Oil Pressure Fluctuation

[Encore Driver]

Anybody else notice oil pressure fluctuations of +or- 5 PSI on TSIO-360-MB engine? My 1997 M20K Encore has done this for more than 300 hours. Installed a JPI engine monitor and it reflects the same condition. The ship gauge reads 50 PSI normally but will momentarily read anywhere from 45 to 55 PSI. The JPI normally reads 40 PSI and will fluctuate between 35 to 45 PSI. This is a continual fluctuation not a once in a while thing. I have asked the mechanics at the last 2 annuals and they have no advice. The only idea I've heard that makes sense is that the automatic waste gate for the turbo uses oil pressure from the same line that both of the oil pressure sending units are installed in so the fluctuations are generated from the waste gate movements. If others have noticed this I can let it rest.

Thanks

Steve

 

[MB65E]

What's the oil temp? Not too familier with the oil temp regulator on the continental, but on Lycomings you can see a dip when the vernotherm actavates...

-Matt

[N201MKTurbo]

Perhaps there is an air leak on the suction side of the oil pump. If it was sucking in air bubbles it would cause those kind of fluctuations. I'm not sure how you would trouble shoot it. I'm not that familiar with the continental engine. On the Lycoming the suction screen is in the sump and there is a passage that passes through the sump gasket. If the gasket was askew it could cause your problem.

Just my 2 cents worth.

[Encore Driver]

What's the oil temp? Not too familier with the oil temp regulator on the continental, but on Lycomings you can see a dip when the vernotherm actavates...

-Matt

The ships oil temp gauge reads from the back of the engine right after the oil cooler and I run it about 150 degrees. The JPI reads from the front of the engine before the oil cooler and it reads 190 degrees. Both of them are stable and are controllable via the cowl flaps.

[kortopates]

Definitely not normal. The only time I've seen this is when the oil pump began cavitating, i.e. getting air in the suction tube inlet just as M201MKTurbo said above , from the oil level getting dangerously low. With otherwise steady normal oil pressure indications, fluctuations such as what you describe that accompany increasingly lower oil pressure are sign that the oil level is dropping to the oil suction inlet tube. They're really your last warning that the turbo is pumping oil overboard from its seal going bad. Missing that warning will allow the oil pressure to drop enough that the turbo can rapidly fail. The higher your flying the faster oil can leak past the seal; down low the leak is minimal at first.   

 

I personally would not accept it. I personally have not seen a faulty oil pressure regulator cause this but that seems like a possibility in addition to air in the system. I'd want to drop the oil pan to see what could be causing this, since it really suggest something may have fallen down into the oil pan interfering with the oil inlet at the screen. Since dropping the pan is big job, and your past mechanics have not been very helpful,  I'd start with calling Bill Ross at  the TCM factory ( http://www.continentalmotors.aero/Meet_the_Team/) and relay your symptoms and see what he suggests for next steps. Hopefully he may suggest some less drastic steps that can be done first, such as maybe the pressure regulator (?). But with 2 independent oil pressure indications showing the same thing I'd expect the indications to be real and you need to find the cause and get it resolved with peace of mind. I am sure you'll find TCM over the phone to be very helpful.

 

I don't buy the turbocontroller theory since when you're not changing the power in cruise (MP, prop, fuel) and not changing the altitude the controller and wategate will have achieved pretty near homeostasis such that oil pressure changes to the wategate should be near negligible - yet you report the symptom continuously. 

[Guest]

Have you had the oil suction screen checked for blockage?

Clarence

[Encore Driver]

I may have found the remedy to this problem. The ship oil pressure sending unit is mounted at the lowest point possible within the cowling, when the mechanic installed the JPI oil pressure sending unit it was installed higher up on the engine mount. I wondered if it was possible that when the engine was shut down and the oil was thin it was backflowing into the crankcase since the sending unit was above the level where the oil line exited the case. This could allow an air bubble to form next to the sending unit, even though I had bled the air from the line previously. So I moved the JPI sending unit to the lowest point possible and bled the line again. So far the fluctuation in oil pressure are minimal( +-2PSI). I have flown about 10 hours since the change, hope that's all it was.

 

Steve

[Lood]

Pardon me for jumping on board here, but I've seen the same in my F lately. Most flights were done in very windy and severe turbulent conditions though, so I'm not sure whether those conditions had something to do with it. My oil pressure fluctuation seems to coincide with the rpm fluctuations of about 30 odd rpm. My conclusion is that the prop is "hunting" due to the changing wind speeds and turbulence?

I will do a test flight in still conditions when I get time to see how the oil pressure behaves then. Unfortunately, I don't have the OEM gauge anymore, only the EDM900. I would appreciate any idea's and I'm surely going to check where my EDM900's sender was mounted.