K&P S15 impact on oil pressure

[alpinelakespilot2000]

Just installed the K&P S15 and I’ve noticed a significant increase of about 5psi at full power climb and maybe 3-5psi in cruise. Curious if others have seen higher oil pressures when switching to the S15.

If you have, please comment on how much the S15 has increased your oil pressure. If this in fact happens to be a thing, I’m curious if anyone has an explanation.

 

[Richard Connell]

Yes. 2-3 PSI in cruise. IO540 W100+

https://vansairforce.net/community/showthread.php?t=216439&highlight=K&p

 

[maxmirot]

Is this a bad thing ?

 

[M McGraw]

Yes

Increased oil pressure

 

[lr172]

Pressure is regulated by a ball and spring and the pump is a constant flow type with volume directly related to RPM. The spring is matched loosely to both the volume and pressure seen to achieve the desired oil pressure. The free-er flowing filter likely increases the volume of oil going past it to the regulator and this changes the dynamics for that regulator. It can be adjusted back down via CCW rotation of the regulator screw or removing a washer, if you have that type.

 

[Freemasm]

@Larry.

More is made from a few psi delta of oil pressure than probably should. As you know, the pressure measurement is generally used as a secondary indication of flow. There is an interesting post here (couldn't find quickly) with a title similar to "What Lycoming isn't telling you". Quick summary from memory = The sense location was moved to front a gallery port (after some additional friction losses) and the setpoint was also raised.

If I ever get the time, one day I'm gonna replace that OP relief coil spring with a belleville spring stack to flatten the flow-pressure curve.

If the engine OEM thought oil pressure range was that tight/critical, they would have done the aforementioned decades ago, IMO.

 

[JonJay]

Pressure is regulated by a ball and spring and the pump is a constant flow type with volume directly related to RPM. The spring is matched loosely to both the volume and pressure seen to achieve the desired oil pressure. The free-er flowing filter likely increases the volume of oil going past it to the regulator and this changes the dynamics for that regulator. It can be adjusted back down via CCW rotation of the regulator screw or removing a washer, if you have that type.

Makes sense, but why doesn’t it increase for most folks using that filter?

 

[Freemasm]

See post 6.

Most likely due to the Oil Pressure reg spring relative position/characteristic.

Coil springs force changes with length. The adjustment/operation setpoint happened to leave the spring operating at a relatively straight part of the length-force curve; desirable for this type of application. The closer you get to fully collapsed or free length, the less linear the force happens to be.

A properly sized belleville spring stack has a very flat, very linear response.

Without getting into age/metal fatigue, etc. This is the only guess I have.

 

[alpinelakespilot2000]

I initially asked the question because even before I switched to the S15 my oil pressures were on the high side with the regulator all the way screwed out. Now with the S15 I’m up at about 95-98psi on takeoff with it only dropping to low-mid 80s in cruise after the oil has gotten above 190F or so. Definitely high on even the revised Lycoming recommendations.

 

[JonJay]

See post 6.

Most likely due to the Oil Pressure reg spring relative position/characteristic.

Coil springs force changes with length. The adjustment/operation setpoint happened to leave the spring operating at a relatively flat part of the length-force curve; desirable for this type of application. The closer you get to fully collapsed or free length, the less linear the force happens to be.

A properly sized bevel spring stack has a very flat, very linear response.

Without getting into age/metal fatigue, etc. This is teh only guess I have.

So, some folks are lucky and the change of flow still allows the regulator to operated within range. Others not so lucky, and fell out of the “flat” part of the regulator spring? Sorry if I am not understanding this correctly.

 

[Freemasm]

So, some folks are lucky and the change of flow still allows the regulator to operated within range. Others not so lucky, and fell out of the “flat” part of the regulator spring? Sorry if I am not understanding this correctly.

Mostly = yes. That's my theory anyway. You tend to get a pretty linear/straight spring response (force - delta length) towards the middle of the spring length. SO not true at the ends (collapsed vs unloaded). You can demonstrate to yourself with a stiff coil spring. Can get the first xx% of travel squeezing with your fingers and nothing more.

