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Oil pressure too high

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Oil pressure too high

Old 29th Jun 2019, 17:05
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Oil pressure too high

I've been chartering a plane (engine Continental IO-240) and had to abort the flight because of oil pressure on run up being at 80 PSI (green arc is 30-60 PSI, upper limit is 100 PSI). The engine is relatively new, maybe between 100 and 200 hrs. I've been flying the same plane previously before engine was replaced and oil pressure never stayed so persistently outside of green arc. On a normal day, it used to stabilize within green arc immediately after startup. POH says oil pressure may go beyond green arc prior to reaching normal operating temperature, and also warns against applying full power at oil pressure above 70 PSI at low OAT (0 deg celsius or below), and that's about it.

Talking to another pilot who flew the same plane it appeared that the problem is known, oil pressure sits at 80 PSI and goes down in flight very slowly to slightly above 60 PSI. It appears that problem is not seen as no-go and mechanic has 'approved' the plane as good to go. I eventually suggested the owner to revert to maintenance shop to ensure that oil pressure is back where it should be. I am not a mechanic, but my common sense understanding - which is perhaps wrong - is that oil pressure above normal may indicate some latent issue in the oil system that may show up in the future in worse form. Also, if it is indication issue, then pilot has no reliable oil pressure indication which is no-go too.

It would be interesting to hear opinions on this situation. Assuming this is not an indication issue, how exactly high oil pressure has negative impact on engine operation? Also, I find POH warning on no full power above 70 PSI at 0 degree celsius or below quite interesting. Struggling to understand what would be the difference in applying full power at 0 degrees vs 20 degrees celcius when oil pressure is at 80 PSI?
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Old 29th Jun 2019, 17:58
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High oil pressure means one of two things:

1. The oil is cold
2.The oil pressure relief vale is either sticking shut or has the wrong spring.

When the oil is cold it is too viscous to lubricate properly (it won't wet to the surfaces and form protective films). That's why they tell you to wait for the oil temp to reach the operating range before running at any significant power levels, and it's also why high pressure is acceptable until the oil warms up (but noting that you shouldn't be running at much more than fast tickover until it does). oil pressure/temperature errors in very cold OAT are a concern because they may indicate that the thermostat to the oil cooler is stuck open, so the oil is not warming up and may even get colder (more viscous) when you climb into colder air. That way lies a high risk of increased engine wear/damage, and a moderate risk of catastrophic engine failure.

If it's the oil pressure relief valve that's stuck shut (or has too strong a spring due to an manufacturing/overhaul/maintenance error) then you will subject the oil system to too higher a pressure, and risk damaging the oil filters and/or blasting out any core plugs in the oil galleries. In either case the risk varies from a persistent oil leak and lack of filtering to a sudden and catastrophic total loss of oil when a core plug fails and all the oil makes a break for freedom through the resulting hole.

If this is a new or newly overhauled engine which has been like this since installation I'd be taking it up as a warranty issue with whoever supplied/overhauled it, and I wouldn't be happy flying it. I'm actually surprised that the RTS has been signed with that kind of defect.

Even if it's just an instrumentation issue it's a no-go item IMHO because, as you say, this means that the pilot cannot rely on one of his/her primary engine health indicators.

£0.00007 supplied,

PDR
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Old 29th Jun 2019, 18:41
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If the gauge is electrical, it might be a bad earth return connection, in some obscure place.
Or other electrical fault. A disconnected starter engaged light wire caused a drop in oil pressure when it shorted.
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Old 29th Jun 2019, 21:04
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I would suggest that before the oil pressure valve is adjusted/ replaced that the oil press.gauge and transmitter are check calibrated,and the filter is checked/replaced as well...You may also want to check it is using the correct grade of oil...especially after overhaul....It is important that you do not use any significant power until the oil temp. is up to 40 deg C,no matter what the OAT is....Remember,the mechanic doesn`t usually fly.......
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Old 29th Jun 2019, 21:06
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Correct grade of oil? I can't speak for the IO-240, but it's cousin the O-200 recommends 80 weight. If someone has poured in 100 weight, and it's cold high oil pressure is likely, at least until it warms up. Oil pressure spring is only an issue if the engine has been apart recently. Gauge error is certainly a possibility to investigate.
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Old 30th Jun 2019, 10:23
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Originally Posted by CFO View Post
.................. The engine is relatively new, maybe between 100 and 200 hrs. I've been flying the same plane previously before engine was replaced and oil pressure never stayed so persistently outside of green arc. ................... It appears that problem is not seen as no-go and mechanic has 'approved' the plane as good to go. ......
Had exactly this myself! And I was amazed/shocked by what it revealed. Same thing, came in to fly a plane and high oil pressure. Shut down and enquired. Usual blah of "been like this for ages", "maint have checked it so good to go", "what are you worried about?", "Been like that since the new engine went in so it's fine!" etc, etc.

