scsmith

scsmith

Well Known Member
I have an IO-360-A1A (angle valve)
I use 15W-50 oil
I normally wait for take-off power until oil is at 125F. Fairly often, I will see oil pressure on take-off of around 95 PSI, occasionally a bit higher. Especially if I have just recently changed oil, it may even go up to 100 PSI momentarily.

At normal cruise, 2400 RPM, 180F oil temp, the oil pressure is 62 PSI. When it is a bit warmer out, and normal cruise gives 190F oil temp, the pressure will be 60 PSI.

The pressures are read on my Dynon EMS D-120, and I did verify the gage reading against a mechanical gage when first installed new (3.5 yrs ago)

So here's the dilemma, I can't lower the pressure regulator setting any lower, because I am at the minimum oil pressure for cruise. But my take-off oil pressure is above the "old" max pressure of 90 PSI listed in the 1970 revision of the Lycoming operators manual. I read in another post that later, Lycoming revised that value to 115 PSI. If that's true, I probably don't need to worry.

But I am concerned that perhaps there is a problem with the setting or function of any high-pressure oil relief component? Am I in danger of blowing the front crank seal out on take-off?

Thoughts?
 
The pressure regulator acts like a pop off valve. It opens when the pressure exceeds some value. In your case, it is probably set to open at 95 PSI or so. Changing that setting won't impact your oil pressure during cruise. Take out one washer and see what happens. My guess is you'll see 5 psi less at takeoff and nothing else will change.
 
Swimming in the sump of opinion here, but I'd raise the pressure setting.

Same oil, same engine in this context. I want to see 75~80 psi in normal cruise below 190 and dipping into the upper 60's approaching max temp.

The high pressure alarm is set at 115 psi per the TCDS maximum. I wait for 100F absolute minimum post-runup, with (like you) 115F being more typical. The alarm will trip on the takeoff roll about twice a year, for just a few moments as viscosity is dropping rapidly with temperature rise. Remember, circulation is about 7 gallons per minute.

That said, is there any practical difference between what you have and my settings? Nope.

Don't worry about the front seal. It is subject to case pressure only, typical being less than 5" H2O.
 
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Low oil pressure is usually caused by excessive bearing clearances (rods/mains). I'd be less worred about the high oil pressure at start than I would be about the lower than normal pressure at normal temps. If you can't maintain 75 psi at cruise, then you may have a more serious problem.
 
oil pressure

What Dan Horton said......+ 1.

Also, engine oil pressure has nothing to do with crankcase pressure. Don't worry about you front seal.
 
Steve

I had the same problem a few months ago, called Dynon, ordered new oil pressure sending unit for the D120, installed and problem went away.

Quick and easy

RonB
 
RonB said:
Steve

I had the same problem a few months ago, called Dynon, ordered new oil pressure sending unit for the D120, installed and problem went away.

Quick and easy

RonB
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Hey Steve, RonB has a point here - I have replaced a couple of the can-type pressure 'ducers over the years on various airplanes because they tend to fail with a high bias when cold. Before I changed anything on the engine I would probably do another 'ducer cal to make sure there really is a problem.

Fundamental rule of MCC systems troubleshooting - when you see something funny, first ask how your instrumentation is lying to you....;)
 
DanH said:
Swimming in the sump of opinion here, but I'd raise the pressure setting.

Same oil, same engine in this context. I want to see 75~80 psi in normal cruise below 190 and dipping into the upper 60's approaching max temp.

The high pressure alarm is set at 115 psi per the TCDS maximum. I wait for 100F absolute minimum post-runup, with (like you) 115F being more typical. The alarm will trip on the takeoff roll about twice a year, for just a few moments as viscosity is dropping rapidly with temperature rise. Remember, circulation is about 7 gallons per minute.

That said, is there any practical difference between what you have and my settings? Nope.

