nels Posted December 17, 2018 Report Share Posted December 17, 2018 1 hour ago, jetdriven said: Old wives tale. The regulator simply dumps excess oil above a certain pressure. Ok, that makes a lot of sense. Quote Link to comment Share on other sites More sharing options...
nels Posted December 17, 2018 Report Share Posted December 17, 2018 On 12/14/2018 at 7:53 AM, N201MKTurbo said: The oil pump is mounted to the accessory case. The inlet passage is cast into the accessory case and the sump. The passage passes through the sump gasket at the back of the sump. If that gasket seal is not perfect, it could be sucking air in at the gasket. I’m not sure if the oil level in the sump is above that gasket at 6 quarts or not, you can see if it is by taking the dipstick out and holding it next to the dipstick tube and seeing where the 6 quart line is. My mind always goes back to an automobile engine as I’ve never had an aircraft engine apart. A typical auto engine would have the pickup mounted from a tube that would go to the oil pump. I had invisioned a leak or crack in this tube at the 5 1/2 quart line. I assume this tube does not exist but is rather part of the case and sump. What is mentioned above makes a whole lot of sense. If the gasket between the two parts is leaking it would be sucking oil above a certain level and air below that level. Maybe the joint between the accessory case and the sump just needs to be tightened up? I have no idea how difficult that might be or if it can be done? Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted December 17, 2018 Report Share Posted December 17, 2018 3 hours ago, nels said: My mind always goes back to an automobile engine as I’ve never had an aircraft engine apart. A typical auto engine would have the pickup mounted from a tube that would go to the oil pump. I had invisioned a leak or crack in this tube at the 5 1/2 quart line. I assume this tube does not exist but is rather part of the case and sump. What is mentioned above makes a whole lot of sense. If the gasket between the two parts is leaking it would be sucking oil above a certain level and air below that level. Maybe the joint between the accessory case and the sump just needs to be tightened up? I have no idea how difficult that might be or if it can be done? Not a bad idea. There is a line of 7/16 bolts at the parting line. Retorque them to the specified torque. Cheap and easy. Quote Link to comment Share on other sites More sharing options...
marcusku Posted December 18, 2018 Author Report Share Posted December 18, 2018 10 hours ago, nels said: My mind always goes back to an automobile engine as I’ve never had an aircraft engine apart. A typical auto engine would have the pickup mounted from a tube that would go to the oil pump. I had invisioned a leak or crack in this tube at the 5 1/2 quart line. I assume this tube does not exist but is rather part of the case and sump. What is mentioned above makes a whole lot of sense. If the gasket between the two parts is leaking it would be sucking oil above a certain level and air below that level. Maybe the joint between the accessory case and the sump just needs to be tightened up? I have no idea how difficult that might be or if it can be done? I was originally picturing the same thing too. If you do a search on IO-360 oil sump and accessory case you can get a better visual on how it's put together. There are some drawings in this PDF that help too: http://www.rvplane.com/pdf/XP360_OverhaulManual.pdf So is it safe to say that what myself and a few others are experiencing is abnormal? Are there others who have run have run 5 qts who see the same pressure as at 7 qts? Quote Link to comment Share on other sites More sharing options...
Guest Posted December 18, 2018 Report Share Posted December 18, 2018 If air is leaking in when the oil level drops below the parting line at the sump, wouldn’t oil leak out when the level is above the parting line? Clarence Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 18, 2018 Report Share Posted December 18, 2018 Why the old wives tail makes sense... 1) Anyone with a hose and a spray nozzle sees the pressure rise as the flow after the nozzle decreases... Why this isn’t the same with the airplane engine... 2) The gear pump mostly delivers the same volume of oil based on rpm.... your hose doesn’t have this expensive volumetric device... 3) it can really pump the same volume with high pressure or low pressure at the end of the gallery... 4) Technically there is a small limitation pumping against high pressue, caused by leakage back through the pump. The leakage increases with wear of the pump gears and case wall.... Overall... 5) the volumetric flow of oil is set by the pump and rpm... 6) the pressure is set by the adjustable valve at the end 7) the bearings are tight enough that the oil escaping through them isn’t enough to change the pressure and volume running through the system... 8) As the bearings wear, the oil flow through them increases... as this flow increases, adjustment of the pressure regulator may be necessary... more oil goes through the bearings, less gets dumped at the regulator valve... 9) if a bearing gets trashed and oil escaping through gets large, there isn’t enough adjustment to hold the pressure... oil distribution will change, decreasing in the other ‘tight’ bearings... 10) Chances are the bearing will start spreading metal bits... it can’t be left to continue on... 11) @M20Doc Clarence what does the oil pick-up line look like in the sump? Is it a tube, a hose or an opening in the engine case? Could it accidently start drawing air in (in this case) at 5 quarts in the sump? Sounds like an extension on the pick-up May have fallen off, or the tube has split or has a hole in it... (if there is a tube) 12) if there isn't a tube... air leaking in is less likely, as oil will leak out while the engine is not running.... PP conjecture only, I have not seen oilP change with the oil level, even in my Chevy.... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
nels Posted December 18, 2018 Report Share Posted December 18, 2018 18 minutes ago, M20Doc said: If air is leaking in when the oil level drops below the parting line at the sump, wouldn’t oil leak out when the level is above the parting line? Clarence I am thinking air is being sucked in from inside the engine crank case not from the outside. Quote Link to comment Share on other sites More sharing options...
