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Oil Pressure

Manchu16

Active Member
Carb'ed O-320-E2C. Oil pressure has always been 60-65 PSI in cruise and gets into the 35-40 PSI range at idle when landing since I have owned it (2 years). Peak pressure when cold never gets above 65 PSI during warm up (Heated hanger during winter). Mechanical gauge confirms the vans gauge is within 5-10 PSI (normally lower) throughout the full range, 10-100 PSI. If you saw my oil temp post, my oil temps sit around 150F

I had a 61084 spring with 5 washers in the tall tower. I bought a new 61084 spring to make sure it had not lost strength over the years and replaced the 5 washers. Same pressures.

I know I can go up to 9, but does adding 2 or 3 washers sound wild (7 to 8 washers total?)
 
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The pump is designed to deliver quite a bit more volume than that oil system can take and the regulator just bleeds excess volume to keep pressure below a maximum and that max is viscosity dependant. If the pump can't produce enough volume to make more than 65 PSI with the current system restrictions (i.e. bearing clearances, etc.), springs and washers will do nothing. The fact that your idle pressures are low, I suspect wear somewhere. Could be the pump or the bearings or a leak at the nose bearing due to installation, as well as a missing internal galley plug. Most healthy Lyc's will produce around 50 PSI or better at idle with hot oil. 25 is the specified minimum

pump volume is RPM dependant and rarely produces enough volume at idle to create overflow via the regulator. Meaning the low idle pressure is not a regulator issue.

How old is the engine? Lyc has gone through 3 or 4 different types of pump gears over the years due to premature wear and fracture issues. Several ADs.

Larry
 
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Additional Info

Larry,

1969 build motor. Ad 96-09-10 was done in 2001

Shop overhauled in 2002, ran for 41 hrs and removed. Put on engine test stand, tested and pickled.

Retuned to service 2009. Installed 2 washers pressure at 85 psi at 2000 RPM at 47 hrs SMOH.

All engine ADs last checked 2022.

No other log entries ref oil or washers

Currently 440 hrs SMOH, 3300 TTE

Pressure picks up to 60-65 over 1300RPM. From idle (600ish) to 1300 rpm ramps up pretty linearly.

No obvious medium or large external oil leaks. Slight leak at dipstick, oil pan gasket is moist. 1 qt every 8-10 hrs, run it 5.5 to 4.75 qts.

I appreciate your insight.
 
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Pressure pick up

Not sure if it matters, I pick up my pressure on the firewall with a 30”ish hose from the copilot side top of the engine. Sensors and gauge tests done there
 
If the pump can't produce enough volume to make more than 65 PSI with the current system restrictions (i.e. bearing clearances, etc.), springs and washers will do nothing. The fact that your idle pressures are low, I suspect wear somewhere.
Larry

Larry, I am not an expert here, just trying to learn. Wouldn’t adding two washers be a simple test to prove/disprove clearance issues?

If the pressure doesn’t increase, the relief valve strength is potentially higher than the 65 psi and look elsewhere.

If the pressure increases, you still might have wear issues but there is enough capability (pressure) in the current system to overcome those losses.

CT
 
Larry,

1969 build motor. Ad 96-09-10 was done in 2001

Shop overhauled in 2002, ran for 41 hrs and removed. Put on engine test stand, tested and pickled.

Retuned to service 2009. Installed 2 washers pressure at 85 psi at 2000 RPM at 47 hrs SMOH.

All engine ADs last checked 2022.

No other log entries ref oil or washers

Currently 440 hrs SMOH, 3300 TTE

Pressure picks up to 60-65 over 1300RPM. From idle (600ish) to 1300 rpm ramps up pretty linearly.

No obvious medium or large external oil leaks. Slight leak at dipstick, oil pan gasket is moist. 1 qt every 8-10 hrs, run it 5.5 to 4.75 qts.

I appreciate your insight.