Don't worry about the front seal. It is subject to case pressure only, typical being less than 5" H2O.
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Dan, my understanding is that raising the oil pressure is really just varying the setting of the pressure relief valve such that it will begin to relieve at a higher pressure. It should have no bearing on the pressure in cruise if it's below the pressure relief setting of around 95 psi. The output of the mechanically driven oil pump is fixed for a given RPM, and pressure would vary as a function of oil viscosity, temperature and downstream resistance, e.g., bearing clearance, and if pressure were to get up to 95 psi, it would begin to be bypassed by the relief valve. Just wanted to expand on your comment. :)
 
Personally I like 100-110 on takeoff when cold. At a constant RPM as is the case with an aircraft engine higher pressure correlates to higher flow, and if the oil cooler is large enough, better cooling. There is no danger of blowing the front seal off because its not pressurized with oil. A blockage in the crankcase vent will cause it to blow off.
 
Ironflight said:
...Fundamental rule of MCC systems troubleshooting - when you see something funny, first ask how your instrumentation is lying to you....;)
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"Stuff" runs downhill, and we instrumentation engineers seem to always be at the bottom to catch it...:eek: My pat answer when a test conductor questions a parameter, is "What do you want it to read?":D

Seriously, Paul is absolutely right. Unless the sensor has been checked against a standard recently, you really don't know what the actual pressure is. And "new" doesn't necessarily mean "calibrated". Case in point: when my squeezer quit setting #4 rivets, the problem turned out to be that the gauge on my new pressure regulator was reading about 25% high.:mad:
 
Pat Hatch said:
Dan, my understanding is that raising the oil pressure is really just varying the setting of the pressure relief valve such that it will begin to relieve at a higher pressure. It should have no bearing on the pressure in cruise if it's below the pressure relief setting of around 95 psi. The output of the mechanically driven oil pump is fixed for a given RPM, and pressure would vary as a function of oil viscosity, temperature and downstream resistance, e.g., bearing clearance, and if pressure were to get up to 95 psi, it would begin to be bypassed by the relief valve. Just wanted to expand on your comment. :)
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Hi Pat. You and Kyle make essentially the same point...the relief valve ball is firmly on its seat and bypasses no oil to the sump at typical cruise RPM and temperature. I think it does bypass some oil under those conditions, assuming good bearing clearances.

Two easy experiments.

It is a positive displacement pump. Turn it faster and it pumps more volume in direct proportion to RPM. Assume you're cruising at 2300 RPM with 75 psi, and then go to 2600. Does your oil pressure rise by 10% or stay at 75 psi?

If Steve raises the spring pressure (cranks in the relief valve screw or adds shim washers) and gets a cruise pressure increase, the valve was allowing bypass flow to the sump at cruise.
 
DanH said:
Hi Pat. You and Kyle make essentially the same point...the relief valve ball is firmly on its seat and bypasses no oil to the sump at typical cruise RPM and temperature. I think it does bypass some oil under those conditions, assuming good bearing clearances.

Two easy experiments.

It is a positive displacement pump. Turn it faster and it pumps more volume in direct proportion to RPM. Assume you're cruising at 2300 RPM with 75 psi, and then go to 2600. Does your oil pressure rise by 10% or stay at 75 psi?

If Steve raises the spring pressure (cranks in the relief valve screw or adds shim washers) and gets a cruise pressure increase, the valve was allowing bypass flow to the sump at cruise.
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Correct, Dan. My understanding is that cruise oil pressure would not go up in this circumstance, however, it would be a worthy experiment and I would love to know if it did, as this would indicate there is some bypass at lower pressures as you said. Hopefully someone from Lycoming or an A&P can weigh in on this. My understanding is that this is a simple poppet valve, essentially a ball bearing held against an orifice by spring pressure and until oil pressure can offset the spring pressure, no oil is bypassed. I could be wrong and would love to know for sure. :)
 
Dan H

Dan is correct, mine had only 55 PSI in cruse after the O/H, we shimmed the spring to hold the ball tighter and raised the cruise oil pressure to 74 PSI. MY IA/AP that built the engine even knew how much the oil pressure would rise for each washer installed. The pump is pumping excess oil even at cruse RPM.

An interesting point though is that I have 74 psi in cruise but not much more then this on takeoff with cold oil, maybe high 70s low 80s. So why do others have 100+ when cold?

