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N131RV

Well Known Member
Bad day at T20 (Vans Guage to blame). All good now

Hey all. Got to report this.

Friday, on my way to work (Elmendorf to Houston) I'm cruising along at 9500, smooth as silk, when I notice my oil pressure drop from solid in the green (70+) to in the yellow (45).

Punching the GPS I see I am 1.7 miles from T20 (Gonzales) and elect to land there to check it out. I dialed back the power and down we go.

Safe landing, now the fun begins. Check the oil, I have 6 quarts (about what I left with). Pull the cowl and look for leaks, bad lines etc. Nothing.

Fortunately, there were some helpful folks there who let me borrow some tools. Out comes the dipstick, in goes the magnet. No metal particles on magnet. What next?

Off comes the filter and out comes the cutter (thanks to my great friend Bob who flew me in a new filter and a case of oil THANKS BOB!).

No particles in the filter. Finally after every conceivable check we can make, I elect to ferry the plane back to Zeuhl (15 minutes), since I am showing over 40lbs and my low oil pressure light had not come on.

Back at Zeuhl, more head scratching and discussin'. We put on a mechanical guage and sure enough, it reads between 15 and 20 pounds higher than the Vans guage. Vans guage had "failed' in flight, in the worst way possible.

While poking around under the cowl, I see a blue stain (UH OH). It's on some wires directly below the fuel sender. Yup, the sender is leaking (it and the oil pressure sender are mounted on the firewall using the Vans manifold). The sender is leaking around it's edge. This is the second vans fuel pressure sender I have installed. The first one was DOA and this one was put in service in March.

So score one for Vans. I get to waste two full days (and miss a day of work) because their guage "decides" to read low in flight. Verified by shorting guage lead to ground, the guage does not have full travel anymore. Verified by hooking up compressed air to sending unit and reading output (between 26 and 20 lbs difference). Verfied by hooking up my own mechanical guage to same air supply.

Plus, the FP sensor fails and drips fuel into the engine area after less than 150 hours in service.

Just FYI, folks. Check that FP sender every time you take off the cowl.

In the future, I don't think any vans guages will make their way into my panel. :)
 
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Joe, Sorry to hear about your trouble. Great write up, though...it really got me to thinking about what I should do in the same situation with my RV.

Some of the questions I have are:
- Is it common practice to immediately land with "low but steady" oil pressure?
- For a low oil pressure reading, what items should be checked in the air and on the ground?
- If there are no easy to spot problems (oil leaks, or low oil level) should you be able to continue your flight?

I recently owned a PulsarXP that had a fluctuating oil pressure indication a couple years back. It never went to the bottom of the limit (~20 psi) which would have triggered the red flashing warning light on my EIS - it actually stayed well above the bottom, but wasn't where it should have been. I continued the flight to my destination. After checking for obvious problems and not finding any, I chalked it up to a bad sender and flew home.

I guess what I'd like to know is if there is a more definitive list of go/no-go type items that require immediate grounding. Low oil pressure would certainly raise a flag with me, but thinking about it now it seems a little ambiguous if it's "just low" and not in the red.
 
Judgment call

lostpilot28 said:
I guess what I'd like to know is if there is a more definitive list of go/no-go type items that require immediate grounding. Low oil pressure would certainly raise a flag with me, but thinking about it now it seems a little ambiguous if it's "just low" and not in the red.
Click to expand...

It is a judgment call when it is "kinda low" or "less than normal." Redundancy is a big help here. Many of us with electronic engine instruments opt for a mechanical backup. This can be another gauge or a warning light as Joe had. If you could find the sender, it might be good to have a warning light that comes on before the usual 5 or so lbs. A "top of the yellow" light indication would confirm a failing gauge. Just a thought. There are other ways to cross check a low oil pressure indication. Is the temperature steady? If you have a constant speed prop, is the RPM holding and will it cycle?


John Clark
RV8 N18U "Sunshine"
KSBA
 
Low pressure procedures

lostpilot28 said:
Joe, Sorry to hear about your trouble. Great write up, though...it really got me to thinking about what I should do in the same situation with my RV.

Some of the questions I have are:
- Is it common practice to immediately land with "low but steady" oil pressure?
Click to expand...
If if had not dropped solidly into the yellow, I probably would have continued on while keeping an eye on it. But, it's a personal decision. I have flown with OP at the bottom of the green (nervously). This usually happens during a long, hard climb where I get the oil really hot (230+). I don't do that anymore if I can help it. :)
- For a low oil pressure reading, what items should be checked in the air and on the ground?
Click to expand...
I checked my oil temperature (steady, but a bit high). I could have cycled the prop. I also looked at my low oil pressure warning light as well.

- If there are no easy to spot problems (oil leaks, or low oil level) should you be able to continue your flight?
Click to expand...

If it is really low, (below redline) land immediately and do not fly the airplane until the cause is known and repaired. You are most likely about to experience a catastrophic engine failure. Of all the things that could be wrong, ONLY a bad gauge is remotely benign. You could have any number of VERY BAD THINGS going on in your engine and they all lead to a sudden stoppage:
  • Spun or worn main or rod bearings,
  • bad oil pump (rare),
  • spalled cam or lifters,
  • clogged oil pickup,
  • stopped up oil passage, etc.
  • the list goes on (and they are all bad)

If it is in the yellow, then it becomes a decision process. I made the decision not to risk my engine (and life) with 40+ lbs indicated (mid yellow).

