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Old 03-19-2019, 02:03 AM
rv969wf's Avatar
rv969wf rv969wf is offline
Join Date: Sep 2006
Location: Beaver, OK
Posts: 447
Default (AJ) HELP! OIL Pressure Loss when Cold and Hot

Alan Judy's Van's RV-6 with a Lycoming IO-360A1B6 fuel injected engine, CS Hartzell Prob. Approximately 750SMOH. Almost everything inside this engine was NEW except the case and cylinders, cylinders were taken .010" over with New pistons etc. All machine work was done correctly and Yellow tagged, engine was blueprinted very precisely. All clearances within factory specs at overhaul and I did the assembly so I know this engine inside and out. SMOH this engine has always had around 45psi oil pressure +- 2-3 lbs at 190F degree oil temperature at idle 750rpm. In cruise it has always had around 75 lbs +- a 2-3 lbs at 2,450 RPM with oil at 190F degree. I have always been able to maintain my oil temperature plus or minus 5-8F degrees between winter and summer via a controllable oil door, the NEW Vernatherm at overhaul has never caused a problem. Engine has had Exxon Mobil Elite 20w-50 it's entire life after rings were seated. Oil and filter has always been changed around 25-30 hours. Oil samples have always been good and oil filter has always been very clean when cut apart and inspected. Engine is preheated in cooler months so I haven't had any cold starts, I live in the Oklahoma area in the USA. I average 90-120 hours per year and fly mostly cross country with a few short trip, at times I'll close the oil air inlet to the oil cooler get the oil up too 200-210F to boil off any moisture in the crankcase for a few minutes then lower to 190F range. Compression always around 76-79 over 80 at annual.

This is what happened on my last flight, on run up, my oil pressure was normal at the time. I took a 45 minute flight and shortly into the flight I noticed my oil pressure was only 52 lbs at 2,450 RPM, 190F oil, it has always been around 75 lbs +- a couple lbs SMOH at 190F oil temp. After landing my low oil pressure light came on, my low oil pressure sending unit is a separate unit than my oil pressure sending unit and it is set at 25lbs for the light to come on, I then looked at my oil pressure gauge and it was only showing 23 lbs at idle 750RPM, 190F oil. The first thing I did the next day was take the oil filter off and cut it apart to inspect, Tempest #AA48108-2, the filter media was VERY clean with no debris. I build automobile racing engines for a living and few airplane engines so I know what to look for. Oil level in the crankcase was showing 6 1/2 quarts at this time. I have always flown after an oil change with 7 qts total and when it gets down to 6 qts I add one quart, oil burn has always been about 1 qt in 9-12 hours with my steel Lycoming cylinders SMOH. My next step, I installed a New oil filter, 1 more qt of oil added to bring the oil level close to 7 quarts total and I installed a Perma Cal Calibration test gauge directly to the right front oil gallery that is the same oil galley that feeds the main bearings that is at the right front towards the prop to compare oil pressure to the MicroVision VM-1000 cockpit oil pressure. I test ran the engine and documented the start up with oil at 48f degree cold and warming the oil up to 100F. The Perma Cal test guage read 2 -3 lbs higher than the VM-1000 cockpit gauge throughout the test from idle to 2000RPM at various oil temps, test gauge and panel oil pressure corresponded in equal amounts, slight variation but all good. Being this I eliminated the oil sending unit being a problem or possibly the oil fitting at the crankcase for the sending unit that has the .040" restricted hole from being plugged up. For those that don't know, the .040" oil restrictor is there in case the oil line breaks to slow down the loss of oil. While warming up the engine and oil, I had the same oil pressures within 2-3 lbs variation, so the oil filter was not the problem or the oil sending units. My next step was to remove the oil pressure relief, spring, ball and washers. I inspected the seat that the ball seats against in the crankcase oil galley at the #3 cylinder crankcase location, it looked good but I took the time to apply some dye, lapping compound with an old pressure relief ball and lapped the seat, it had a perfect contact pattern and was seating nicely, no issues there. The pressure relief ball had no nicks or signs of wear, I measured it with a micrometer and it was perfect. I checked the bypass spring with a NEW spring, free length was good and it had the same pressure as a new one, I went ahead and installed the new spring and noted how many shims were behind the spring and put the same ones back in. Did another ground test run, started the engine up and there were NO changes of oil pressure at different oil temps or RPMs. I'm not sure what is happening to cause the sudden loss of around 20-25 lbs oil pressure when its cold or at operating temp throughout idle to cruise RPM 2,450. If I had metal in the oil filter I'd be tearing the engine down but I don't see anything in the filter. My next step is to run the engine, warm the engine oil up, drain and take an oil sample and send in for a report. I suspected my fuel pump diaphragm might be going bad and allowing fuel into the crankcase and deluting the oil, but the vent line from the fuel pump has showed no signs of dripping or leaking, maybe the oil sample will help with this. CHT's have always been in the 300-360f range depending on outside temps. Oil temps have always been normal, no changes in fuel pressure, EGTs all good and peak the same. Timing has always been set at 20 degrees because I'm runging 10:5.1 pistons, bore scope of cylinders show no issues, no detonation issues on piston tops or ring lands. 100LL Avgas all the time, 150F -200F rich of peak in climb, cruise 75-100F rich of peak at 65-70% power. Sometimes lean of peak at low power settings. This engine has always been strong and has never had any issues and it makes a lot power. Its still strong, makes no abnormal noises and runs like nothing is wrong other than the 20-23 lbs of oil pressure that I lost across the board. Possible bearing problem? but no metal in the oil filter, possibly oil pump issues but why such a sudden loss of pressure, possibly a crack in oil gallery which if there was, oil pressure should be good cold but much worse when hot as the aluminum expands and should open up a crack in the oil gallery and making it worse at higher oil temps, but I don't think that is the case, the Woodward prop governor works fine, prop cycles normal, oil galley plug missing?, if one was missing it should have zero oil pressure. I don't see any issues with the Vernatherm as my oil heats up quickly as normal and at cruise my oil temps are normal. I have even used a thermal imaging camera to detect how the fluid/heat is flowing through the oil lines, filter and oil cooler and find no issues. Something that I have not done yet is too shim the oil pressure relief with 5 washer/ shims which should raise the oil pressure 25 lbs across the board from cold oil to hot oil for GROUND RUN TESTING ONLY to see if the oil pump will maintain as a test only. If the added shims don't show any signs of raising the oil pressure, possibly oil pump issues or something else has gone wrong inside the engine that is causing the leak of internal oil pressure. I questioned the piston oiler nozzles but they open at around 40 lbs and should not cause low oil pressure at cruise RPM. It's not a heat related issue of any sorts as I don't have any. I'm at a loss and need some professional advise before I do a teardown at 750SMOH. FYI, I used to be on this VAF forum daily on a regular basis MANY years ago and payed my dues during that time but do to life changing things I have not been on here and after posting this I need to send Doug some $$$$. Any GOOD Technical Advice would help. Thanks, Alan
Alan (AJ) Judy
Beaver, OK in NO MANS LAND
RV-6 IO360A1B6 C/S Hartz 200HP ?
Also Fly North American NAVIONs
Race car engine builder/Machinist/Fabricator 1982--present.
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Old 03-19-2019, 07:09 AM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 6,328

