D-180 Oil Pressure Question

Ironflight · #1 12-25-2007, 05:24 PM

OK folks, we had a great Christmas here at the "Mikey Upgrade Facility" (actually, we did Christmas things most of the day, took the Val up into a beautiful blue, calm, cool Texas sky for awhile...and THEN rolled Mikey out for his first start after the new panel install!), culminating in the first engine run. All went well except for a lack of oil pressure. Logic tells me that this engine was running perfectly when it rolled into the hangar, and we haven't touched a thing inside, so I KNOW it has oil pressure - but the Dynon D-180 is reading "zero", even after a three minute run which included some fast idling.

I took the 'ducer off the engine and connected it to the end of an air pressure hose, then slowly cranked up the pressure to 90 psi - the D-180 showed a maximum of 5 psi - so we know that "something" is happening. My theories are:

1) 'ducer is broken out of the box - unlikely, but possible
2) 'ducer has no oil in it, and doesn't react the same to air as it does to being filled with liquid.
3) Calibration error? There doesn't appear to be a calibration factor in the D-180 for this (the "type" is selected to "1" in the setup - it's the Dynon 'ducer)

Has anyone else got a theory, or experienced this problem? Since the 'ducer has a very tiny orifice I'm at a loss as to how to fill it with oil if that is the problem. I am going to put an analog gauge on the engine tomorrow to make absolutely certain it has oil pressure.

Paul

rvator51 · #2 12-25-2007, 05:47 PM

Hi Paul,

I believe the transducer needs a ground path if you are using the dynon transducer. If you can get a ground to the transducer somehow, it should work if thats the problem.

Ironflight · #3 12-25-2007, 06:13 PM

I've got that covered Tom - thanks for the suggestion. It doesn't have a separate ground lug like the fuel pressure sensor, and grounds through the case. Just in case, I put a separate ground to the airframe when I tested it and had no joy....

next?

rvator51 · #4 12-25-2007, 07:01 PM

HI Paul,
Hae you tried disconnecting the wire from the oil pressure transducer and measuring the resistance from ground to the terminal on the transducer with the engine stopped and the engine running? This will let you know if the transducer is working or not. You should see a big change in the resistance while running.

Ron B. · #5 12-25-2007, 07:10 PM

The problem I had two days ago with my D120 was a high reading. It would go from 75 psi. to over 98 psi. jumping back and forth. The grounds all seemed ok,( I had soldered a wire to a s.s. hose clamp and grounded the other end to the engine). All I did was loosen and re-tighten the hose clamp and the presure was 65psi. on next flight. These grounds need to be good.
Ron

AlexPeterson · #6 12-25-2007, 07:16 PM

Quote:

Originally Posted by Ironflight

SNIP
I am going to put an analog gauge on the engine tomorrow to make absolutely certain it has oil pressure.
Paul

Paul, good idea (although I agree with you, it would be bizarre if something magically happened to the oil system).

The size of the orifice would only make the reading sluggish to change up or down if the transducer is filled with air.

I think bad/wrong transducer or some scale factor needing setting.

BTW, do think about what you would do in-flight if the electronic oil pressure system tells you your oil pressure just went to zero. This is the one and only engine parameter I have mechanically backed up. I've had cars with idiot lights come one only to find out the transducer conked out. Many on this forum have had erroneous oil pressure readings in flight with various systems. The 1" round UMA gauge is a simple insurance policy against that concern.

petehowell · #7 12-25-2007, 07:34 PM

Hi Paul,

Before I started the engine the first time, I removed the oil line at the transducer and cranked the engine til oil came out at the advice of a local. I did have good pressure from the first run.

Not sure from your initial post if you did that, but thought I would throw it out there.

Ironflight · #8 12-25-2007, 08:31 PM

Thanks for the additional ideas - I have been sitting here thinking about running a direct ground tomorrow to make sure that I have no resistance built up in the system. I also know that I have oil at the transducer, because I took it off and it is "wet", so I'm not to worried about that.

Alex has a very good point about having to trust the single measurement - and I don't In the Val, and in Mikey's new panel, I have an oil pressure switch to drive the panel light directly - but I seem to have lost the part number of the one I used in the Val, and the one I picked up for this application doesn't seem to be working right yet....and I intend to have THAT working before we fly. Oil Pressure is the one parameter I really need to know is there in a Lycoming - everything else can be inferred if the engine is running.

Paul

petehowell · #9 12-26-2007, 09:15 AM

I just ordered one of these as a backup:

VDO 153-009 $30

http://www.egauges.com/vdo_bld.asp?Series=Mini_Pressure

the UMA is now over $137 at vans

http://www.vansaircraft.com/cgi-bin/...=uma-oilp-mini

AlexPeterson · #10 12-26-2007, 09:59 AM

Paul, is it possible that the unit is reading bars? That would be close to being right. There is another thread discussing something similar.