I'm running the same IO-360-A1A as the OP. You must remember we are also spraying the bottom of the pistons with oil in adition to oiling the bearings etc. you have to have extra so you can then regulate it otherwise it would be a big **** shoot as to what the oil pressure would end up being.
 
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Russ McCutcheon said:
Dan is correct, mine had only 55 PSI in cruse after the O/H, we shimmed the spring to hold the ball tighter and raised the cruise oil pressure to 74 PSI. MY IA/AP that built the engine even knew how much the oil pressure would rise for each washer installed. The pump is pumping excess oil even at cruse RPM.

An interesting point though is that I have 74 psi in cruise but not much more then this on takeoff with cold oil, maybe high 70s low 80s. So why do others have 100+ when cold?

I'm running the same IO-360-A1A as the OP. You must remember we are also spraying the bottom of the pistons with oil in adition to oiling the bearings etc. you have to have extra so you can then regulate it otherwise it would be a big **** shoot as to what the oil pressure would end up being.
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Just went up this afternoon, I was off just a little, Takeoff 2700 rpm oil temp 97 F oil pressure was 74 psi at cruse temp at 195 the PSI was 74. so what is the deal with the big swing some see and the no swing I'm getting?
 
Russ, my question would be, have you modified your pressure relief valve in any way? Add washers, increase spring tension? Is it possible that your relief valve is set so low (like 74 psi) that it is bypassing at all times thus limiting your pressure to 74 psi? My other guess would be a faulty sensor. I would try cranking up the pressure to try to achieve near 95 psi on takeoff. This will probably reveal what your issue is.
 
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Dan is right, Pat is not.

And Russ too (except that his take-off pressure isn't high -- maybe I need to re-test my senser)

I can attest that adjusting the pressure regulator DOES change the cruise oil pressure. When I first started flying 3.5 yrs ago, my cruise oil pressure was 55 psi. I turned it in one turn. It went up to 58 psi. I turned it in another turn, it went up to 61 psi, I turned it in another, and it went up to 64 psi.

There I left it, but in a few weeks I noticed the pressure had crept back down to 58 psi, so I screwed it in again, two turns. A few weeks later, it was down again, and I surmised that the adjuster screw was vibrating and backing out. So I safety wired it. HOW MANY OF YOU HAVE THE OIL PRESSURE REGULATOR SCREW SAFETY-WIRED?

Anyway, it has stayed rock-solid ever since -- but always on the edge of 60-62 psi depending on temperature.

It is clear to me that the relief valve is bypassing some oil at cruise to regulate the pressure to the setting of the relief valve.

So you guys are suggesting I should screw it in a bunch more turns (and re-safety it). OK. But won't that raise my take-off oil pressure? I guess if Rocket-Bob doesn't mind seeing 110 psi on take-off, I won't.

What I think is going on is that the pressure relief ball+spring opens, and the pressure you get is still a strong function of temperature and RPM, because the oil pumping losses and oil viscosity determine what the pressure is upstream of a fixed orifice size (the leakage area around the ball and its seat).

Glad to hear the front seal is not vulnerable to overpressure. From my years of wrenching on cars, I had a hard time visualizing how it could be - but I read enough stories of worry that I was concerned. So thanks. I can see how a plugged breather would of course blow the seal out.

And I guess I'll test the sender again.


DanH said:
Hi Pat. You and Kyle make essentially the same point...the relief valve ball is firmly on its seat and bypasses no oil to the sump at typical cruise RPM and temperature. I think it does bypass some oil under those conditions, assuming good bearing clearances.

Two easy experiments.

It is a positive displacement pump. Turn it faster and it pumps more volume in direct proportion to RPM. Assume you're cruising at 2300 RPM with 75 psi, and then go to 2600. Does your oil pressure rise by 10% or stay at 75 psi?

If Steve raises the spring pressure (cranks in the relief valve screw or adds shim washers) and gets a cruise pressure increase, the valve was allowing bypass flow to the sump at cruise.
Click to expand...
 
