Crankcase pressure measurement

[Mooney-Shiner]

Since I started flying more often, I recently began noticing the oil consumption. Losing about 1 qt every 5-6 hrs and my engine bay is messy (muffler is dry).  So I began suspecting a blow by and wanted to test the crankcase pressure before I started considering anything more drastic and expensive.

Since I didn't have a spare oil filler cap to repurpose as pressure outlet for my Bluetooth manometer (https://www.amazon.com/gp/product/B07JYXR24F/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1), I build a depicted contraption seal off the oil filler tube best I can.

The Lycoming doesn't have a guidance on pressure reading, but Continental does have SB M89-9. There it prescribes the maximum crankcase pressure at 4.0 inches of water pressure (or 0.144365 PSI). 

I did several ground full power runs. My resulting reading were nowhere near this number during the ground full power run. At the highest, it was 0.63 in H2O. 

So I ruled out the static excessive crankcase pressure, and thinking of possible ram-air from the front propeller seal leak? Parallel to this effort I will clean the engine bay and try to find locations of oil leaks. I know for sure that I'm losing some oil from the top spine connection on the engine halves (possibly break out the old JB weld epoxy?).

 

Anyone found the way to test the overpressure in flight?

One strange thing to note: after running the engine for about 30-40 min, my oil cooler temperature was only 84F.  Not sure what temp should I expect? 

Edited January 5, 2022 by ukrsindicat@yahoo.com

[ArtVandelay]

One strange thing to note: after running the engine for about 30-40 min, my oil cooler temperature was only 84F.  Not sure what temp should I expect? 

Make sure you aren’t missing a digit, should be closer to 184°F.

[Mooney-Shiner]

Just now, ArtVandelay said:

Make sure you aren’t missing a digit, should be closer to 184°F.

Thats what I figured...I was able to put my hand on the cooler fins without any issues. Maybe because I didn't run the engine long enough to get the oil con enough. It was showing 160-170F on the oil temp gauge on the cluster.

Perhaps, I should measure the oil cooler temp after my next flight.

[markgrue]

Did you notice anything coming from the vent tube?   If you have a lot of blow by that is were you would see it.   The oil cooler will not get hot until the vernatherm closes.  Probably close to 200 depending on where it is set.

 

Mark 

[Mooney-Shiner]

1 minute ago, markgrue said:

Did you notice anything coming from the vent tube?   If you have a lot of blow by that is were you would see it.   The oil cooler will not get hot until the vernatherm closes.  Probably close to 200 depending on where it is set.

 

Mark 

The underbelly next to the breather drain pipe has some stickiness to it, but not excessive like some report (oil mess all the away to the spar or tail).

The vernatherm makes perfect sense. I will check my cooler after the next flight.

Thank you

[PT20J]

9 hours ago, ukrsindicat@yahoo.com said:

The underbelly next to the breather drain pipe has some stickiness to it, but not excessive like some report (oil mess all the away to the spar or tail).

That sounds about like my factory rebuilt with about 280 hours on it. Burns about 12 hours/qt. You might try switching from straight weight to 20W50. I did that and my oil consumption improved by around 4 hours/qt. On the other hand, I know people that went the other way and got an improvement. So, whichever type you are using, you might try switching and see what happens. 

[Prior owner]

You can permanently ruin the case by applying JB weld, as the case may be damaged later when it is time to remove it. I wouldn’t go that route…. Save the JB Weld for automotive repairs!

[Mooney-Shiner]

11 hours ago, PT20J said:

That sounds about like my factory rebuilt with about 280 hours on it. Burns about 12 hours/qt. You might try switching from straight weight to 20W50. I did that and my oil consumption improved by around 4 hours/qt. On the other hand, I know people that went the other way and got an improvement. So, whichever type you are using, you might try switching and see what happens. 

Wow, your oil use actually sounds great! 

I will try to use 20W50, even though I live in pretty warm climate (Florida). Parallel to this, I need to find a good way to completely degrease the engine bay and use baby power to locate the oil leak.

[Mooney-Shiner]

1 hour ago, PilotCoyote said:

You can permanently ruin the case by applying JB weld, as the case may be damaged later when it is time to remove it. I wouldn’t go that route…. Save the JB Weld for automotive repairs!

Thank you, Coyote. In your experience, how did the JB weld damage the aluminum case? I'm not questioning your comment, but just trying to wrap my head around the problem at hand.

[Prior owner]

I’m not saying that it will ruin the case when you apply it, rather, I’m saying that to get it all off later at overhaul time, that it can be very tenacious stuff…to the point that chipping it off of aluminum might require a metal chisel. I have used it to repair things like transmission housing ears and speedo drive towers that had broken off… and the repairs have lasted for years. If the surface is prepped properly, it really doesn’t want to come off later.
 

I was just thinking about the next guy. Using pro-seal eliminates this possibility. Use my opinion, though.

[201Steve]

On 1/6/2022 at 10:32 AM, ukrsindicat@yahoo.com said:

Wow, your oil use actually sounds great! 