Guest Posted December 18, 2018 Report Share Posted December 18, 2018 1 hour ago, carusoam said: Why the old wives tail makes sense... 1) Anyone with a hose and a spray nozzle sees the pressure rise as the flow after the nozzle decreases... Why this isn’t the same with the airplane engine... 2) The gear pump mostly delivers the same volume of oil based on rpm.... your hose doesn’t have this expensive volumetric device... 3) it can really pump the same volume with high pressure or low pressure at the end of the gallery... 4) Technically there is a small limitation pumping against high pressue, caused by leakage back through the pump. The leakage increases with wear of the pump gears and case wall.... Overall... 5) the volumetric flow of oil is set by the pump and rpm... 6) the pressure is set by the adjustable valve at the end 7) the bearings are tight enough that the oil escaping through them isn’t enough to change the pressure and volume running through the system... 8) As the bearings wear, the oil flow through them increases... as this flow increases, adjustment of the pressure regulator may be necessary... more oil goes through the bearings, less gets dumped at the regulator valve... 9) if a bearing gets trashed and oil escaping through gets large, there isn’t enough adjustment to hold the pressure... oil distribution will change, decreasing in the other ‘tight’ bearings... 10) Chances are the bearing will start spreading metal bits... it can’t be left to continue on... 11) @M20Doc Clarence what does the oil pick-up line look like in the sump? Is it a tube, a hose or an opening in the engine case? Could it accidently start drawing air in (in this case) at 5 quarts in the sump? Sounds like an extension on the pick-up May have fallen off, or the tube has split or has a hole in it... (if there is a tube) 12) if there isn't a tube... air leaking in is less likely, as oil will leak out while the engine is not running.... PP conjecture only, I have not seen oilP change with the oil level, even in my Chevy.... Best regards, -a- Your IO550 uses a pick up tube with a screen at the end, not removeable or cleanable. Lycoming Engines draw oil through a screen similar to a cigar, which can be removed and cleaned. Clarence Quote Link to comment Share on other sites More sharing options...
Guest Posted December 18, 2018 Report Share Posted December 18, 2018 1 hour ago, nels said: I am thinking air is being sucked in from inside the engine crank case not from the outside. Possible I guess, but hard to confirm short of dropping the oil sump to look at the gasket. Clarence Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 18, 2018 Report Share Posted December 18, 2018 Thanks go to Clarence for the descriptions of the oil pick-ups! To follow with an experiment.... a PP kind of experiment... fill the engine with oil to the 4qt line, see what the effect is on oilP... Add another quart to the 5qt line, see what the effect is on oilP... (duplicating the prior experience) Add another quart to the 6qt line, see what the effect is on oilP....(again duplicating the prior experience) We PPs are expecting very little change of oilP flying around the pattern, using the same MP, mixture and rpm... The initial finding was there was an oscillation in oilP with 5qts... With 4qts, does the oscillation get worse? Realistically, as a PP, I am only looking at an analog gauge with a needle in the green zone. There could be a lot of oscillation based on the mechanics of these systems. Normal oddities that go mostly unnoticed until a digital gauge supplies actual numbers.... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
nels Posted December 18, 2018 Report Share Posted December 18, 2018 If there is a leak in the gasket, I would think an oscillation would happen when the oil was at the gasket line due to oil sloshing back and forth over the leak spot. As the oil went under the line the pressure would stabilize at a lower pressure. If the vent tube was partially plugged wouldn’t the crankcase pressure rise and push more air through the hypothetical gasket leak? The pressure difference from the intake side of the pump to the pressurized oil pan would be even more significant. Maybe cleaning the vent tube would help? Quote Link to comment Share on other sites More sharing options...
nels Posted December 18, 2018 Report Share Posted December 18, 2018 7 hours ago, M20Doc said: Possible I guess, but hard to confirm short of dropping the oil sump to look at the gasket. Clarence Clarence, what do you think about verifying the torque on the 7/16 inch screws as suggested by N201MKTurbo? Quote Link to comment Share on other sites More sharing options...
