Oil pressure suddenly higher

XP-360 with about 300 hours, EIS 4000 monitor. Oil pressure has always run around 80 psi. Day before yesterday it was steady at 92, yesterday was fluctuating between 96 and 99. All other parameters were completely normal, including oil temperature which was 170 degrees. The engine was running perfectly. Verified the pressure indication dropped to zero at shutdown.

Can anyone think of anything OTHER than a sensor/instrument problem that would cause this? Should I be worried?

Thanks!

My sender failed with the same symptoms.
Vic

vic syracuse said:

My sender failed with the same symptoms.
Vic

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EXACTLY what I was hoping to hear!!
Thanks Vic!

Sender failures

I agree..... when electrical indications become "sporadic", it's a signal issue. I experienced same type failures in my Long-EZ. That's exactly why I also put in a small mechanical OP gauge in my -9A as a back up indication. See pic in top left corner of panel: http://www.mykitlog.com/users/display_log.php?user=n539rv&project=161&category=3987&log=90358&row=3

My sensor went bad, too

After about 9 months, the FP sender for my Dynon unit crapped out, leading to FP readings of 99.9 at cruise settings. The FP and OP senders look identical, but are different regarding the pressures they are intended to handle.

Yes, they are different, but most automotive stores and Summit Racing have them in stock. The VDO senders are usually labeled 0-5 BAR or 75 PSI for fuel pressure (1 BAR = 15 psi, or 1 atmoshpere), and the oil pressure is 0-10 Bar or 150 PSI.

Vic

I Just Went Thru the Same Problem

Jim:
First thing was to "tee" in a pressure gage between the engine and the transducer to verify the problem is somewhere "above" the engine. If the teeded in gage reads OK and yours is still high, it might be one of four things (at least from my experience).
1 & 2. Because I was using Van's gage and transducer, I decided to replace both of them - total cost less than $80.
3. The manager of one of the largest shops at PTK to me to check my ground(s). I replaced the anodized elbow with steel, removed the transducer manifold and stripped the anodizing from the contact surfaces, ran a tap in the NPT threads to clear anodizing, then recrimped and refastened the instrument gage ground wire.
4. Removed the gage sending wire, stripped some insulation, and recrimped.
Pressure readings are now back to normal. Unfortunately, I don't know which action actually cured the problem.
Terry, CFI
RV-9A N323TP

"grounding"

There is no "ground" in an airplane; you leave that behind when you take-off. All lower voltage electrical circuits, as opposed to high-voltage sparks and corona, require two conductors - an outy and an inny. Never depend on the mounting of alternators and transducers to provide a good circuit return; always provide a metallic conductor. That's why I use twisted-pair wire for every circuit. Plus, if you use a metallic airframe as a return, you are asking for eventual corrosion at riveted joints when moisture is present. If the circuit has any pulsating high current, such as strobe wiring, you will have much less radio interference when twisted-pair is employed. You will also minimize any common-mode problems, the so-called ground-loops if you supply the return this way.

Oil Press.

My VDO sender went "TU" a while back and I replaced it with Grand Rapids' very pricey made in China sender. If you can get the mfr's part # from Sandy, you can cross-reference and order one from Digi-Key or other electronics store at a slightly lower price.

In my opinion; VDO sensors border on "junk". OK for Autos---not for use on Aircraft.

Loose connection at sender

My XP-0-360 did the same thing and it was only a loose connection at the sender. Once it was tightened it has been fine.

Hopefully it's just the sender

I had the same problem in my Cessna, but it wasn't the mechanical gauge, it wasn't the pressure regulator, it wasn't the wrong kind of oil, and it wasn't a clogged channel. Finally wound up having the engine majored (there was the possibility that pressure was high at the gauge because some parts of the engine weren't getting any oil) and the problem went away. I think...

mannanj said:

If you can get the mfr's part # from Sandy, you can cross-reference and order one from Digi-Key or other electronics store at a slightly lower price.

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Already got it: 360-004

Spruce has it for the same price:http://www.aircraftspruce.com/catalog/inpages/mglopvdo.php

I didn't have time to pop the top cowl off last weekend so I plan to do that Friday morning. If the connection looks good I'll just drive down to ACS and buy a new one, and hope for the best!

Update: I disconnected the wire, looked at it, wiped it off (it didn't look dirty or corroded), and reconnected it. I also put a wrench on the sender and tightened it about 1/8 turn (or less) to at least shift the ground connection. Seems to be working normally now. I now feel confident that at least it is not an actual high pressure, but something in the connection(s) or sender. If it happens again I'll probably just crimp a new connector and throw a new sender on first thing.

One more question- Any one else have their indicated oil pressure drop to zero at shutdown, then after sitting a few days show some pressure (say, 5-15 psi) upon turning power on (prior to startup)?

Yes, Jim, I noticed that with my oil pressure sender and replaced it. That took care of it. I now noticed the fuel pressure is doing the same thing. Shows about 9 lbs. after a few days. If I turn on the fuel pump and then turn it off and open the purge valve to eliminate any pressure in the system, it goes back to zero. So, I may have to replace the fuel sender, too.

Vic

Thanks again Vic!

Jim Percy said:

question- Any one else have their indicated oil pressure drop to zero at shutdown, then after sitting a few days show some pressure (say, 5-15 psi) upon turning power on (prior to startup)?

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This sounds like something that might be caused by a ground loop (or "inny-outy loop", as Elippse might say ;-) ). Check that all the components of the indicator--gauge, sender, etc--are grounded to the same point in the airplane. Just turning the power on might cause a different potential at different ground points, causing what you're seeing. -Kent

Jim,

Sounds to me like you have an intermittent fault in the electrical connection - either in the signal or return ground. Measure the resistance between the transducer body and the EIS common ground point. Also measure between the terminal lug and the pin on the EIS connector. Both should be near zero ohm - lets say <0.5ohm.

With an open circuit on the EIS Oil Pressure input the indicated pressure is 99psi - any additional resistance in the signal path will cause the reading to increase just like you have seen.

The VDO transducers are German made - usually pretty reliable. If you need a replacement - Jegs have them on their website as well.

Consider testing the transducer with air pressure. For comparison my own VDO 360-004 transducer measured approx (uncalibrated reference gauge):

0 psi 7.6 ohm
10 psi 27 ohm
20 psi 44 ohm
30 psi 55 ohm
40 psi 68 ohm
50 psi 80 ohm
60 psi 92 ohm
70 psi 103 ohm
80 psi 113 ohm
85 psi 123 ohm - that is where I ran out of air pressure.

The transducer is good to 150psi.

HTH,
Doug Gray