I will try to use 20W50, even though I live in pretty warm climate (Florida). Parallel to this, I need to find a good way to completely degrease the engine bay and use baby power to locate the oil leak.

Avgas

[larryb]

I like the idea of actually measuring the crankcase pressure. But isn’t there a separate vent? Did you plug that? And does your oil filler adapter have a perfect seal?

When I had my J I learned to be happy with oil consumption in your ballpark. I found that I got somewhat better consumption when doing long cross countries and worse consumption when doing approach after approach during my instrument training.

[carusoam]

There is a procedure for measuring crankcase pressure…

It typically uses an old air speed indicator…. And gives pressure ranges in mph…

 

If you are experiencing blow by… and oil usage…

Expect that the oil will turn black quickly….

The oil tends to foam a lot…. With exhaust bubbles entrained in it…

The increased volume and bubbles exit the drain tube…

The oil also takes on a nice exhaust aroma to go with that…

The usual exit for the blow by exhaust is the drain tube at the back of the engine…

If quarts are going out the tube… the oil will be on the belly all the way back to the tail tie down….

 

If the oil is going out with the usual exhaust…

the lower plugs are usually coated as a sign…

The oil exits the exhaust valve and nicely drips out the end of the exhaust pipe… or leaves a burnt stain back there, that doesn’t belong…

 

Sounds like an extra quart is getting away somehow…. If thrown into the cowl, it often finds its way out the front of the inlets… and drops appear on the windshield… very thin layer of what used to be a drop..

 

PP fuzzy memories of old times only…

-a-

[Guest]

I’ve never seen a published crankcase pressure value for a Lycoming engine.  I once had a Lycoming engine which had very high fuel pressure after the engine was re-installed after a repair.  We verified the high pressure with a second fuel pressure gauge.  After much head scratching we found a plastic line plug in the breather hose, it had been installed to keep the line clean, but had migrated down the hose blocking it.  The excess crankcase pressure biased the pump diaphragm raising the pressure.

Clarence

[Mooney-Shiner]

2 hours ago, M20Doc said:

I’ve never seen a published crankcase pressure value for a Lycoming engine.  I once had a Lycoming engine which had very high fuel pressure after the engine was re-installed after a repair.  We verified the high pressure with a second fuel pressure gauge.  After much head scratching we found a plastic line plug in the breather hose, it had been installed to keep the line clean, but had migrated down the hose blocking it.  The excess crankcase pressure biased the pump diaphragm raising the pressure.

Clarence

Exactly, there is no Lycoming SB on crankcase pressure. So I used the Continental SB as referenced above. Also there was a guidance on using old airspeed indicator. But since I don't have old airspeed indicator laying around, I used the manometer and measured it in inches of water as per Continental SB.

I did check my breather line and it seemed unobstructed.  I didn't block the breather line during the test, because I wanted to measure the normal operation pressure in the normal configuration.

Thank you for the  feedback, guys.

 

[takair]

Was the oil burn better and suddenly got worse or did you just notice what it is now? 5-6qts per hour for your engine is not terrible or out of line.  While you have some oil on the engine, I suspect that is not the primary source of your oil consumption.  In other words, even if you fix that seepage, I suspect your burn rate won’t be that much better.  Consider PRC….like used for fuel tanks….on the spine, vs Jb weld.  Easier to remove later.  Be sure the spine bolts are torqued.  They do tend to loosen over time.  An overpressurised case, which is rare….will sometimes spray from the nose case seal….and can blow it out  if it is the bonded type.  The upper spine usually only has splash oil.  In other words, if the case was overpressurised, I suspect you would see other symptoms.  If you have oil drops from the vent, you are likely ok…..or just blow through it and listen in the oil fill to be sure….don’t forget to temporarily plug the whistle slot first.

[EricJ]

4 hours ago, M20Doc said:

I’ve never seen a published crankcase pressure value for a Lycoming engine.  I once had a Lycoming engine which had very high fuel pressure after the engine was re-installed after a repair.  We verified the high pressure with a second fuel pressure gauge.  After much head scratching we found a plastic line plug in the breather hose, it had been installed to keep the line clean, but had migrated down the hose blocking it.  The excess crankcase pressure biased the pump diaphragm raising the pressure.

Clarence

Since the breather is open to atmosphere, the expected average crankcase pressure would be ambient pressure plus or minus whatever small delta the flow through the breather creates.   If the flow through the breather isn't large, then the delta would be expected to be small.

Crankcase pressure as a diagnostic should be useful only for finding breather blockage in an open system.   In a closed or highly restricted system it might be more useful if there was guidance on what was normal or not.

[David Lloyd]

Continentals on a Bonanza would have a high crankcase pressure if the front crankshaft seal was leaking.  I had one seal leak in thousands of hours, several engines.  It caused a lot more oil than normal to exit the breather.  The oil dripping of the tail skid made it obvious something was going on.  Another cause of high crankcase pressure could be from a large amount of piston ring blowby. Again, a lot more oil than normal would exit the breather.  Blocking or restricting the breather would blow out the front crankcase seal.  You would notice the big oily mess.  Some people said that repositioning the breather outlet could suck more oil out of the crankcase making for an oily mess.  Without the oily mess, I would look for another cause of high oil consumption.