Guest Posted December 18, 2018 Report Share Posted December 18, 2018 4 minutes ago, nels said: Clarence, what do you think about verifying the torque on the 7/16 inch screws as suggested by N201MKTurbo? Checking the torque won’t hurt. 96”lbs for the 1/4”-20 bolts and nuts as I recall. Clarence Quote Link to comment Share on other sites More sharing options...
marcusku Posted December 19, 2018 Author Report Share Posted December 19, 2018 Another observation today, prior to the flight I added oil to bring it back up to approximately 6 qts. During the flight I saw a constant 79 psi. Then at the end of the flight, on the way down I hit some turbulence and shortly there after noticed the gauge fluctuating, then looked at the JPI and it was showing between 70-75 psi. Once I was bouncing around less it seemed to stabilize at about 75 psi. Landed and checked the oil about 7 hours later and found the level to be ~5.75 quarts. For the way home I added another quart and the pressure was constant. Before I left I attempted to line up the dipstick along side the case but it's really tough to tell where the joint between the sump and the accessory case line up relative to the dipstick. Can't confirm but it seems as though the issue is with the joint in question, just seems weird that it would only be leaking from the inside only. The sump bolts do look tricky to get at if one wanted check the torque. To remove the sump to replace the gasket looks like a lot of work--time, aka $$. Quote Link to comment Share on other sites More sharing options...
nels Posted December 19, 2018 Report Share Posted December 19, 2018 2 hours ago, marcusku said: Can't confirm but it seems as though the issue is with the joint in question, just seems weird that it would only be leaking from the inside only. The sump bolts do look tricky to get at if one wanted check the torque. To remove the sump to replace the gasket looks like a lot of work--time, aka $$. Inside the case will be higher pressure than outside the case due to blow bye past the rings. So maybe that’s why it only leaks from inside out? If the vent is plugged or restricted the inside pressure would be a lot higher. Quote Link to comment Share on other sites More sharing options...
PT20J Posted December 19, 2018 Report Share Posted December 19, 2018 On 12/17/2018 at 5:53 PM, marcusku said: So is it safe to say that what myself and a few others are experiencing is abnormal? Are there others who have run have run 5 qts who see the same pressure as at 7 qts? I gererally have run Lycoming O-360 and IO-360 engines between 6 and 7 qts. Probably have a couple thousand hours behind them and never saw oil pressure fluctuations as you describe. Last summer I ferried a M20J that was burning about a quart every 2 hrs and saw the oil pressure decrease to the top of the yellow (60 psi). Checked the oil level after landing and it was 4 qts. Added three qts and it was fine. I’d try running it between 6 and 7 qts, and if everything is OK, just operate it that way and don’t worry about it. If you do go tightening bolts, check the torques in the Lycoming manual. Some engine bolt torques are different than general bolt torques. Skip Quote Link to comment Share on other sites More sharing options...
Guest Posted December 19, 2018 Report Share Posted December 19, 2018 7 hours ago, nels said: Inside the case will be higher pressure than outside the case due to blow bye past the rings. So maybe that’s why it only leaks from inside out? If the vent is plugged or restricted the inside pressure would be a lot higher. That is a really good thought. I’ve seen fuel pressure rise when the crankcase breather got blocked. Certainly worth checking the vent tubing, or air oil separator if installed. Clarence Quote Link to comment Share on other sites More sharing options...
marcusku Posted August 23, 2019 Author Report Share Posted August 23, 2019 Earlier this year I was at an engine shop that had an IO360 sump laying around so for fun we poured 6 quarts of liquid to see what level that equated to. Turns out 6 quarts brings you to very close to the top of the sump. Of course while the engine is running not all the oil is in the sump but not sure how level the engine sits while in cruise? I noticed that the pressure fluctuations are first noticeable when descending which supports the theory since the engine would be tipped more forward during a decent lowering the level of oil in the sump at the back of the engine where that joint would be. At any rate I'm all but concluding this is where my problem is. Since it would be quite costly to replace that gasket, my short term solution is simply to keep plenty of oil it. 1 Quote Link to comment Share on other sites More sharing options...
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