The operators that didn't see a (measurable) change when changing filters were probably operating near the edge of the aforementioned "straight" spring region. If test/highly accurate instrumentation were applied, you'd probably be able to see an oil system pressure change if anything in the system components (with different losses) were changed out. In the end, it's just not that critical for tight control or they'd use something else.

Had to go back and change "bevel" to "belleville" in my previous posts when referring to the spring elements. Been a long time since I had to think about it.

If somebody has a better theory or more related experience, I'm willing to learn.

 

[alpinelakespilot2000]

Looks like less than 1 in 5 are seeing psi increases. Maybe not as prevalent as I thought from quick readings of previous threads.

 

[gasman]

Let's try this...

I use Phillips X/C 20-50... No change in pressure.

 

[alpinelakespilot2000]

I use Phillips X/C 20-50... No change in pressure.

That's what I use too, year round. +5 psi change in pressure with S15. Doesn't seem to be oil type related.

 

[Fred.Stucklen]

Oil Pressure change

Wouldn't a CCW rotation LESSEN the ball spring pressure, making the oil pressure GO UP????

Pressure is regulated by a ball and spring and the pump is a constant flow type with volume directly related to RPM. The spring is matched loosely to both the volume and pressure seen to achieve the desired oil pressure. The free-er flowing filter likely increases the volume of oil going past it to the regulator and this changes the dynamics for that regulator. It can be adjusted back down via CCW rotation of the regulator screw or removing a washer, if you have that type.

 

[lr172]

I initially asked the question because even before I switched to the S15 my oil pressures were on the high side with the regulator all the way screwed out. Now with the S15 I’m up at about 95-98psi on takeoff with it only dropping to low-mid 80s in cruise after the oil has gotten above 190F or so. Definitely high on even the revised Lycoming recommendations.

Lyc has about 5 different springs for that relief (different rates and lengths). Guessing yours is one of the longer ones and why you can't get the pressure down even at the screws extreme end of travel. Swapping one length down on the spring will allow you to adjust it where you want it. Springs are rated in pounds or ounces of force per inch of travel and the Lyc SI doc gives the rate and length for each of the 5 springs. Struggle will be the paint likely worn off you spring, so no idea which one it is and therefore where to go next. My guess is yours is too long and is pre-loaded even at the screws extreme. Lot of shops don't understand this and just throw any old spring in there from the parts pile. This could slso be due to your journal / bearing clearance being on the tight side of the tolerance range and therefore requiring more bleed volume, which means a lighter or shorter spring.

 

[lr172]

Wouldn't a CCW rotation LESSEN the ball spring pressure, making the oil pressure GO UP????

Yes and no. You're not understanding how the relief works. CCW rotation relieves pressure on the spring/ball. Less spring pressure mean more oil bleeds out of the relief (because th ball more easily lifts off the seat) and therefore less pressure downstream from the relief. The spring does NOT directly set pressure. It does so indirectly by controlling how much oil bleeds off and drains back to the sump. This is also a balancing act, as overall bleed volume from the bearing journals must be factored in and why everyone is seeing different results here and why there is not a one size fits all spring; Spring length and rate has to be balanced with the bearing bleed volume and other leakage points.

 

[sahrens]

Procedure

From the Lycoming Operator's manual for the O-360

(I) Non-Adjustable Oil Pressure Relief Valve The function of the oil pressure relief valve is to maintain engine oil pressure within specified limits. The valve, although not adjustable, may control the oil pressure with the addition of a maximum of nine (9) P/N STD-425 washers between the cap and spring to increase the pressure. Removal of the washers will decrease the oil pressure.
Some early model engines use a maximum of three (3) PIN STD-425 washers to increase the oil pressure and the use of a P/N 73629 or P/N 73630 spacer between ~the cap and crankcase to decrease the oil pressure. Particles of metal or other foreign matter lodged between the ball and seal will result in faulty readings. It is advisable therefore, to disassemble, inspect and clean the valve if excessive pressure fluctuations are noted.