If I had this problem, you might be the first guy to ask about it . . certainly one of a handful.

Good to hear from you, bad it was this subject.

Either the demand its higher or the pump volume is lower. Just basics, right? You have eliminated any core issue of engine operation - no metal and proper sensing. For the pressure to change abruptly something "broke" to change either demand or supply. You mentioned that, it is solid logic.

Oil level would be up ( a lot) if it were fuel dilution.

A cooling jet can not fall out can it? I don't know that detail of this engine, some are threaded, pressed or bolted in. You would not see it in CHT's. The book shows a small plug in the oil pump housing.

Good luck with the teardown. I might start with the accessory housing to see if it is the supply side, but you already know that too. Please do let us know the ultimate cause. Maybe a loose sludge tube in a crank, a rod bearing would not last long if this is it.

Maybe your brain has processed more during the night and will have clarity today. :-)


Last edited by BillL : 03-19-2019 at 07:16 AM.
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Old 03-19-2019, 07:40 AM
Martin Sutter Martin Sutter is offline
Super Moderator
Join Date: Jan 2005
Posts: 268

Same thing happened to my engine with otherwise healthy parameters. After being unable to find the cause I called Aerosport and talked to one of their engine assembler. He advised me to remove the oil pressure regulator and meticulously clean the steel ball inside and the seat it resides in. When I took it apart I was not hopeful as the ball was only lightly tarnished but nowhere near cruddy. I went ahead anyway and cleaned it to a mirror finish with a soft cloth and some fine polishing compound. Low and behold, problem solved and pressure back to normal.👍👍👍

Martin Sutter
Building and flying RV?s since 1988 for over 4000hrs
EAA Technical Councelor
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Old 03-19-2019, 07:46 AM
mahlon_r mahlon_r is offline
Join Date: Jan 2005
Posts: 1,060