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Pat Hatch said:
Russ, my question would be, have you modified your pressure relief valve in any way? Add washers, increase spring tension? Is it possible that your relief valve is set so low (like 74 psi) that it is bypassing at all times thus limiting your pressure to 74 psi? My other guess would be a faulty sensor. I would try cranking up the pressure to try to achieve near 95 psi on takeoff. This will probably reveal what your issue is.
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Yes I mentioned we added washers to bring the PSI up from 55 to 74 in cruise, I don't believe I have any problem that needs revealing, I believe mine is working correctly, the pressure regulator is regulating the pressure so it stays the same any time there is excess pressure, the gauge is working fine, it might not be 100% accurate but new oil gives a little higher pressure, the pressure is lower at idle, it's not just stuck on 74.

Yes I believe it is and should be bypassing at all times other then hot idle where my pressure drops to the low 50s, I am running multi weight oil which might help, but I see Steve is also, doesn't seem to be helping him.
 
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Another interesting thing to note about my airplane is in the summer the oil runs 197F and in the winter it runs 190F, no chasing huge temp swings from season to season like others fight, I don?t have any oil cooler shutter, I don?t do anything different from winter to summer. This tells me my engine makes adequate oil heat to keep the oil hot in the winter and the cooler works adequately to keep it from getting too hot in the summer and the vernatherm must also be working and regulating the oil temp by controlling the flow through the cooler.

Sorry if that?s a little off topic.
 
Seasons?

Well, Russ, all that proves is that you live in Oregon!:D Or, well, right across the river.

Sure, its greyer and wetter, so you can tell what the season is, but come on, you don't have much temperature swing.
 
scsmith said:
Well, Russ, all that proves is that you live in Oregon!:D Or, well, right across the river.

Sure, its greyer and wetter, so you can tell what the season is, but come on, you don't have much temperature swing.
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True enough however I fly on the hottest days and the coldest days we get, so a flight in February with surface temps below 30F and in the summer above 90F. I have been to AZ and CA in the summer with about the same results.
 
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Thanks for the education, guys! I think I understand how it works now. I guess I would compare the operation of this pressure relief valve to the way you would increase water pressure squirting out of the end of a hose by increasing pressure with your thumb over the end of the hose. So you're getting some bypass at all times and you can tighten down the spring pressure to increase oil pressure overall--not just for the upper limit. I guess I was looking at this valve as solely a pressure relief valve when in fact it is a pressure regulating valve.

So referring to the Bill Marvel and Bill Scott article sited by Bob, why wouldn't you want to increase your oil pressure right up to the maximum and get the maximum valve stem cooling as Bob suggested? I can't think of any reason why one shouldn't try this, how about you guys? Sorry for the thread drift, but I think this is an important point.
 
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Pat Hatch said:
So referring to the Bill Marvel and Bill Scott article sited by Bob, why wouldn't you want to increase your oil pressure right up to the maximum and get the maximum valve stem cooling as Bob suggested?
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Exactly why I advocate it. There really aren't any downsides in bumping the oil pressure up that we have to worry about since the pressure parameters are well tested in newer certified designs.
 
Pat Hatch said:
Thanks for the education, guys! I think I understand how it works now. I guess I would compare the operation of this pressure relief valve to the way you would increase water pressure squirting out of the end of a hose by increasing pressure with your thumb over the end of the hose. So you're getting some bypass at all times and you can tighten down the spring pressure to increase oil pressure overall--not just for the upper limit. I guess I was looking at this valve as solely a pressure relief valve when in fact it is a pressure regulating valve.

So referring to the Bill Marvel and Bill Scott article sited by Bob, why wouldn't you want to increase your oil pressure right up to the maximum and get the maximum valve stem cooling as Bob suggested? I can't think of any reason why one shouldn't try this, how about you guys? Sorry for the thread drift, but I think this is an important point.
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I only just read what Bob posted, I?m not going to do it because my engine has been very happy and in a steady-state for 1100 hours, it?s 1000 hour valve wobble test revealed that the valve guides where clean and well within spec, Also my CHTs run in the 220s in the winter and the 250s in the summer and reach 280 max on a long summer climb. My engine guy said a stuck valve is often the result of a single HEAT exposure that bakes oil in the valve guide, I don?t have valve guide wear or sticking valves or heat issues, I?m not messing with it.
 