From what I can gather, a fluctuating oil pressure is a very bad sign , usually indicating a bad bearing.

I will be installing some kind of backup oil pressure guage/sensor. Of all the things you don't want to lose, the oil pressure reading would top my list.
 
lostpilot28 said:
...I guess what I'd like to know is if there is a more definitive list of go/no-go type items that require immediate grounding. Low oil pressure would certainly raise a flag with me, but thinking about it now it seems a little ambiguous if it's "just low" and not in the red.
Click to expand...

John Clark said:
It is a judgment call when it is "kinda low" or "less than normal."
Click to expand...

While it is a judgement call, I think a low oil pressure situation (real or falsely indicated) is cause for an immediate landing. As we all know, the big fan won't keep turning if oil pressure drops too low, and it's just as easy to diagnose the problem on the ground as it is in the air. An unplanned diversion for an hour or so is much better than a forced landing.


By the way, Doug, the multi-quote function is great!
 
N131RV said:
  • Spun or worn main or rod bearings,
  • bad oil pump (rare),
  • spalled cam or lifters,
  • clogged oil pickup,
  • stopped up oil passage, etc.
  • the list goes on (and they are all bad)
Click to expand...

Thanks to all that replied to my question. Joe, the items you listed above would certainly get my attention, but wouldn't all of those cause a big spike in oil pressure? My guess is that you would have abnormally high OP until a seal blew out, then you would have really low pressure. For really high or really low indications, I agree that landing ASAP is key...it's the gray-area that I'm not so sure about. Where is the threshold between "keep flying to destination" and "get on the ground now"?
 
Well, I know it is frustrating, but I think Vans would make good on faulty gauges, and he would now know there is a problem and would procede to fix the problem.
 
Low oil pressure causes

lostpilot28 said:
Thanks to all that replied to my question. Joe, the items you listed above would certainly get my attention, but wouldn't all of those cause a big spike in oil pressure? My guess is that you would have abnormally high OP until a seal blew out, then you would have really low pressure. For really high or really low indications, I agree that landing ASAP is key...it's the gray-area that I'm not so sure about. Where is the threshold between "keep flying to destination" and "get on the ground now"?
Click to expand...

No, those items would almost certainly exhibit low oil pressure.

Some explanations:

  • worn or spun main bearing. You've lost your containment and oil will flow freely out of the bearing, lowering your overall reading. Meanwhile the bearing is shedding metal like crazy. Some of these particles will migrate to your pickup and may cover it, lowering pressure even further.
  • spalled cam or lifters, metal gets into your system, damaging the main bearings (see item 1) and also causing flow problems at the intake.
  • bad oil pump will not produce adequate pressure.
  • clogged oil pickup: starves oil pump. Pump cannot maintain adequate pressure.
  • stopped up oil passage, etc: if on input side, causes low pressure. On output side, causes overheating of affected bearings or cam

In short, your oil system is the life of your engine. Low pressure is either a symptom of something gone wrong, or a precursor to something going very wrong.

YMMV, but as for me, I will err on the side of caution. For me the limit is the bottom of the green.

A VERY helpful link: http://www.sacskyranch.com/eng26.htm
They list a lot more causes of low pressure and the bad things that happen.
 
Thanks for the explanation, Joe. That makes sense. With that, I can see how it is a prudent move to get on the ground fast.
 
Don't dismiss even small abnormalities!

On the way to Osh back in '99, I noticed a drop of about two needle widths of the needle on the oil pressure gauge. Trying to rationalize this, I attributed it to the hot weather and thin oil or my imagination. That is, until I looked out the pilot's side window and noticed an extremely thin streamer of dark liquid moving slowly back over the top of the wing. Long story short, there was 2.5 quarts of oil in the engine and 5 on the bottom of the airplane when I got her on the ground. A pin hole leak had developed in my oil cooler and was spraying inside the engine compartment. If you notice anything abnormal with the oil pressure gauge, take it very, very seriously. I am considering a back-up oil pressure light or mechanical gauge for this reason. My two cents.
 
Back in the air, all good now

Just a followup, vans did ship my replacements Friday and they arrived Monday via USPS priority mail. Thanks Vans!

I installed the new FP sender and the new OP gauge and my pressures are reading normal again (about 82 on startup and 68-72 after reaching cruise).
 
Could be worse?

I appreciate you got the shaft from your bum transducer/sender and a little raw from your sender lying to you.

I'd rather a bum gauge and precautionary landing, than a real low oil pressure and doing a real urgent landing.

"Vans gauge had "failed' in flight, in the worst way possible."

What about a gauge that says all is good and it is not? :eek: :D

You did the right thing but pilot's have a great ability to be in great denial. Believe your gauges. Don't second guess, just land (as you did). I've seen guys get in all kinds of trouble by denial & disbelief of info they have, namely what the gauge says. Unless you really know the gauge is lying, believe it. A very large airliner did a dead stick landing, due to fuel starvation, in part because the crew disbelieved gauges (re: Air Trasat Flt 236). http://en.wikipedia.org/wiki/Air_Transat_Flight_236

Great tip on checking senders for leaks. Has any one had a VDO sender failure that GRT supplies with their EIS4000?
 
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