Since I had the a/c booked - I just snagged it! Being an Aero Engineer the people I rented it from moaned but duly accepted it was my flying that I was giving up on so reluctantly allowed me to pop it over to maintenance. Lots of "I don't know why you did that!", "what's the problem?, .... i.e. trouble maker (a frequent charge leveled at H 'n' H ). Within an hour it was back "S". When maintenance dropped it back I just asked the Engineer who'd taxied it back over (their Boss man this time) what the "snag" had been and all was revealed. It seems all new/recon engines have the oil pressure transmitter shimmed to the max and so over-read on release. Part of the fit/runup checks is to look at the oil pressure on a test gauge once running the aircraft before release and to then remove the required no of shims until a/c oil pressure shows the test gauge pressure. Disconnect test gauge and the jobs a good ‘un! Quite simple.

There were some very red faces tho as (a) the owners clearly had never gone back to ask about it/snagged it despite their claims that they’d checked and that the Engineers were happy, and, (b), it also seemed a certain pair of bods in the Maint facility had just had a “Chat, less tea, less bikkies” with their Boss for not doing the approved install process and then signing it off! He assured me the rest was OK! Good job as, again in this case, it had flown a good number of hours (100+) since the donk change! Bonus was, when I then did a short hop in it with the time I had left for my slot – it was called an “Air Test – have this one on us!” by the owners when I got back.

Not sure about your case CFO, but I know where me money is with this one too! Cheers, H 'n' H
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Old 30th Jun 2019, 10:45
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Good story, HnH, thanks for sharing! It only confirms my happiness to do maintenance myself - "on n'est mieux servi que par soi-mÍme" as the Romans used to say - even if it confines me to a rather humble craft and corresponding humble flights.
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Old 30th Jun 2019, 10:56
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Originally Posted by Jan Olieslagers View Post
Good story, HnH, thanks for sharing! It only confirms my happiness to do maintenance myself - "on n'est mieux servi que par soi-mÍme" as the Romans used to say - even if it confines me to a rather humble craft and corresponding humble flights.
No probs Olie! I was just sad that no-one had been "professional" enough to sort it on Day 1 and that I'd had a bit of grief off the owners for snagging it .... to start with!

And no such thing as "humble craft"! Anything that gets someone off the ground should be afforded the same respect! And can be even more fun!!!! H 'n' H
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Old 30th Jun 2019, 11:47
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As far as I'm aware you can't "shim" the pressure transmitter (it's a hydraulic transducer that responds to pressure) - the thing you shim is the oil pressure release valve spring. Adding more shims puts more pressure on the release valve piston and thus increases the pressure at which it opens. I can see the logic of putting a lot of shims in for the first run to ensure a healthy oil pressure for those important first few minutes of running, but as it's the actual oil pressure which is excessive (not just the gauge reading) it should be reduced to the specified range as soon as practicable because running in that condition will have all the consequences previously described.

But I am confused - if this was a "new" engine then the oil pressure should have been set at the factory because engines have to be bench run in a dyno (actually several bench runs at a range of power settings and durations) before being released for sale. If it was an overhauled engine it should also have had a number of bench runs before release - these are certification requirements. If a new or overhauled engine was installed without a correctly set oil pressure relief valve then the company who made/overhauled it seem to have been playing fast and loose with release certificates...

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Old 30th Jun 2019, 13:27
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Originally Posted by PDR1 View Post
As far as I'm aware you can't "shim" the pressure transmitter (it's a hydraulic transducer that responds to pressure) - the thing you shim is the oil pressure release valve spring. Adding more shims puts more pressure on the release valve piston and thus increases the pressure at which it opens. I can see the logic of putting a lot of shims in for the first run to ensure a healthy oil pressure for those important first few minutes of running, but as it's the actual oil pressure which is excessive (not just the gauge reading) it should be reduced to the specified range as soon as practicable because running in that condition will have all the consequences previously described.