I would check the suction screen. probably ok but you should check.
To me it sounds like there is another relief valve operating in the back a hole somewhere. A internal missing 1/8 pipe plug would exhibit similar symptoms to what you have seen. If you do get to doing a teardown maybe start with the accessory housing first to check all those rear plugs. Don't think its a bearing with no metal. never saw a crack in a case have so much of an effect on the pressure.
Do you think the prop gov could have an internal leak, that is allowing it to suck up more engine oil pressure than normal but still be able to function OK? Maybe worth trying a different governor? Or getting that one checked?
Any aerobatic equipment installed? if so disconnect and re plumb and see.
Assuming you have a late style pressure relief valve tower and not a short one with a case that doesn't have the centering cage for the ball. But if you have a short tower without the cage in the case it would possibly cause symptoms like you are seeing. easy fix to install a proper tall tower and get that ball centered and functioning properly all the time.
Good Luck,
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
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Old 03-19-2019, 08:48 AM
iwannarv iwannarv is offline
Join Date: Aug 2005
Location: Olathe, KS
Posts: 483

AJ! You're back!

Hope you get everything fixed up,
Brad Brensing
RV-10 Emp/Tailcone - Complete, QB Wings - Complete, Fuse - Building, Finish Kit - May '21
Never judge a man by his trim tabs.
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Old 03-19-2019, 09:18 AM
F1R F1R is offline
Join Date: Nov 2010
Location: ____
Posts: 912

Not the cause, but it might help you track down your lost flow in the end.

FWIW, take a look at a Champion oil filter- 8 holes.
Tempest only have 4 holes.

Observation with an O-320 in an R22 is that by switching from Champ to Tempest will raise the indicated Oil Temp by 15 -20 Deg. I can only conclude it is from reduced flow volume, from the smaller cross section of only 4 oil holes. (useful for winter operations when you want to raise oil temp) Re installing a Champion filter lowers the temps to normal with no other changes.

Obviously not what you are looking for in your case, but if you install a Champion filter, the increased flow might raise your pressure slightly from allowing more flow.(unless the intake screen is restricted)

Last edited by F1R : 03-19-2019 at 09:20 AM.
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Old 03-19-2019, 09:38 AM
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rocketbob rocketbob is offline
Join Date: Jun 2006
Location: 8I3
Posts: 3,769

AJ you need to do this test to see if the problem is your main bearing. If not there are a couple of plugs you can get to inside the accessory case you might be able to check without pulling the motor.

I loaned my plate out and haven't gotten it back yet. Let me know if you want to borrow it, I'll try to get it back.

Please don't PM me! Email only!

Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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Old 03-19-2019, 10:25 AM
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Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,114

AJ, good to see you back here.

By chance do you have piston or cam squirters?

All my other thoughts for your problem have already been discussed, so nothing new to add.
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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Old 03-19-2019, 07:57 PM
jrs14855 jrs14855 is offline
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,647
Default Oil Pressure

The oil pressure at the front of the right gallery is 8-10 psi less than at the normal point at the rear of the case. So you are actually 60-62 psi in cruise.
There is a Lycoming service instruction on the oil pump body. There is a hole that is plugged with a pipe plug identical to the ones at the front of the main galleries. I would think if this plug came completely out then your oil pressure would be lower that what you have. What would the symptoms be if this plug was very loose but still in place. I don't know the answer. In any event it appears you have two separate issues. Electronic oil pressure gage is reading low and a loss from an unknown location.
Also a long shot but before teardown I would install a new ball in the pressure relief. Before you do a complete teardown remove the Accessory case and check it out thoroughly including dissembling the oil pump.
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Old 03-19-2019, 10:54 PM
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rv969wf rv969wf is offline
Join Date: Sep 2006
Location: Beaver, OK
Posts: 447

A BIG Thankyou to everyone that responded back with things to check and to look for. Somebody ask about my oiling system if it had an aerobatic inverted oiling system, NO I don't have that, standard Lycoming oiling for normal flying. One thing I did today was this, I added a total of .125" of washers behind the spring at the oil pressure bypass along with a NEW ball installed and with the new spring from the other day, fired it up and I gained some oil pressure with apples and apples oil temperatures from the other day but no where near close to what it used to be and it still fell all the way down to 29lbs at 100F oil temperature at idle around 750 RPM. I did this just to see what would happen. I'll just have to dig into the thing and find out where the leak or problem is. One thing that I am going to do is take the governor off and block it off just to eliminate it for piece of mind, probably won't make any difference but I'm game to trying anything. If it was a bearing issue, why not anything in the oil pan screen and nothing in the oil filter. When I do get the engine pulled I'll start at the accessory case, oil pump etc, then onto the oil pan, pickup etc.... Thankyou again for everyones help. AJ
Alan (AJ) Judy
Beaver, OK in NO MANS LAND
RV-6 IO360A1B6 C/S Hartz 200HP ?
Also Fly North American NAVIONs
Race car engine builder/Machinist/Fabricator 1982--present.
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