Oil pressure too high
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Oil pressure too high
I have seen high oil pressure on my last flight. It was near 90 psi all the time (Cessna 172S). Before it was rather in 50-70 psi region.
The oil is AeroShell 15W50, changed in October and flown about 15 hours since.
I was told the lubrication system could be blocked on some place. That would be bad.
Any ideas?
The oil is AeroShell 15W50, changed in October and flown about 15 hours since.
I was told the lubrication system could be blocked on some place. That would be bad.
Any ideas?
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The 360 oil system is really quite simple. An engine driven oil pump circulates lubricant through a series of galleries and oil ways/ports. The oil finds its way back to the sump via gravity and the pump lifts it and pressurises it again.
To prevent too high a pressure, a pressure release valve (prv) is fitted. The prv is sited on the rear of the right hand crankcase above and behind no 3 cyl. It comprises a stainless steel ballbearing and a spring. The ball is forced by the spring against an oil port. When the oil pressure is sufficiently high the ball if forced off its seat and oil is allowed to bypass this restriction thus making sure that the pressure never gets too high.
My first suspicion would be that either the prv has been adjusted to improve pressure or something is preventing the ball from becoming unseated. It's usually a yellow coloured housing with from memory a 7/8" hex as part of the casting. It should also be wire-locked. Not sure how much maintenance you are allowed to do in yr country but your engineer will be able to inspect it in a a few minutes.
Too high an oil pressure is just as bad as too low an oil pressure. 90 is at the top end of the Lycoming scale.
Hope that helps.
To prevent too high a pressure, a pressure release valve (prv) is fitted. The prv is sited on the rear of the right hand crankcase above and behind no 3 cyl. It comprises a stainless steel ballbearing and a spring. The ball is forced by the spring against an oil port. When the oil pressure is sufficiently high the ball if forced off its seat and oil is allowed to bypass this restriction thus making sure that the pressure never gets too high.
My first suspicion would be that either the prv has been adjusted to improve pressure or something is preventing the ball from becoming unseated. It's usually a yellow coloured housing with from memory a 7/8" hex as part of the casting. It should also be wire-locked. Not sure how much maintenance you are allowed to do in yr country but your engineer will be able to inspect it in a a few minutes.
Too high an oil pressure is just as bad as too low an oil pressure. 90 is at the top end of the Lycoming scale.
Hope that helps.
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It would be very unusual for a Mechanical problem to result in high oil px when the engine is hot, the oil you are using is top quality and has a very stable viscocity at high temps but is unlikely to be the cause of the high px indication.
I think that you should look at the indication system, if it is one of the electricly driven gauges it is likely to be the problem.
As stiknruda says you can adjust the PRV but this should only be done if you have a calibrated gauge rigged into the oil system DO NOT trust the cockpit indications as they may be the problem.
I think that you should look at the indication system, if it is one of the electricly driven gauges it is likely to be the problem.
As stiknruda says you can adjust the PRV but this should only be done if you have a calibrated gauge rigged into the oil system DO NOT trust the cockpit indications as they may be the problem.
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stiknruda
For me it looks like the release valve is working as it should, that's the reason why the pressure stays at 90 psi for every rpm.
If the passage of oil is partially blocked, the pump is pressing the oil through smaller throughput causing higher pressure. This forces the oil through the release valve.
My concern is that part of the engine could not be lubricated...
Is there a way how to look after this?
My first suspicion would be that either the prv has been adjusted to improve pressure or something is preventing the ball from becoming unseated.
If the passage of oil is partially blocked, the pump is pressing the oil through smaller throughput causing higher pressure. This forces the oil through the release valve.
My concern is that part of the engine could not be lubricated...
Is there a way how to look after this?
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I agree regarding the indicators being possibly duff.
I had this issue for a year or two after I got my plane from new. The oil pressure indicator uses a transducer which has a vent hole and it gets moisture in there which corrodes the resistor bridge.