But I am confused - if this was a "new" engine then the oil pressure should have been set at the factory because engines have to be bench run in a dyno (actually several bench runs at a range of power settings and durations) before being released for sale. If it was an overhauled engine it should also have had a number of bench runs before release - these are certification requirements. If a new or overhauled engine was installed without a correctly set oil pressure relief valve then the company who made/overhauled it seem to have been playing fast and loose with release certificates...

PDR
Hi PDR, TBH, I'm not sure exactly which bit had the extra shims fitted (this was 20+ years ago now and I have difficulty remembering anything at all these days) so I'd not use my post ILO the Maintenance Manual.

Point was, the engine came with a full set of shims fitted (shims I do recall being mentioned) to the oil widger-thingy-ma-jig which were then removed once the donk was on the aircraft to "calibrate it" to the aircraft using a calibrated pressure gauge and that was all part of the install - hence why it was such a quick fix. But I guess my real point is, if it's wrong, don't take people's word for it being "OK" etc, etc, etc - just make a bit of a fuss and just get it sorted – or walk away! I've had a few cases where things have been plain wrong, often straight out of maint, but have taken very little time to sort. But I often have found pilots have accepted the issue without snagging them for a while until I ended up flying them!

Now, as to whether that was just the gauge system, or to take into account the effects of oil coolers etc in the system and to what the shims were fitted to etc, etc I know not – the transmitter is what my memory tells me I was told but I could be wrong. It’s the “If not right, get it fixed!” message which is important and I wanted to highlight. Sorry I can't add more to the Techie detail but, being of the LEC/AV "persuasion", I've always left the messy stuff to the Riggers/Sooties/Grubbers who appear to enjoy being up to their armpits in gunk! What’s the saying, “If there are dogs around, why bark yourself?”!!!!!

And on that last bomb-shell - hat, coat and exit sharp Left before the nasty old Riggers/Sooties/Grubbers catch up with me!!!!!!

Cheers, H 'n' H

Last edited by Hot 'n' High; 30th Jun 2019 at 13:39.
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Old 30th Jun 2019, 14:25
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Originally Posted by PDR1 View Post
High oil pressure means one of two things:

1. The oil is cold
2.The oil pressure relief vale is either sticking shut or has the wrong spring.

When the oil is cold it is too viscous to lubricate properly (it won't wet to the surfaces and form protective films). That's why they tell you to wait for the oil temp to reach the operating range before running at any significant power levels, and it's also why high pressure is acceptable until the oil warms up (but noting that you shouldn't be running at much more than fast tickover until it does). oil pressure/temperature errors in very cold OAT are a concern because they may indicate that the thermostat to the oil cooler is stuck open, so the oil is not warming up and may even get colder (more viscous) when you climb into colder air. That way lies a high risk of increased engine wear/damage, and a moderate risk of catastrophic engine failure.

If it's the oil pressure relief valve that's stuck shut (or has too strong a spring due to an manufacturing/overhaul/maintenance error) then you will subject the oil system to too higher a pressure, and risk damaging the oil filters and/or blasting out any core plugs in the oil galleries. In either case the risk varies from a persistent oil leak and lack of filtering to a sudden and catastrophic total loss of oil when a core plug fails and all the oil makes a break for freedom through the resulting hole.

If this is a new or newly overhauled engine which has been like this since installation I'd be taking it up as a warranty issue with whoever supplied/overhauled it, and I wouldn't be happy flying it. I'm actually surprised that the RTS has been signed with that kind of defect.

Even if it's just an instrumentation issue it's a no-go item IMHO because, as you say, this means that the pilot cannot rely on one of his/her primary engine health indicators.

£0.00007 supplied,

PDR
Everything he said.
If itís ďnormalĒ why isnít it in the green?
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Old 30th Jun 2019, 15:49
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Originally Posted by Hot 'n' High View Post
Point was, the engine came with a full set of shims fitted (shims I do recall being mentioned) to the oil widger-thingy-ma-jig which were then removed once the donk was on the aircraft to "calibrate it" to the aircraft using a calibrated pressure gauge and that was all part of the install - hence why it was such a quick fix.

[...]

