Bad day at T20 (Vans Guage to blame).

[N131RV]

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.

[lostpilot28]

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.

[John Clark]

Originally Posted by lostpilot28

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.

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

[N131RV]

Originally Posted by lostpilot28

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?

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?

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?

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.

[RBD]

Originally Posted by lostpilot28

...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.

Originally Posted by John Clark

It is a judgment call when it is "kinda low" or "less than normal."

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!

[Khelmar]

Has anyone installed an oil level sensor? It seems like a logical way to get a little more information about the oil state during flight.

[lostpilot28]

Originally Posted by N131RV

• 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)

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"?

[prporter]

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.

[AlexPeterson]

This thread is deja vu, see:

http://www.vansairforce.com/communit...ad.php?t=21248

This seems to further prove the worthiness of a mechanical backup oil pressure gage.

[N131RV]

Originally Posted by lostpilot28

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"?

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.