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Fluctuating Oil Pressure Indication?

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darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sun Apr 05, 2009 9:15 am Post subject: Fluctuating Oil Pressure Indication?

Last time I went flying, about 10 minutes into the flight, my oil pressure indication went to 12 psi then to 45 psi then back to 15 psi and it continued like this until I got back on the ground about 10 minutes later.  When I shut down, my EIS still indicated oil pressure without the engine running.  I had just purged the oil system per the Rotax SB so there was not any air in the system.  I have purged it again since and I am still getting the wildly fluctuating pressure indication.  The engine only has 38 hours on it which seems a bit early for failure. 



The pressure eventually went to 0 but shouldn't it be 0 anytime the engine is not running even if the engine is warm?  Is my pressure sender bad?  I know they have a tendency to go bad on the Rotax 912 series due to engine vibration.  But is this a typical symptom of a bad sender or do they just quit indicating completely?



Lastly, does one have to spend the outrageous amount of $250 for a new "Rotax" VDO sender or will others work?  If so, where can I get one of the less expensive ones?  I am sick of not being able to fly on days like today and need to get this figured out.  So any help or experience you may have will be appreciated.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

akflyer

Joined: 07 May 2007
Posts: 574
Location: Soldotna AK

Posted: Sun Apr 05, 2009 10:47 am Post subject: Re: Fluctuating Oil Pressure Indication?

couldn't you jump a tee in the run and put a good ole mechanical oil pressure gage in there too for back up?  That would for sure tell you what the scoop is for about 25 bucks at any auto parts store.  You would not have to punch a hole in the dash for it, just set it on the seat or use a clamp to hold it at the edge of the dash just to give you a warm fuzzy that the high $ sender is bad.

_________________
DO NOT ARCHIVE
Leonard Perry aka SNAKE
Soldotna AK
Avid "C" / Mk IV
582 (147 hrs and counting on the rebuild)
IVO IFA
Full Lotus 1450
#1 snake oil salesman since 1-22-2009

I would rather die trying to live, than to live trying not to die....

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sun Apr 05, 2009 11:27 am Post subject: Re: Fluctuating Oil Pressure Indication?

 	  akflyer wrote: 	
		  couldn't you jump a tee in the run and put a good ole mechanical oil pressure gage in there too for back up? 	




Yes, I thought about this and will probably end up doing it or at least trying it to verify if the sender is bad.  I did just read that the VDO senders show signs of failure by rapidly fluctuating pressure indications.  Based on this, I think it is safe to assume that the sensor is going bad.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

akflyer

Joined: 07 May 2007
Posts: 574
Location: Soldotna AK

Posted: Sun Apr 05, 2009 11:55 am Post subject: Re: Fluctuating Oil Pressure Indication?

It may be a good idea to install the mechanical anyway.  I wonder (out loud) if anyone has ever set a perfectly good plane down.... and balled it up, due to a faulty sender.

Vic Baker

Joined: 11 Jan 2006
Posts: 71
Location: Carson City, Nevada

Posted: Sun Apr 05, 2009 12:47 pm Post subject: Fluctuating Oil Pressure Indication?

My oil pressure sender failed after 30 hours total time on engine. 

Indicating high (red line).  Replaced it with "non aviation" unit from 

Lockwood.  $40     Telcon with Lockwood,  not unusual for this to happen.



Note:  Lockwood also recommended remove, clean threads, try again.  Did not 

help.

Also recommended  install mechanical gauge.  Have not done that.

Vic Baker

S7 912S Warp

Phase 1 flight testing

Carson City, Nv

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_________________
Vic Baker
Series 7
Carson City, Nevada

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Apr 05, 2009 1:00 pm Post subject: Re: Fluctuating Oil Pressure Indication?

Hi Darin,



Very first thing is get to the back of the panel and use a wire and touch the gauge ground to a know good ground. This is my first guess for what you describe, bad ground. If this is not it then my second guess is the sending unit. If the grounding doesn't fix it then you need to go to the hardware store and pick up a gauge from 0-100 psi and some 1/8" copper tubing. The oil pressure fitting threads is 1/8" NPT. Get a 1/8" NPT to a compression to come out of the oil sender port. Then come out with the tubing about 18" and put a tee in the line and continue the copper tube run until it gets well inside the cockpit. Put your oil sender gauge in the tee. Put the pressure gauge on the end of the line. When you run the engine you will be able to compare mechanical pressure with the electronic pressure. When you start the engine partially unscrew the pressure gauge until the oil starts to weep out the threads and then tighten the gauge. This will allow all the air to be purged out of the test line. These are VDO gauges and the VDO guage with the cadmium anti vibration ring cost up to $250. You can get the identical VDO gauge without the cadmium ring for $39.95. These seem to last just as long and I can replace this one a lot of times for just one of the others. Get the VDO gauge from Lockwood Aviation. Call me if you have any questions.  520-574-1080



Both of these things are very easy to do.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sun Apr 05, 2009 1:58 pm Post subject: Re: Fluctuating Oil Pressure Indication?