(2) Oil Pressure Relief Valve (Adjustable) The adjustable oil relief valve enables the operator to maintain engine oil pressure within the specified limits. If pressure under normal operating conditions should consistently exceed the maximum or minimum specified limits, adjust the valve as follows:

With the engine warmed up and running at approximately 2000 RPM, observe the reading on the oil pressure gage. If the pressure is above maximum or below minimum specified limits, stop engine and screw the adjusting screw outward to decrease pressure or inward to increase pressure. Depending on installation, the adjusting screw may have only a screw driver slot and is turned with a screw driver; or may have the screw driver slot plus a pinned .375-24 castellated nut and may be turned with either a screw driver or a box wrench

 

[alpinelakespilot2000]

Lyc has about 5 different springs for that relief (different rates and lengths). Guessing yours is one of the longer ones and why you can't get the pressure down even at the screws extreme end of travel. Swapping one length down on the spring will allow you to adjust it where you want it. Springs are rated in pounds or ounces of force per inch of travel and the Lyc SI doc gives the rate and length for each of the 5 springs. Struggle will be the paint likely worn off you spring, so no idea which one it is and therefore where to go next. My guess is yours is too long and is pre-loaded even at the screws extreme. Lot of shops don't understand this and just throw any old spring in there from the parts pile. This could slso be due to your journal / bearing clearance being on the tight side of the tolerance range and therefore requiring more bleed volume, which means a lighter or shorter spring.

Thanks Larry. I mistakenly thought only the non-adjustable valves used different springs. I'm going to take mine apart and see if I get lucky and can identify the type of spring that's in there now.

 

[alpinelakespilot2000]

Pulled pressure regulator out. No debris observed, ball bearing perfectly smooth, bearing seat in case smooth.

https://photos.app.goo.gl/MvHyteC34H4nc4bu5

I didn't measure it, unfortunately, but it definitely is/was originally a dull gold color. Does that help at all in terms of identifying the next shorter and/or softer spring that might allow me to adjust my psi downward?

 

[skylor]

I initially asked the question because even before I switched to the S15 my oil pressures were on the high side with the regulator all the way screwed out. Now with the S15 I’m up at about 95-98psi on takeoff with it only dropping to low-mid 80s in cruise after the oil has gotten above 190F or so. Definitely high on even the revised Lycoming recommendations.

Does your oil pressure instrumentation use a VDO pressure sensor by any chance?

Skylor

 

[lr172]

Pulled pressure regulator out. No debris observed, ball bearing perfectly smooth, bearing seat in case smooth.

https://photos.app.goo.gl/MvHyteC34H4nc4bu5

I didn't measure it, unfortunately, but it definitely is/was originally a dull gold color. Does that help at all in terms of identifying the next shorter and/or softer spring that might allow me to adjust my psi downward?

Need to measure it. THere is a Lyc SI that outlines the length and rate for each spring. Not sure if each spring is a different length or not. Red the SI and it should give the color for each.

 

[rongawer]

Reduction in Headloss

Think of your oil system pressure as a math equation. Your pump is the positive value, or additive, and everything else in the system is negative - or subtractive; the sum is presented on your oil pressure gauge.

The K&P Engineering S15 filter has a lower internal flow resistance, aka "Headloss", than a comparable paper element filter. Less pressure drop (differential pressure or D/P) across the filter leaves a higher "sum" at oil pressure gauge.

It's not unreasonable that changing the oil filter in a 100 PSI full pressure system reduces D/P 2-3 PSI, or increases full pressure. You would likely see a similar increase in system pressure when changing your normal paper filter as well, assuming this new pressure is below the full open relief setpoint. This is a good thing, not something to worry about.

As already mentioned, if pressure is now above your needed range, adjust your oil pressure relief valve spring setpoint.

