Oil pressure dropped to -zero- today...

[dholly]

...yep, that'll get your attention right quick!

Well, after an anxious eye on the other gauges and a quick but uneventful return to the airstrip, I presume my original VDO oil pressure sender has given up the ghost at ~175 hrs. Short of sticking it in a thermos of hot coffee, not sure how I would go about testing that? I searched a few sites and found VDO sender failures often began with an erratic gauge with many taking some time to fail completely, but I didn't find any comments about a sender working fine one second then dead at 0psi the next.

Curious if anyone else here has experienced a similar failure?

[Av8r3400]

Doug, is it safe to assume that you chased the leads from gage to sender?

I've actually had that happen on several gages on my plane and it wound up being a loose connections.

Right now my egt is giving me fits. (Luckily it is mostly unnecessary on a 912.)

[Dorsal]

I have had mine go over pressure when a lead broke but not to zero. You do mean oil pressure right? the thermos of hot coffee threw me off
If it is in the wires I believe they would have to short to give this result (might check wear points).

[HighWing]

It took over a year for the FAA to call me with the determination that it was indeed a low oil pressure situation that prompted our emergency landing in a very unforgiving location.

Not wanting the uncertainty to happen again, I first mounted the oil pressure sender remotely on the firewall to eliminate the vibration issues. Then I added an idiot light on a manifold so I had a back-up indicator. Then not wanting to wonder if it was a power issue, I found a pressure switch that is double pole so the green LED along with the gauge indicates all is good. If the gauge goes south and the green light remains lit, I know I have pressure. If the gauge goes south and I get a flashing read, I have real pressure issues.

[n85ae]

Nice and tidy install there Lowell, like that you use the waxed lacing tape as well.

Regards,
Jeff

[akarmy]

I too had my sender fail, I mounted a new sender on the firewall with a nice kit that John sells. No problems since.

[Russell320]

I am surprised more pilots don't have some sort of alternate oil pressure indicating like you have Lowell. I also have the second source of a capillary mechanical gauge that most people in aviation don't advocate. I inspect it regularly and feel the benefit far outweighs the potential danger. The VDO senders are great when they work, but a huge worry when they quit. My mechanical gauge also works very well without electrical power.

[dholly]

I have the pressure sender and temp wire leads from the engine to firewall in black flexible, corrugated tubing for chaff and temp protection. I did a pretty good look see and found nothing abnormal, which is why I felt the sender failed. I read a comment somewhere that if you disconnect the sender leads and the gauge then reads 50psi it is in all probability a sender failure, that info supposedly gained form a call to the manufacturer. Haven't had time to try that yet though.

Lowell, thank you for sharing, I really like your solution. Having that certainty would give me a warm fuzzy now too and I'm giving it serious consideration. For the sake of discussion I am pasting a post found on the Just forums:

The old VDO unit is mechanical, there are levers and springs that move in response to oil pressure changes. It is susceptible vibration and shock. It only costs $40.

The new and improved Honeywell sensor uses a pressure transducer, which is much less susceptible to vibration. It costs $270. The remote mounting kit is ~$100.

In the RV12, my approach was to buy two of the inexpensive VDO sensors, one installed directly to the engine and the other for a spare. The spare is fast and easy to install in the field. My rational is that if the oil pressure sensor fails, it doesn't matter which kind it is, the engine will continue to run and I will be safe, maybe a little edgy for the rest of the flight. If the oil pressurization system fails, I'm in trouble no matter what kind of sensor I'm using.

Hehe, yes Finn oil pressure not temp. The coffee comment was tongue-in-cheek as I saw that quote on another site while researching the problem (rec flying maybe?).

[Jerrytex]

When I was hooking up a VDO sender to my MGL E-1, the owner of MGL (cant think of his name right now) helped me troubleshoot a VDO sender with an OHM meter. Turns out it was a bad sender right out of the box. Might give MGL a call or maybe you can find what the ohms are supposed to be for a paticular pressure and use an air hose to supply regulated pressure.

On a side note: I too thought the same thing about the electronic oil pressure senders. That would be a scary situation to have questionable or no oil pressure and have to make an emergency landing in a perfectly airworthy plane all because of a bad sender. I added a mechanical oil pressure gauge so if the MGL E-1 indicates an oil pressure problem, I can compare it to the mechanical one. I have also heard the horror stories about bringing oil into the cockpit too but I thought it was lesser of two evils as well. Especially since my head is about 6 inches away from 13 gallons of Avgas.

[cap01]

lowell , great idea for the pressure switch . wondering what kind of switch you used and where you got it ? sounds like another next winter project . got to plan ahead