Thanks for the input guys.  As Roger recommended, I have checked the grounding and all is good.  I am going to get a new sender and found them at Jegs. com for $25.99.  As Roger said, they don't have the vibration ring around them but I plan to mount the sender remotely this time.  Thanks again for the info.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Apr 05, 2009 6:11 pm Post subject: Fluctuating Oil Pressure Indication?

Thinking out loud here but that may have been what happened to Lowell.



Noel



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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sun Apr 05, 2009 7:23 pm Post subject: Re: Fluctuating Oil Pressure Indication?

Noel, I was thinking the same thing when it happened.  I thought that if I really was losing oil pressure it would be steadily decreasing to 0 but it kept jumping all over the place so I was pretty sure this wasn't an actual oil pressure problem but rather an indication problem.  I did have the Brigham City airport about 4 miles ahead but opted to turn back towards Ogden - my home base.  I have located another sender (summitracing.com) and ordered the hose and fittings to go to a remote setup so I can get rid of the vibration issues common to senders mounted directly on the engine.  Got the sender, hose, insulation sleeve and fittings for under $100 which is much better than the $250 I thought I was going to spend.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

lcfitt(at)sbcglobal.net
Guest

Posted: Sun Apr 05, 2009 8:02 pm Post subject: Fluctuating Oil Pressure Indication?

Noel,



For a long time, I wondered if it was the pressure sender or frankly, if I 

had mistaken the temp gauge as the pressure gauge as the temp senders had 

failed fairly regularly.  It wasn't until several months later that I got a 

call from the FAA and they wanted to see me at the FSDO.  It was then that 

they showed me the black glob that they found in the oil tank with the 

string that had melted off the glob that was sucked into the pick up tube. 

I don't know if it was a relief to find that there was indeed a correct 

reading on the oil pressure gauge, because I then had to think how something 

like that could have been introduced into the oil system - most likely by 

me.  I still haven't figured that one out.



Lowell



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Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Mon Apr 06, 2009 4:17 am Post subject: Fluctuating Oil Pressure Indication?

It might be better to run a hose with a fitting off of the engine to read the pressure if you elect that method. As I recall, a copper tube can become brittle and break under vibration. If you do decide to use the copper a suggestion would be to put a coil in it to help absorb the vibration. That is the method the "old timers" always told me to do it.

  I believe John McBean mentioned in one of his posts, that he has a remote oil pressure sensor kit available. I don't know anything about it but I have been meaning to contact him about this as my oil pressure sensor has failed once and I am sure it will again.

                                              Dick Maddux

                                              Fox 4-1200

                                              912 UL

                                              Pensacola,Fl

 Feeling the pinch at the grocery store?  Make dinner for $10 or less.

  [quote][b]

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Mon Apr 06, 2009 5:57 am Post subject: Fluctuating Oil Pressure Indication?

Don't forget to cover the line inside the cockpit in case it holes.  You

won't want hot oil spraying over your legs!



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Mon Apr 06, 2009 6:11 am Post subject: Fluctuating Oil Pressure Indication?

I had a Rover TC 2000 many years ago.  After finally getting it fixed a and

running like a Swiss watch one day it suddenly seized just after starting.

When I took the head off I found little pieces of carbon hard steel imbedded

into all four of the cylinder heads and of course all my valves looked like

pretzels.  I took a few of the pieces, which I had identified as pieces of a

compression ring, to all the auto dealerships and finally to a heavy

equipment dealer.  It turned out the pieces were from the main compression

ring of a D 9 Caterpillar tractor.  The engine being side draft with two

carbs couldn't have ingested the particles so the only way they could have

gotten into my engine was they had to be intentionally put in there through

the spark plug holes.  I still don't know who may have done this.



In your case I was thinking some of the oil bottles have the little plastic

retainer rings which I have seen fall off some bottles.  This could have

happened to your engine if the glob you mentioned was plastic or it could

have been part of a rag inserted in a hose to keep bits and pieces out.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Mon Apr 06, 2009 6:19 am Post subject: Re: Fluctuating Oil Pressure Indication?

I don't mean for him the go fly with this setup. Everything you need to do can be done on the ground and you use copper or stainless because it is less likely to split over plastic lines and that is why you use a very small I.D. line to reduce any volume issue in case of a problem, plus there is no need for big lines when testing pressure only. Copper is just easier and cheaper to work with. You should have no leaks or rupture issues with only the Rotax oil pressure of 35-60 psi from the engine. You only need to run the engine for a couple of minutes to diagnose your problem. The problem is there or it isn't, no long run times needed. This is a very simple and telling procedure. [/u]

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Last edited by Roger Lee on Mon Apr 06, 2009 7:50 am; edited 1 time in total

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Mon Apr 06, 2009 7:20 am Post subject: Re: Fluctuating Oil Pressure Indication?

I am making a remote setup using -4 Aeroquip Socketless hose and fittings and will mount my sender to the firewall.  I am going to install a tee at the sender so I can connect a simple analog gage and compare the two readings, I can then cap the unused side of the tee and be done with it.  This will allow for future diagnosis if needed.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

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