Socata released an SB for it, which mistakenly asks for the connector to be sleeved, so they never sussed that there is a hole in the side of the connector base
Incidentally, what exactly is the problem if the oil pressure is too high? Could it crack the crankcase if it was say 1.5x too high? That would suprise me. What could happen is that an "excessive" oil pressure could cause more engine heat to be absorbed by the oil, which would reduce the CHTs but would need a bigger oil cooler to maintain the oil temp to a reasonable level.
I had this issue for a year or two after I got my plane from new. The oil pressure indicator uses a transducer which has a vent hole and it gets moisture in there which corrodes the resistor bridge.
Socata released an SB for it, which mistakenly asks for the connector to be sleeved, so they never sussed that there is a hole in the side of the connector base
Incidentally, what exactly is the problem if the oil pressure is too high? Could it crack the crankcase if it was say 1.5x too high? That would suprise me. What could happen is that an "excessive" oil pressure could cause more engine heat to be absorbed by the oil, which would reduce the CHTs but would need a bigger oil cooler to maintain the oil temp to a reasonable level.
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Incidentally, what exactly is the problem if the oil pressure is too high? Could it crack the crankcase if it was say 1.5x too high?
The indicator can be the the problem. Need to check this. I flew ca. 4 hours with the high indication. If the engine would not be properly lubricated...
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Too high a pressure: as Miroc points out, the oil cooler would be susceptible to damage/bursting but there is a phenomena were the main journals can suffer from a form of cavitation if the oil pressure is too high, this ruins the bearing shells.
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Interesting...
The hoses should be OK because all hoses in common use are 1500psi working pressure. Most people use Teflon hoses nowadays which have a practically unlimited life, too.
The oil cooler I can well believe...
But cavitation of the bearings? Are you sure this is not caused by bits of the camshaft carried by the oil?
The hoses should be OK because all hoses in common use are 1500psi working pressure. Most people use Teflon hoses nowadays which have a practically unlimited life, too.
The oil cooler I can well believe...
But cavitation of the bearings? Are you sure this is not caused by bits of the camshaft carried by the oil?
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High oil pressure will cause oil not to be contained at the weakest point in the lubrication system.
That could be a seal, a gasket, the oil cooler, a sensor or anywhere else.
A simple analogy:
Fill a bicycle pump with water, put your finger over the end and push the plunger. Without too much effort the pressure created will overcome your finger's ability to contain it and presto: a leak!
Now consider the same pump with several different holes in it and several different people with their fingers covering the holes. Whoever allows the fluid out first is the weakest!
If the sensor is an electronic one, a simple test is to power up the instruments without starting the engine. If your oil pressure goes up you have an instrument/sensor problem. If it only goes up once you start the engine then you probably have a stuck PRV .
That could be a seal, a gasket, the oil cooler, a sensor or anywhere else.
A simple analogy:
Fill a bicycle pump with water, put your finger over the end and push the plunger. Without too much effort the pressure created will overcome your finger's ability to contain it and presto: a leak!
Now consider the same pump with several different holes in it and several different people with their fingers covering the holes. Whoever allows the fluid out first is the weakest!
If the sensor is an electronic one, a simple test is to power up the instruments without starting the engine. If your oil pressure goes up you have an instrument/sensor problem. If it only goes up once you start the engine then you probably have a stuck PRV .
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Just out of curiosity. Is the Pressure Relief Valve a safety valve, only to be activated in case of a too-high oil pressure, to protect other components from rupturing/breaking? Or is it a regulator valve to keep the oil at a certain pressure during normal operations?
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BP - it's a safety valve - it only operates when oil at acertain pressure dislodges the ball from its seat. The spring that holds the ball in place can be tensioned by screwing the adjuster in and out - in (clockwise) to increase the tension and "jam" the ball harder against its seat.
If it is a Westach guage, the output voltage from the transducer of 0.5V should give 0 psi. And 4.5v gives full scale deflection.
So by disconnecting the transducer from the electrical plug and putting 0.5v to the output the needle should lift off the stop and read 0psi. Up the voltahge to 4.5 and the needle should read fsd.