 

[alpinelakespilot2000]

Does your oil pressure instrumentation use a VDO pressure sensor by any chance?

Skylor

I had relatively high pressures (but in the green) from the start with the original VDO from Dynon that had crept up a bit more by the time I had 300-350 hours on the engine. Switched to the first version of Kavlico to see if it was an instrumentation problem, then went to the second iteration of kavlico when the first got service bulletined. In short, higher than typical oil pressures have pretty much been with me from the start. No change by using different senders. Unfortunately I’ve not been able to adjust it downward because Aerosport Power delivered it to me with the relief valve all the way screwed out.

Now have about 575 tach hours and only in last 100 hours have I seen oil pressures creeping up to mid 90s psi on cold takeoffs, and the K15 has seemed to exacerbate that up to the high 90s psi, so that’s what’s got me motivated to figure it out.

Sounds like I need to pull my spring out again and measure it.

 

[Mconner7]

Too high?

A well known engine builder (Bill Scott) opined that a major failing of our Lycoming engines was poor upper cylinder cooling and lube. He preached that keeping oil pressure very near the maximum allowed was desirable as it added more oil at the valve train. I think the O320H series ran a very high oil pressure and mandated antiwear additive to try and fix some design flaws.

What is the collective opinion of running the oil pressure as close to the limit as we can?

 

[lr172]

A well known engine builder (Bill Scott) opined that a major failing of our Lycoming engines was poor upper cylinder cooling and lube. He preached that keeping oil pressure very near the maximum allowed was desirable as it added more oil at the valve train. I think the O320H series ran a very high oil pressure and mandated antiwear additive to try and fix some design flaws.

What is the collective opinion of running the oil pressure as close to the limit as we can?

I am a firm believer that the Lyc engineers screwed the pooch back in the 50's by not using lifters with bypass channels to feed the rocker box with oil, like EVERY other engine manufacturer since the flat head engine style (those didn't need it). Oil is used to cool the exh valves and very little oil gets there in a lyc due to this flaw. The only oil that gets there is what bleds past the clearance between the inner and outer pieces of the plunger assy. Therefore, in theory, higher OP will create more bleed flow through this clearance and send more oil to the rockers. That is in theory. Don't know if it's true or how much additional flow it would create.

FYI, it is my theory that this ss the core reason that lyc is the only engine series that suffers from sticking exh valves. Because there is no oil to cool the valves, they get hotter than they should. Lyc has tried all sorts of exotic valve alloys and fillers to address this when they should have just modified the lifters to get oil there to do it's job. When the valve guides get above the critical temp, the oil in them cokes/oxidizes and creates the black crud (hard as a rock, BTW) that closes up the clearances and leads to sticking. The reason why some get it and some don't is the fact that the clearances in the plungers are quite variable, as they are hand lapped to fit. There is even a test for this clearance in the OH manual.

Personally I think 100 PSI is too much and therefore run at 80 and just accept the crappy design for what it is. I just don't understand the risks involved in running higher, if they do exist. Mahlon once told me it was not advised and trust few beyond him on these matters. I remember back in the 80's guys used to put the high volume oil pumps in the small block Chevy's. Those pumps were run off the distributor shaft and a lot of those guys burned up the dist gears due to the extra stress. THere are usually consequences to these type of actions even if they are not obvious.

Larry

 

[penguin]

I was told by Aerosport Power to keep the oil pressure at the higher end of the allowable range on an (I)O-360-B1B.
As a FYI, if an aerobatic inverted oil system is installed the oil pressure will change significantly, I think it rises. A different spring is required to bring it back within limits. That also happen when an engine is on a dyno without an inverted oil system. When back in the airframe the oil pressure will be much higher than seen on the dyno.

 

[RV8JD]

As a FYI, if an aerobatic inverted oil system is installed the oil pressure will change significantly, I think it rises. A different spring is required to bring it back within limits.

It actually drops, but good point. A different spring may, or may not, be required.

From the Christen inverted oil system manual: