guage says NO OIL PRESSURE but I know it is a liar

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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ussyorktown
Posts: 423
Joined: Sun Apr 01, 2012 9:19 pm

guage says NO OIL PRESSURE but I know it is a liar

Post by ussyorktown »

I started up my Flight Design CTSW and it said on the anologue guage ZERO for oil pressure.
I turned her off and took a look.
What happened is that my dip stick didn't go all the way in and when I turned the cap back on it didnn't cover the entire well. So the oil pressure must have said zero.

So, I put the cap back on the oil correctly.
BUT, the guage still says zero oil pressure.
i took her out for a spin and the CHP and oil temp were normal.

How do I get the pressure guage to tell me the truth?
3Dreaming
Posts: 3107
Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Post by 3Dreaming »

It could be a bad wire connection, the sending unit, or the gage. I would check things in that order.
ussyorktown
Posts: 423
Joined: Sun Apr 01, 2012 9:19 pm

Thanks

Post by ussyorktown »

I've been told that by Flight Design in Connecticut. But can't locate where the sending unit, wires, etc. are all located under the cowl. Could you give me a vector to it?
Jim Stewart
Posts: 467
Joined: Thu Oct 12, 2006 6:49 pm

Post by Jim Stewart »

Here you go:

http://grumpyoldgeek.com/images/Rotax912S_oil.jpg

I've had both the oil pressure and coolant temp show flaky readings. All times they were fixed by cleaning and tightening the electrical connections.
Last edited by Jim Stewart on Wed Apr 04, 2012 7:24 pm, edited 1 time in total.
roger lee
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Joined: Tue Dec 08, 2009 11:47 am
Location: Tucson, Az. Ryan Airfield (KRYN)

Oil pressure readings

Post by roger lee »

There are signs of what the problem is.
If the gauge pegs out on the high side then it has no ground. If it goes way down when you advance the throttle and then back up again when you go to idle it is an incomplete ground and the resistance change is the causeof the gauge change. If it goes to zero it is usually a dead sender.
Go to: http://www.egauges.com/vdo_send.asp?Sender=150PSI_10Bar
90% of the time it's the sender.

If it is zero it never hurts to put a mechanical gauge in line to double check, but Rotax typically doesn't have zero oil pressure issues.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
howardnmn
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Joined: Thu Dec 30, 2010 4:20 pm
Location: san francisco bay area (mill valley)

Post by howardnmn »

i have a mechanical fuel pressure gage on my 912uls which has been problematic for a long time. i discconected the fuel line that goes to the gage and found if filled with gunge...waxy like high viscosity crap. i let it drip out into an oil pan. cleaned the gage and it now works fine. problem is the line going to the gage (or pressure transducer) is a dead end with no circulation. periodic draining of this line when gage is sluggish is simplist solution.
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roger lee
Posts: 807
Joined: Tue Dec 08, 2009 11:47 am
Location: Tucson, Az. Ryan Airfield (KRYN)

fuel pressure line

Post by roger lee »

Mounting the fuel pressure sender off the engine is the right thing to do.

If you mount it lower than most of the engine and use 91 oct. then each annual just unscrew it and open the fuel shut off for 2-4 seconds and let it flush it out. The fuel in that line sits for a year and just cooks and it will start to go bad just like fuel did in the old days. No fresh fuel will exchange with it in that position. 100LL isn't as susceptible, but 100LL does too many other bad things to an engine.

It's all about placement.

The best thing to do is mount the fuel pressure sender slightly higher than the engine. That way after you shut down and things drain and settle while the engine sits the fuel drains away and out of the line. When you start the fresh fuel charges the line. I have done it this way now for 5 years with my fuel pressure sender slightly above the engine and I have never had a bad fuel issue. For the guys that have the mountings low I have seen many issues, but draining will always take care of it. I also clean out the small orrfice in the sender itself with some carb cleaning spray. Works very well and won't hurt the sender.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
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deltafox
Posts: 306
Joined: Tue Apr 06, 2010 2:21 pm

Post by deltafox »

My fuel pressure gauge was giving me a problem in my Dynon/PiperSport. I disconnected the line during an oil change and found the same kind of gunk described above. Now I clean it out with each oil change. Maybe ethanol?
Dave
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