You'll now know if your guage functions.You can test the transducer in a similar way with amultimeter and an airline.
Don't ask how I know this!!
Allegedly oil cavitation on bearing shells leaves strange witness marks on the bearing face - a bit like corrugations.
If it is a Westach guage, the output voltage from the transducer of 0.5V should give 0 psi. And 4.5v gives full scale deflection.
So by disconnecting the transducer from the electrical plug and putting 0.5v to the output the needle should lift off the stop and read 0psi. Up the voltahge to 4.5 and the needle should read fsd.
You'll now know if your guage functions.You can test the transducer in a similar way with amultimeter and an airline.
Don't ask how I know this!!
Allegedly oil cavitation on bearing shells leaves strange witness marks on the bearing face - a bit like corrugations.
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BP - it's a safety valve - it only operates when oil at acertain pressure dislodges the ball from its seat.
You said "either the prv has been adjusted to improve pressure" but I can't place that, unless you suggest that the prv previously had been set to open at 50-70 psi (which is apparently well within the green arc) and has now been reset to the 90 psi setting (which is apparently at the top of the green arc).
But that would suggest that it's a regulator valve, not a safety valve.
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I'm not sure its a pressure relief valve. I think it regulates the pressure in normal operation.
I saw an engine that had come back from overhaul where the ball valve had been jammed. The oil cooler had bulged out massively and then failed, so normal operation of the engine had taken the oil pressure way high. This would indicate that the ball valve works as a regulator.
I would be very suspicious of the gauge. I had one suddenly change on me once for no reason. It was a Westach. These require the readout to be adjusted for the particular oil pressure sender unit. This has to be done at the factory I was told, so you can't just change the sender or gauge as they come as a matched pair.
You didn't say which gauge it is.
I saw an engine that had come back from overhaul where the ball valve had been jammed. The oil cooler had bulged out massively and then failed, so normal operation of the engine had taken the oil pressure way high. This would indicate that the ball valve works as a regulator.
I would be very suspicious of the gauge. I had one suddenly change on me once for no reason. It was a Westach. These require the readout to be adjusted for the particular oil pressure sender unit. This has to be done at the factory I was told, so you can't just change the sender or gauge as they come as a matched pair.
You didn't say which gauge it is.
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A PRV's sole function is to prevent over-pressurisation.
The engine itself, that is its' tolerances, clearances and wear, is the regulator which is why a worn engine will give lower oil pressure for a given oil viscosity.
The engine itself, that is its' tolerances, clearances and wear, is the regulator which is why a worn engine will give lower oil pressure for a given oil viscosity.
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I think there is some ambiguous terminology here.
The Lyco engine has a gear pump for the oil. This means the volume flow rate is proportional to the RPM.
This is no good for lubing the engine, which needs a relatively constant supply of oil over the operating rev range, and a constant volume feed would just give you a massively high oil pressure at anywhere near operating revs.
So one has the pressure regulator valve which is a spring loaded thingy which controls the pressure at that point in the oil system.
At any RPM significantly above idle, this valve is partially open and is regulating the pressure.
The actual oil pressure varies around the engine and will be according to how knackered the engine is. A worn out engine will offer less resistance to oil flow (through the various bearing surfaces).
Also, the point where the pressure gauge is fed from varies according to the engine.
The Lyco engine has a gear pump for the oil. This means the volume flow rate is proportional to the RPM.
This is no good for lubing the engine, which needs a relatively constant supply of oil over the operating rev range, and a constant volume feed would just give you a massively high oil pressure at anywhere near operating revs.
So one has the pressure regulator valve which is a spring loaded thingy which controls the pressure at that point in the oil system.
At any RPM significantly above idle, this valve is partially open and is regulating the pressure.
The actual oil pressure varies around the engine and will be according to how knackered the engine is. A worn out engine will offer less resistance to oil flow (through the various bearing surfaces).
Also, the point where the pressure gauge is fed from varies according to the engine.
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IO's got it. The valve is a pressure regulator, not a safety valve.