Thanks, Russ. Yeah, at 1,100 hours I don't know if I would mess with it, but I've got about 200 hours on mine so I think I'll try bumping it up with the thought of perhaps extending valve life or preventing problems in the long run. Sounds like about +3 psi per turn on the relief valve. I'm running about 82 psi in cruise now, but rarely see above 90 psi on takeoff, so I'll try one turn at a time and see what I get after each turn. Of course it doesn't get cold here in Florida, although this morning it was 44?--very rare!

Thanks, Bob, for the informative posts and to Steve for the great thread. :)
 
Russ McCutcheon said:
I only just read what Bob posted, I?m not going to do it because my engine has been very happy and in a steady-state for 1100 hours, it?s 1000 hour valve wobble test revealed that the valve guides where clean and well within spec, Also my CHTs run in the 220s in the winter and the 250s in the summer and reach 280 max on a long summer climb. My engine guy said a stuck valve is often the result of a single HEAT exposure that bakes oil in the valve guide, I don?t have valve guide wear or sticking valves or heat issues, I?m not messing with it.
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While I agree with you 100% I don't see how your temperatures are accurate. I have a $1000 thermocouple calibrator that I've used to check a couple of probe installations, and without mentioning brands here I've found several instruments to be complete junk as far as accuracy goes.
 
rocketbob said:
While I agree with you 100% I don't see how your temperatures are accurate. I have a $1000 thermocouple calibrator that I've used to check a couple of probe installations, and without mentioning brands here I've found several instruments to be complete junk as far as accuracy goes.
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I don?t have any fancy calibration equipment, I was however suspicious just like you so I checked them in boiling water and got 213F so I think its pretty close, I can kind of back it up to by being able to leave my hand on the heads for two or three seconds right after shutting down after a flight, touching my buddy?s cylinders on his Cessna 150 that run over 100 degrees hotter will burn you if you more than just tap them. I suppose I could check them with a lazar type hand held tamp sensor after shut down and compare it to the gauge.
 
Oil pressure and bearing limits

I just got my crank back from ACSS it was at the bottom of service limits STD/STD and would tag as is. My concern was Oil Pressure and had the crank cut .003/.003 new limits as I want as much pressure getting to the lifters as possible. So for the guys who know.What do you see in the field as to engines that are new limits compared to service limits with respect to Lifter failure rates? When talking to engine shops they tell me "they see as many new lifter fail as reground units.Is this a function of Oil Pressure or how often the grinder dress's the stone?
 
rhill said:
I just got my crank back from ACSS it was at the bottom of service limits STD/STD and would tag as is. My concern was Oil Pressure and had the crank cut .003/.003 new limits as I want as much pressure getting to the lifters as possible. So for the guys who know.What do you see in the field as to engines that are new limits compared to service limits with respect to Lifter failure rates? When talking to engine shops they tell me "they see as many new lifter fail as reground units.Is this a function of Oil Pressure or how often the grinder dress's the stone?
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Assuming the lifters (cam followers I think you mean) and the cam are reconditioned properly I think the biggest factor is how often the engine is operated, engines that sit a lot have cam and follower failures, they rust and pit then you start the engine and they grind away with no oil for a bit, every time this happens the cam and followers are closer to a premature death. My cam and followers where re-conditioned in 2006 by ECI, 1100+ hours and there doing fine, as for my crank, it had 900 hours on it as far as we know and was still at the big end of new limits so we did nothing to it, cleaned, measured, visually inspected and put it back in.
 
Thanks guys!

rocketbob said:
http://egaa.home.mindspring.com/new.htm

2nd to last paragraph is the most relevant here.
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I'm really glad I finally got around to asking the original question and stimulating this discussion. At next oil change I will indeed crank up my pressure, and I will stop worrying about the high pressure at initial TO, and I'll check my pressure sensor too. But the real take-away is that more oil pressure is better, not for bearing life (because I'm sure 60 psi is enough for that) but for valve cooling.

Cool!
 
Russ McCutcheon said:
I don?t have any fancy calibration equipment, I was however suspicious just like you so I checked them in boiling water and got 213F so I think its pretty close
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Thermocouples are very nonlinear, so checking them at one temperature isn't a good check to test its calibration across its range of temperature.
 
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