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Oil Pressure Fluctuating Wildly

T

Towline

Member
Flying home a couple of days ago, I noticed the oil pressure light flashing high on my OPT-1 from EI.

Panic slightly... then it returns to normal for a bit and then drops to low (literally zero on the readout). Then back to high (120+). Edited to say at this point I thought the only reliable thing I can maintain my concentration on is the oil temp, which remained solid thoughout.

Luckily I was 15 minutes from home so throttled back a bit and it seemed to stay in the normal range, until I powered back to land (dropped down low again).

On landing, no oil loss, no signs of leaks and as said the oil temp remained absolutely constant throughout.

I'm runnning an O-320 D1A with fixed prop and no inverted systems. Oil change about 4 hours (4 weeks) ago. I've noted that it might be worth checking the ball in the relief valve. Just wondered if anybody has had problems with these transducers that might cause such erratic readouts? I've got a licenced eng doing some troubleshooting on it.
 
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Erratic Oil Pressure

You did not state what type of transducer you are using. Assuming it is a VDO type check to ensure the ground is good. The units ground through the case so an easy way to check it is to use a hose clamp and clamp a wire to the housing and connect it to a grounding point, then go fly.
I had the same problem years ago.
 
Sounds like it may be just indication but PLEASE don?t fly it until pressure is checked with a direct reading gauge.
 
Yeah roger that. Our engineer has said the same, for me to check grounding on the transducer.
 
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Had a customer call with this very issue. We went down the same suggestions posted here, all are good. He is based a 40 min flight away so it was difficult to troubleshoot.
I suggested he add another qt of oil and the fluctuations went away. It seems under the right circumstances cavitation can occur at the oil pick up in the sump.
If nothing else it's a cheap place to start.
Cheers!
 
Oil Pressure

Minimum oil quantity for most four cylinder parallel valve Lycoming's is 2 quarts. I don't accept thee premise that adding one quart of oil would make wild oil pressure fluctuations go away, unless the oil level was down to one quart.
 
jrs14855 said:
Minimum oil quantity for most four cylinder parallel valve Lycoming's is 2 quarts. I don't accept thee premise that adding one quart of oil would make wild oil pressure fluctuations go away, unless the oil level was down to one quart.
Click to expand...

Agreed. Cavitation typically results in ongoing pressure swings more in the 25%-50% range and not a momentary, complete loss of pressure. Assuming a minimal oil level of course, though there is really nothing to create cavitation unless overfilled. Sucking in air momentarilly (which is NOT cavitation) when oil level is very low, will create this type of indication, but I also think that level is close to 1-1.5 quart.

Instrumentation is far more likely for this type of presentation, assuming a full sump. A single occurence of an immediate pressure loss with immediate reversal is just not a marker of typical oil pressure problems, other than the low oil situation mentioned above.

Larry
 
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Oil Pressure

For those who are not familiar Pitts Aircraft usually have a bolt on inverted oil system that was originally marketed by Christen Industries. Aviat now controls the former Christen products. Sometimes a new port is welded to the bottom of the sump.
Under certain conditions this system will result in a momentary loss of oil pressure. This is typically down to the 25# range and will immediately recover to normal with no additional fluctuations. This is caused by the ball in the three way valve not being seated in zero G conditions.
A separate issue is that in a sustained 90 degree left wing down bank the oil pressure will go to Zero. If the bank is to the right the oil pressure stays normal.
 
Oil pressure fluctuating, then to zero

Following a normal run up, I took off for a short flight to my home airport. After a few minutes I noticed my oil pressure dropping, then rising a bit, then dropping more. Finally it dropped to 0. Very alarmed I landed at an airport I happened to be near. During all this there were no other abnormalities, sounds or indications. After landing, I suspected the pressure sender or wiring to the EFIS. I removed the VDO sender, banged on it a little, wiggled wires, then reinstalled the VDO. I restarted the engine and oil pressure came up perfectly normal. I reasoned this was a sensor problem, not a true oil pressure loss. I took off again, with only about 15 mins remaining on my return leg home. Then, a few minutes after taking off, the same thing happened again, fluctuations followed by 0 oil pressure indication. I flew on home. Again no other abnormality. I haven?t yet determined the problem. I have ordered a mechanical oil pressure gauge to see what?s going on.

This occurred on a very hot day, about 93F. Yet the oil temp was indicating 185F , not really that hot, assuming a correct instrument. I?ve seen hotter with no adverse effects. Is there any scenario where high oil temp could cause this kind of problem? Any other ideas ?
 
No help here other than to confirm that an imperfect connection with modern senders can indeed show "wild fluctuations down to zero."

My #3 EGT and fuel pressure readings are currently both doing this intermittantly. On my Dynon, when the signal goes completely away (contact lost) an "x" appears, confirming the loose wire diagnosis. I have a header tank for an updraft carburator; even if my fuel pressure drops to zero in real life I should be fine - but do plan on tightening everything up next time I remove the cowling.
 
EI connectors are notorious for acting in this manner. The voltage requirement for the gauge is so small that the least bit of oil and or corrosion on the connector will affect it. The wide range of the gauge reading is a classic sign of this.

If you are still using the spade style connectors that EI used to supply with their instruments they have a new barrel connector that uses a set screw to hold the wires together which seems to be an improvement.
 
Aviaman said:
I removed the VDO sender, banged on it a little, wiggled wires, then reinstalled the VDO.
Click to expand...

Personally, I think those things SUCK. Swapped out for Kavlicos and never looked back over 500 hours ago. Not a single issue with them since the change.
 
Oil pressure fluctuating wildly

Can you give me a Kalvico oil pressure sender part number? The website has a lot of stuff there.

Thanks,
John
 
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