If the valve has been messed about with (typically screwed down to camoflage engine wear!!!) You can usually spot this with a cold engine. The oil pressure will be roughly proportional to the engine speed - until you reach a point at which the valve lifts.
I've been through this process with a friend's aircraft - where after a fair bit of work being carried out the oil pressure was very high. In that case even when hot the oil pressure was proportional to engine speed. A couple fo minutes with the manual showed that the engine had aquired a number of spacers below the cap......
If the valve has been messed about with (typically screwed down to camoflage engine wear!!!) You can usually spot this with a cold engine. The oil pressure will be roughly proportional to the engine speed - until you reach a point at which the valve lifts.
I've been through this process with a friend's aircraft - where after a fair bit of work being carried out the oil pressure was very high. In that case even when hot the oil pressure was proportional to engine speed. A couple fo minutes with the manual showed that the engine had aquired a number of spacers below the cap......
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The PRV is not a regulator, it is a pressure limiting device in this particular case. The engine does not need to strictly regulate the pressure.
The oil pump must have enough capacity to press the oil through the pipes at idle RPM to lubricate all the places. That's the low limit.
At high RPM the pumped volume will cause pressure to be still below the top of green arc, if the oil has normal viscosity. That means at RPM on top of green the pressure will be in green (always was in my engine). If the oil is cold, the resistance in pipes is high, pressure would rise to the top of green arc and that's the point where the limiting device the PRV will kick in and cut of the excess volume to keep the pressure at the set value. Until this moment it is completely closed. Technically it is a D-type regulator (D=derivating, other types are P=proportional and I=integrating).
If during the normal operation let's say 2350 RPM and warm engine the oil pressure was at ca. 60 psi before and now it is 90 psi, that is a signal something is wrong. It can be the gauge. Or it can be that the resistance in system is too high - something is blocked - some parts of the engine are not properly lubricated.
I will check the gauges. It is a G1000, wish me good luck.
If the gauge is OK, the problem is bigger. Did you hear in the past about blocked pipes?
The oil pump must have enough capacity to press the oil through the pipes at idle RPM to lubricate all the places. That's the low limit.
At high RPM the pumped volume will cause pressure to be still below the top of green arc, if the oil has normal viscosity. That means at RPM on top of green the pressure will be in green (always was in my engine). If the oil is cold, the resistance in pipes is high, pressure would rise to the top of green arc and that's the point where the limiting device the PRV will kick in and cut of the excess volume to keep the pressure at the set value. Until this moment it is completely closed. Technically it is a D-type regulator (D=derivating, other types are P=proportional and I=integrating).
If during the normal operation let's say 2350 RPM and warm engine the oil pressure was at ca. 60 psi before and now it is 90 psi, that is a signal something is wrong. It can be the gauge. Or it can be that the resistance in system is too high - something is blocked - some parts of the engine are not properly lubricated.
I will check the gauges. It is a G1000, wish me good luck.
If the gauge is OK, the problem is bigger. Did you hear in the past about blocked pipes?
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Single Grade Ashless Dispersant Oils - No general rule exists for every engine type when choosing the correct grade of oil; however, based on the average ambient outside temperature at engine start-up the most common grades are SAE 40, SAE 50 and SAE 60, which equates to AeroShell Oil W80, W100 and W120 respectively.
Traditionally, the choice is associated with climatic zones - AeroShell W80 for cold climate regions (-17 - 21°C), AeroShell Oil W100 for temperate regions (15 - 30°C) and AeroShell Oil W120 for warmer climates (above 26°C).
It maybe that you have gone from a SAE40 (W80) to the multi-grade. What was the previous oil?
Is the CHT & Oil Temp normal?
Traditionally, the choice is associated with climatic zones - AeroShell W80 for cold climate regions (-17 - 21°C), AeroShell Oil W100 for temperate regions (15 - 30°C) and AeroShell Oil W120 for warmer climates (above 26°C).
It maybe that you have gone from a SAE40 (W80) to the multi-grade. What was the previous oil?
Is the CHT & Oil Temp normal?