[carusoam]

Check to see if you have the right case vent / breather line…

It is specific for a few things that include the whistle hole, location and orientation…

And it’s length going out into the slipstream…

 

If this tube got replaced by a lower cost tube… it may turn into an oil sucker at speed…

A lot of engineering went into the design of this tube… 

-a-

[Yetti]

You could take the case bolts out around the leak and very small amount of Permatex #3 in the bolt hole.   I had one mechanic suggest this and one mechanic think it not a good idea.   But it stopped leaking at the case half seam.

[Mooney-Shiner]

Update:

I cleaned the engine, did a run up and checked the engine with borescope. One particular area stood out. I uploaded some of the short videos on the youtube:
https://youtu.be/JhoQeoxQZ-A
https://youtu.be/a-M1RDtYfSw
https://youtu.be/JgS2SW9HNOw

It looks like the gasket of prop governor(between the governor and crankcase) is leaking. I think it lightly misting the magneto above and drains below on the sump/crankcase horizontal seam and on the suction screen cap. I'm not sure what I can do there.

The other area that I noticed to be oily is the bottom case halves bolts, forward of sump and between the starter and alternator. Not an easy place to reach at, but I will try to get in there and re-torque the 1/4 inch nuts at the crankcase bottom parting face to 98-108 inch pounds as per overhaul manual.

Edited February 12, 2022 by ukrsindicat@yahoo.com

[A64Pilot]

If your going to retorque the case halves (a much, much better idea than any kind of sealant) Retorque them all,  see if there is a sequence in the manual.

If your case is leaking, it’s entirely possible it’s fretting which will over time ruin the case

Edited February 12, 2022 by A64Pilot

[flyingchump]

My engine looked like that when I bought my plane.  I had 3 main oil leak areas:

1) I found 3 crank case half bolts that were not tight at all.  I could turn then with fingers... SO I had oil seeping out from the halfs. They were the 3 hardest bolts to get a wrench on so I knew the previous maintainers were just lazy.  After finding this I retorqued every single bolt on the crankcase halfs and the oil sump.  It took longer than you'd think but it was worth the peace of mind and stopped a lot of oil.

2) I replaced all 4 of the oil return line hoses.  There are 4 little 2-3 in sections of rubber hose under the cylinders (2 per side) .  The rubber gets subjected to the heat from the cylinders so should be replaced often anyway.  2 of mine were leaking (very slowly) but the oil was blowing everywhere and making a mess.

3) My biggest oil leak was the gasket under the oil filter adapter housing which is immediately above the governor.  Like you, I was sure my leak was coming from the governor but it was higher and I just couldn't see it.  There is not a lot of room back there so I bought a cheap-o borescope camera from amazon.  I was able to navigate that little thing back there and find the leak.

Maybe my story can help you.  Good luck.

[Mooney-Shiner]

On 2/12/2022 at 9:01 AM, flyingchump said:

3) My biggest oil leak was the gasket under the oil filter adapter housing which is immediately above the governor.  Like you, I was sure my leak was coming from the governor but it was higher and I just couldn't see it.  There is not a lot of room back there so I bought a cheap-o borescope camera from amazon.  I was able to navigate that little thing back there and find the leak.

Thank you, FC. I went ahead and looked around the oil filter adapter housing with my articulating borescope and it seemed to be dry to me. Video posted:

I will keep looking.

I also asked Savvy Aviation Q/A and they offered that my Hartzel H-1 prop governor leaks because it doesn't have two P/N 72053 gaskets sandwiching the LW-12347 propeller governor pad plate as per Lycoming Service Instruction No. 1438A. I think this mod was already mentioned couple of times here on the board.

Separately, I re-torqued the top 1/4" bolts to Lyc overhaul spec and applied high torque RTV on the leak on the top mating seam of two case halves. It held up pretty good during the ground runups. However, when I went to do some pattern work, I noticed that the oil was once again pushing through the RTV.

So now my plan is to clean up this area really well from all the oil/RTV/impurities. Then reapply the RTV or ProSeal,  while putting a ShopVac in the dipstick tube to create the negative pressure inside the crankcase to pull the RTV further in the opening between two halves.   

   

[Mooney-Shiner]

On 2/12/2022 at 8:47 AM, A64Pilot said:

If your going to retorque the case halves (a much, much better idea than any kind of sealant) Retorque them all,  see if there is a sequence in the manual.

If your case is leaking, it’s entirely possible it’s fretting which will over time ruin the case

I will check for fretting. From brief cursory google, it seems that "smoking gun" of fretting is a difficulty to turn the prop immediately after the shutdown of the engine due to binding. I don't think that I have that problem, but I will double check it tomorrow.