isn't long before the Mustang guys go crying to management - "Please, Please, Please..."
"OK, but keep the sending unit as a fix for the customers who complain about the fake gauge."
No one complains.

Toyota finds out.

They do a big study and ladle out the Toyota ******** about the harmonious relationship with the car and how much more confident customers feel if the gauge doesn't move, blah blah blah. So, I go to some training about quality stuff and they are telling me about Toyota and the gauge that is not a gauge. Well, duh.

And now, with everything electronic, even the coolant temperature gauge is "tweeked" such that it quickly warms up to the middle doesn't move as the thermostat cycles and won't move until you get seriously hot. So it does move, but there is a big flat spot where it just sits there.

And that's why the gauges in your car do what they do.
 
Good explanation on modern auto oil pressure gauges. They work like an on/off switch. Either you have pressure or you don't ...
 
My car has one of those non-gauges for coolant temp. My wife's car just has a blue light that comes on after a cold start; not sure what that tells me that I didn't already know. Presumably there's also a red idiot light.
 
Not all cars are like that. My BMW M3 oil pressure gauges does move at times. Mainly a good hard track session, oil temp goes up.

Water temp is normalized and does not often move.

OTOH, in the 80s I had a car with a oil pressure gauge, that read a bit low. I thought it was just the sauge, until it turned a rod bearing. Did a complete rebuild with racing spec parts, including oil pump.
Same gauge and sending unit, but all of a sudden, the oil pressure was where it was supposed to be.
 
RyanB said:
What’s considered acceptable? I note that at idle, I’m just under 50psi, which is in the yellow. At cruise power, it’s about 75-80psi, solidly within the green about mid range. Is it acceptable for pressure to fall in the yellow at idle and taxi speeds?
Click to expand...

I had the exact same concern when I started training in Arrows and when I bought mine. It's exactly the same behavior you describe.
High yellow during idle + taxi. Then during run-up it's in the green (after allowing engine to warm). Then during flight it's perfectly centered in the green.
Now that I've put a few hundred hours on it I've come to expect it, since it will reliably do that every time.
It also helps that the other 2 arrows that I originally trained in suffered from the same issue, and both CFIs seemed to brush it off as normal.
Given that you're also experiencing it in your Archer II, I'm inclined to think it's a piper thing... :) I wouldn't worry about it at all.

Now... If it can't achieve normal range during run-up or in cruise, it's landing time :eek:
 
Tom Wells said:
I had the exact same concern when I started training in Arrows and when I bought mine. It's exactly the same behavior you describe.
High yellow during idle + taxi. Then during run-up it's in the green (after allowing engine to warm). Then during flight it's perfectly centered in the green.
Now that I've put a few hundred hours on it I've come to expect it, since it will reliably do that every time.
It also helps that the other 2 arrows that I originally trained in suffered from the same issue, and both CFIs seemed to brush it off as normal.
Given that you're also experiencing it in your Archer II, I'm inclined to think it's a piper thing... :) I wouldn't worry about it at all.

Now... If it can't achieve normal range during run-up or in cruise, it's landing time :eek:
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Its normal and it’s not just “a Piper thing”. Pick any random car engine you want that was built in the last 60-70 years and put a mechanical gauge on it. You’ll see the same fluctuations in oil pressure, hot or cold. It’s a simple function of how an oil pump and oil system works, and one of the reasons the factory oil pressure gauges are numbed, as was already mentioned.
 
I think the minimum allowable oil pressure at idle for a Continental O-300 is 5lbs. I have never seen it that low but that is what the book says.
 
On some models of the Jaguar XJ6 they replaced the accurate oil pressure gauge with one that simply went to a mid-green point on the arc and stayed there at any PSI above 10.

:)
 
same o360 A4a as OP; high 50's during taxi/idle - mid to high 70's in cruise. All normal. I think 'we' notice it more now that most (?) have some sort of digital engine monitor, previously, ignorance was less stressful!
 
Most cars just have idiot lights now anyways.

I'm trying to find the oil pressure gauge on my Tesla. Can anyone help?
 
Rgbeard said:
On some models of the Jaguar XJ6 they replaced the accurate oil pressure gauge with one that simply went to a mid-green point on the arc and stayed there at any PSI above 10.

:)
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Probably the same switch-and-resistor setup Mr. Thorpe described.

People who grew up driving cars with idiot lights are not used to seeing an oil temp gauge fluctuate with RPM and oil temperature, and they get alarmed. Airplane owners who install EI of JPI engine monitors get alarmed at the modest differences in EGT and CHT between cylinders. They were used to, at most, A CHT and an EGT that read off one cylinder. Some airplanes only had an oil temp gauge, no CHT or EGT. Some of us got frustrated when we started flying glass panels, with the digital airspeed readout. We ended up chasing that number, trying to nail book climb speed, for instance. The old needle on the ASI was fine as long as it was close to the mark.

Too much information can cause concern where no concern is warranted. One has to learn what a concerning reading might be. And cross-check that reading with other sources. For instance, if the EGT on a cylinder drops to nothing, but the engine is still running smoothly, does that cylinder really have a problem? If the oil temperature reading suddenly goes up, did you just turn on the landing lights or some other heavy load? A bad engine ground can do that. Turn the lights off and see if the temp goes back to normal.
 
Dan Thomas said:
Airplane owners who install EI of JPI engine monitors get alarmed at the modest differences in EGT and CHT between cylinders.
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I'll bite... what's an example of a modest EGT delta, and what's an example of one where you'd start looking at baffling/induction?
 
GeorgeC said:
I'll bite... what's an example of a modest EGT delta, and what's an example of one where you'd start looking at baffling/induction?
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You'd need to have a point of reference first. Was there always a slight delta? Was the engine running properly at the time of installation so you know that your point of reference is valid?

When we run engines in the test lab we have baseline engines and other methods of auditing data quality to determine if the measurement is reasonable or not. Same applies here, except you'll often just be met with a blank stare when the person reporting a "problem" is asked how it was determined that there is a problem in the first place.
 
GeorgeC said:
I'll bite... what's an example of a modest EGT delta, and what's an example of one where you'd start looking at baffling/induction?
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The pilots guide for my JPI 830 says EGT differences for a fuel injected engine should be in the range of 50 - 90 degrees. Higher for carb.
 
Er, I meant CHT, not EGT :oops:

mondtster said:
You'd need to have a point of reference first. Was there always a slight delta? Was the engine running properly at the time of installation so you know that your point of reference is valid?
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I'll collect some data... and stop hijacking Ryan's thread.
 
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GeorgeC said:
Er, I meant CHT, not EGT :oops:

I'll collect some data... and stop hijacking Ryan's thread.
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If your engine monitor has a recording feature it helps you establish a baseline. When we analyze data for various tests we often look for abrupt steps in the data and if something changed we try to figure out what happened. Sometimes something happened in the test cell and other times something happened to the engine.

Practical limits for CHT have been discussed numerous times. There can be variance between individual cylinder head temps for numerous reasons, such as baffling design, air/fuel mixture distribution, etc. so I’d likely take a recording that you believe is from a known good configuration and compare each cylinder against itself in future runs.
 
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