Now, as to whether that was just the gauge system, or to take into account the effects of oil coolers etc in the system and to what the shims were fitted to etc, etc I know not
...and *my* point is that none of that should have happened AT ALL. The oil pump and the adjustable oil pressure relief valve are part of the engine change unit, not the aeroplane. For a new/overhauled engine the oil pressure should be set up for the long before installation in an actual aeroplane, because nothing in the external system (even if the existing oil cooler and oil tank were retained rather than changed with the engine) should have any effect on the oil pressure relief setting. External oil plumbing can affect oil *flow*, but not oil *pressure*, hence this claimed need to calibrate it in the aeroplane against a calibrated pressure gauge, together with this bunkum about engines "being supplied with all the shims fitted" just doesn't stand scrutiny. For a new/overhauled engine there is simply no reason why the crew installing the engine in the aeroplane should ever need to mess about with the pressure relief valve settings. There are a few engine "repairs & rectifications" which might require recalibration of the pressure relief valve itself (not the gauge) to give the correct pressure (rather than the correct reading), but that wasn't how this incident was described.

I guess what I'm saying is that you were hoodwinked into accepting a smart line of B/S as an excuse for what was actually a serious maintenance error - one that could easily have led to an in-flight engine failure and a need for a non-practice forced landing.

PDR
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Old 30th Jun 2019, 16:00
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I fitted a used, replacement engine to one of my cars. It ran fine for a couple of thousands of miles but one very cold morning immediately on starting, in a few seconds it dumped all of the contents of the sump on my driveway. After cleaning everything up (took most of the day, the inside of the engine bay was dripping with oil, let alone the mess on the driveway), I found that the oil filter canister was loose but otherwise seemingly OK. I couldn't understand why it had come loose because I work on all my own vehicles, I've been doing oil and filter changes for almost five decades and never suffered this problem before. However, seeing as the engine was almost due an oil change I simply carried out that procedure (hardly any oil left in the sump!) and fitted a new filter, this time making absolutely sure it was very secure. Two weeks later later the same thing happened again, a hundred and fifty miles from home. This time the oil filter canister base was bent, so that the "O" ring wouldn't go back in. The canister "wobbled" as I unscrewed it. The car had to be recovered on a trailer.

The only thing I could think of was that the pressure relief valve in the oil pump had stuck shut. I dismantled the lower front of the engine, took off the oil pump and sure enough, the pressure relief piston was seized solid in the closed position.

I'd hate that to happen in flight....
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Old 30th Jun 2019, 18:25
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Originally Posted by PDR1 View Post
I guess what I'm saying is that you were hoodwinked into accepting a smart line of B/S as an excuse for what was actually a serious maintenance error - one that could easily have led to an in-flight engine failure and a need for a non-practice forced landing.

PDR
LOL! Let's not fall out over this PDR! Maybe, maybe not! He (the engineer) seemed genuine when I asked. But, yes, it could all have been all BS as you say. 20 years down the line, I can't be bothered to track him down and ask.

However it mattered not to me anyway as, after all (and this is what I'm saying), it was me who was the first person in 100+ hrs to put my foot down about flying it when 100+ hrs worth of others had flown it prior to me pitching up. I snagged it as soon as I saw it - copping some sig grief in the process from the owners - who then, it turned out, had lied to all those (and me) who had had the "its' been checked by maintenance and it's fine!" line trotted out to them! Even as an AV, I wasn't buying that old gag! They were very nice to me after that .... but I moved on anyway shortly after that!

The Engineer who "hoodwinked me"(? so what if he did on the details - I never flew it in that state so it would never have killed me - only, maybe, those who flew it with the high oil pressure indication - but why did they all take it when it was out of limits?) also apologised that it had been released in that condition so he held his hand up to errors on his side and he was most displeased it had ever left his organisation. He seemed genuine - and I took what he said at face value. He also could not believe that no-one else had reported it in over 100+ hrs given the fix (whatever it was ... and I'm going to avoid any mention of "shims" from now on!!!!!) was complete in less than 1 hour. That made him annoyed too! Aviation is, after all, looking out for ourselves and others so if it was really dangerous, many, many people had ignored the chance to get something possibly serious fixed!

I don't disagree that I may have been fed a line and that maybe it was more serious than I was led to believe - immaterial to me at the end of the day. As I say, I refused to fly it and only asked a simple question and took the answer at face value when it returned. That is what I repeated earlier. But the aircraft was now "S"! If it was the case that something "really unsafe" had happened, that should have been a frank 1-to-1 twixt owners and maintenance. The likelyhood of that happening? Mmmm! One hopes lesson were learned on both sides. Hence, back to poor old CFO's dilemma. My point is, "If it's wrong, don't fly it!".