All pressure-wise looks pretty good. My M1B has 250 hrs and just plotted some pressure vs rpm after landing with 195F oil T. The pressure ramps up linearly and at 1300 rpm pretty well matches yours within a few psi. We could get more data, oil weight, temps and plots, but yours looks pretty nominal. I would not experiment at this point for the sake of engine perfection. But if you enjoy that - no worries. Plotting P vs RPM at known temps, and hot/warm days after landing once a year (like idle to 1400) is good way of tracking bearing health for the engine.

Good collection and presentation of your data - :)
 
Larry, I am not an expert here, just trying to learn. Wouldn’t adding two washers be a simple test to prove/disprove clearance issues?

If the pressure doesn’t increase, the relief valve strength is potentially higher than the 65 psi and look elsewhere.

If the pressure increases, you still might have wear issues but there is enough capability (pressure) in the current system to overcome those losses.

CT

Yes, adding washers to see if the pressures come up is a great idea and certainly not discouraging it. However, I speculate that it won't help that much in the mid RPM ranges, maybe at 2700. The low idle pressures, to me, indcates a sub-optimal oil system, as well as the progressive decline seen. Either the pump capacity is low or too little restrictoin exists in th oil system. 5 washers is a lot, assuming he has the right spring, further pushing me to speculate on low performance.

Nothing is currently dangerous or risky, just not at levels normally seen with these engines. The fact that it is not stable seems to indicate that this is a progessive problem. 400 hour ago he got 85 PSI with two washers. Now he gets 65 PSI with a new spring and 5 washers. Not a lot here to make me think that more washers will solve it. Further progression of this, IF it occurs, are likely to appear at the idle end. If this continues, at some point there won't be enough flow at idle.

Maybe others can chime in with their experience, but I have typically seen around 50 PSI at idle on Lyc's even with hot oil. To me, 35 stands out as sub-optimal and only marginally above the minimum. The regulator is fully closed at idle (why you see the ramp from idle to 1300), so more washers here is not going to help the low idle pressures.

To be clear, I am not recommending any type of action beyond continual monitoring. Pressures currently all above specified minimums. But at some point you have to ask why is performance declining. Given the recent removal of the regulator (presuming he checked for knicks or debris), additional washers and a new spring, it is hard to see this as a regulator fault causing the decline. No way to know whether it will be stable from here on or will continue to decline. That said, if there is a broken tooth floating around in the pump, bad things could happen fast. Pretty unlikely but you just don't know. I would want to know WHY pressures have declined as that can calibrate your "worry level."
 
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Lycoming

For anyone who places any value on their Lycoming engine, I strongly recommend searching for "What Lycoming Won't Tell You" by Bill Marvel.
Among other things it explains why on Cessna 172 and 182's since the resumption of production- if the oil pressure gage reads 75# the actual oil pressure is 83-85#. Cessna had a VERY valid reason for doing this.
It is called proper valve train lubrication which with low oil pressure is seriously deficient on Lycoming engines.
With 65# on the gage measured at the standard aft gallery location, the front of that gallery is 55-57# and the left gallery measurably less.
 
Follow up and close out

BLUF - It was a bad Van’s Oil Pressure Gauge. ISSPro.

I used a known good sender and calibrated it against a mechanical gauge at 80 psi using an air compressor. About 60 ohms. I attached it to the Vans Oil Pressure gauge and it read 75PSI. I stepped away to talk with a neighbor for a few mins and after 5 minutes it fell to 60 PSI on the gauge. Still 80 psi calibrated from the compressor.

Did the same at 60 psi. It took me about 5 mins to do the set up. Gauge started at 55 and dropped to 35 within 5 mins.

I can only surmise that as the gauge was cold it would read correctly but as it warmed the resistance increased. When I tested initially, the whole test was completed in a minute or two so I completed missed it.

Replaced the gauge with NOS and guess what 75 psi during warm up, 80 psi at cruise, 60 psi at idle.

Thank you to everyone for the thoughts and ideas.
 
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