Don't wish to fall out PDR as you seem someone of "sound reason" on here! I'll let others go into the "It may be this" or "It may be that"! Off to water the garden now the sun is going down as the Boss is away for a couple of nights and her "pride and joy" has been entrusted to my not-so-green fingers. Apparently, if any plants at all die in the next 48 hrs I will be held entirely responsible and shall die a slow lingering death! Mrs H 'n' H is not to be messed with when it comes to "her garden"!

Cheers, H 'n' H
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Old 1st Jul 2019, 08:55
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Great discussion and info, thanks all! To be honest, the whole thing makes me sad when I think of it for a minute. Maintenance shop clears the plane that should have never been cleared. POH says 'oil pressure good' in before takeoff checklist, but it gets ignored. What else could possibly go wrong? Will keep an eye on the situation and will keep the thread updated for completeness.
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Old 1st Jul 2019, 11:58
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Originally Posted by Hot 'n' High View Post
LOL! Let's not fall out over this PDR!
Aw heck, me neither! Not looking to fall out or grandstand - just emphasising the point that if the PoH givens a maximum oil pressure (or anything else) then taking the mechanic's word that "it'll be all right mate, trust me" might not be an execise in good judgement!

PDR
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Old 1st Jul 2019, 13:47
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Originally Posted by PDR1 View Post
Aw heck, me neither! PDR
Phew! Glad about that!

Originally Posted by PDR1 View Post
just emphasising the point that if the PoH givens a maximum oil pressure (or anything else) then taking the mechanic's word that "it'll be all right mate, trust me" might not be an execise in good judgement! PDR
Exactly! In my case it seems that mechanics had never even been asked by the owners! All 'em lovely Green Arcs ain't there just to look pretty!

PS You'll be relieved to know the garden has survived the first 24 hours!
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Old 1st Jul 2019, 16:51
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I am not the slightest bit surprised to hear the airplane in question was flown a 100 hours with the oil pressure reading too high. One of the things I find rather discouraging is that there seems to be a significant problem with the culture in flying schools and clubs. It is IMO the toxic combination of pilots not making the effort to learn their airplane systems combined with a willingness to accept broken airplanes without complaint. Sadly it starts with instructors not doing their job

2 examples

1) A while ago I was asked to do a couple of flight instructor ratings for a local school. On the first flight in the C 150 I let the student do the takeoff and gets us to the practice area so we could start with learning how to teach Attitudes and Movements. On the way out I thought the student was doing a very good job of staying coordinated. When I took over I found out part of the problem, as soon as I let go of the controls the airplane turned sideways. In 30 years I had never seen an airplane so badly out of rig. When we got back to the school I asked the engineer what was up and she said in the year she had been there no one had ever complained . After she went through the airplane and adjusted all the control surfaces the airplane flew perfectly hands off

2) A different school and another C 150. I was asked to fill in for a sick instructor. We go out and the engine seems a bit rough on runup. The student apples full power and it is immediately obvious we are a good 100 RPM low on the required minimum static RPM so I take over reject the takeoff and taxi back. When I explain why we rejected he says "What's static RPM ? " . I snag the airplane and t turns out one cylinder has an exhaust valve that was probably only a few hours from total failure. As I am leaving the dispatcher says "Oh the instructors have been complaining that that airplane has been really doggy for weeks ! "

Bottom line learning your airplane systems is a choice.You can make the effort to really understands how things work so you know when things are not doing what they are supposed to do.....or not,and then make good decisions.

Last edited by Pilot DAR; 1st Jul 2019 at 16:55. Reason: typo
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Old 1st Jul 2019, 22:06
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Originally Posted by ShyTorque View Post
The only thing I could think of was that the pressure relief valve in the oil pump had stuck shut. I dismantled the lower front of the engine, took off the oil pump and sure enough, the pressure relief piston was seized solid in the closed position.
When I had a car dump all its oil the garage diagnosed the pressure relief valve problem immediately, the first (and only) time it happened.
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Old 1st Jul 2019, 22:10
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Originally Posted by Big Pistons Forever View Post
I am not the slightest bit surprised to hear the airplane in question was flown a 100 hours with the oil pressure reading too high. One of the things I find rather discouraging is that there seems to be a significant problem with the culture in flying schools and clubs. It is IMO the toxic combination of pilots not making the effort to learn their airplane systems combined with a willingness to accept broken airplanes without complaint. Sadly it starts with instructors not doing their job
#NotAllSchools

On the climb out I pointed out to the instructor that the oil pressure was rather higher than usual (outside the green but below the red).

He took control, flew a circuit, and we landed, lesson scrubbed.

Next time I flew that aircraft the needle was in the green.
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