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hgmckay
Joined: 23 May 2006
Posts: 397
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 Posted: Mon Apr 04, 2011 8:55 am Post subject: Drop in Oil Pressure |
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My 912 UL oil pressure normally runs right at 4 bar (58.8 psi). Recently I have noticed the pressure has dropped to 3 bar (44.1 psi), a drop of 25%. Don’t understand why? The only thing different in my operation is two weeks ago I had to make a three hour flight to Macon, GA and then returned to N92. While in Macon I put 10 gallons of 100LL in my main tank (the only fuel available). This is the first time I have had to use 100LL in the 430 hours I have flown the plane. I noticed the drop in oil pressure a few days after that flight. Any reasonable explanation for this drop in pressure?
Hugh G. McKay III, P.E.
Senior Consultant
Worldwide Engineering Inc.
4090 North NC Hwy. 16
Denver, NC 28037
Ph. 704-661-8271
Fax 704-483-5466
email hgmckay(at)bellsouth.net
http://www.wwegeo.com
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BARRY CHECK 6
Joined: 15 Mar 2011
Posts: 738
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| Posted: Mon Apr 04, 2011 9:53 am Post subject: Drop in Oil Pressure |
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Hugh:
With the information given there is NO reason why you should see a pressure drop from changing to AvGas for a few hours.
Do you have EGT & CHT gages? If so what were their readings?
You may see a drop in EGT due to the higher octane, but that would be very slight. CHT... May also have come down 5 degrees F.
Are there any LEAKS?
A long flight will have steady high temps and steady vibration - Putting this together may just develop a small leak.
Are there any CLOGS (dirty oil)?
Dirty oil looses viscosity and even more at temps. A loss here will show as a loss in oil pressure.
How HOT is your oil?
As oil increases in temperature BEYOND normal the oil thins. This is shown as a DECREASE in oil pressure and an INCREASE in oil temperature.
Being that AvGas has a high lead content and engines that use it regularly have shown an increase in blow-by. This blow-by surely will weaken the qualities of the oil and can show early signs as a DECREASE in oil pressure and an INCREASE in oil temperature.
OK - That's all for now... You will have to give more information and see what time shows.
Barry
On Mon, Apr 4, 2011 at 9:02 AM, Hugh McKay <hgmckay(at)bellsouth.net (hgmckay(at)bellsouth.net)> wrote:
[quote] My 912 UL oil pressure normally runs right at 4 bar (58.8 psi). Recently I have noticed the pressure has dropped to 3 bar (44.1 psi), a drop of 25%. Don’t understand why? The only thing different in my operation is two weeks ago I had to make a three hour flight to Macon, GA and then returned to N92. While in Macon I put 10 gallons of 100LL in my main tank (the only fuel available). This is the first time I have had to use 100LL in the 430 hours I have flown the plane. I noticed the drop in oil pressure a few days after that flight. Any reasonable explanation for this drop in pressure?
Hugh G. McKay III, P.E.
Senior Consultant
Worldwide Engineering Inc.
4090 North NC Hwy. 16
Denver, NC 28037
Ph. [url=tel:704-661-8271]704-661-8271[/url]
Fax [url=tel:704-483-5466]704-483-5466[/url]
email hgmckay(at)bellsouth.net (hgmckay(at)bellsouth.net)
http://www.wwegeo.com
[b]
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Mon Apr 04, 2011 5:12 pm Post subject: Re: Drop in Oil Pressure |
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Hi Hugh,
If the pressure is steady then it shouldn't be a ground or wiring issue. The oil pressure senders are notorious for going out and they do many times go out slowly by dropping pressure. The sender is a rheostat type so vibration or heat over time can cause them to go bad. I would be willing to bet you don't have a real oil problem, but just a bad reading. You can pick up a sender from Lockwood for around $36 and try it. The other thing may help is put in the new Rotax oil pressure regulator cone and taller plug screw if you haven't done so already.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Tue Apr 05, 2011 4:34 am Post subject: Drop in Oil Pressure |
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Hugh,
I suspect,as Roger does,that you have a bad oil pressure sensor.
A while back, I was reading low oil pressure on my gage in my aircraft so I decided to check it with my air compressor gage.(using a rubber tipped air nozzle on the air hose) I removed the sensor ,set 60 lbs of pressure on my air compressor, applied it to the oil pressure sensor, and found that the gage in the aircraft was reading 10-15 lbs low from the compressor gage. Now I KNOW that the compressor gage is probably not that accurate but I still decided to put a new sensor in the aircraft anyway. Surprise ,it agreed with the compressor gage on testing and I was back up to 55 lbs at cruise again.
You might also be able to install a temporary oil pressure gage to check for accuracy of your existing system.
You also might,have carbon or some other type of grit holding the ball open on your oil pressure regulating system.(easy to check) I kind of of doubt it but maybe. Installing the new cone system,as Roger mentioned, might help also. Just some ideas.
Dick Maddux
912UL
Milton,Fl
[quote][b]
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moosepileit
Joined: 10 Dec 2007
Posts: 26
Location: USA
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| Posted: Tue Apr 05, 2011 2:48 pm Post subject: Re: Drop in Oil Pressure |
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Agreed on previous advice. $15 for a local auto parts direct reading kit. Install and run up. Hopefully, big smile if not the engine's issue. You'll probably find it is the sender, not the engine. 750 TT, 58psi before, 58psi after the new sender.
I had a high reading then low reading and erratic sender- 100+ psi high and 20 psi low. Once removed, the old sender bench tested fine w/ steady air pressure and no vibration on an ohm meter.
Install the new sender, good for a few years or a few hundred hours.
Should not be a bad ground or loose connection if it gives a steady reading as installed currently, but always good to check. Some places you will find say use no thread sealant to avoid case grounding issues. Other say to use a sealant. I used white #59214 permatex thread seal, YMMV.
Found these ohm values today on the net:
Rotax 912 UL running the Standard VDO Oil Pressure Sender 360-004, or 29/12 stamping on the hex along w/ a date of mfg of in 2 digit month/2 digit year.
VDO 0 - 10 bar oil pressure sensor, Bar psi Resistance (Ohm's)
BAR=PSI= OHMs on sender
0 = 0 = 7.2
0.5 = 7 = 18.2
1 = 14.5 = 28.2
1.5 = 21.75 = 39.2
2 = 29 = 49.2
3 = 43.5 = 68.2
4 = 58 = 87.2
5 = 72.5 = 104.2
6 = 87 = 121.2
7 = 101.5 = 137.2
8 = 116 = 153.2
8.5 = 123 = 160.2
9 = 130.5 = 167.2
10 = 145 = 181.2
Good luck! I was worried about high oil pressure possible meaning a bad bearing, then the low pressure meaning lost bearing. That was no fun watching the oil temp like a hawk while returning to land.
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Tue Apr 05, 2011 3:16 pm Post subject: Re: Drop in Oil Pressure |
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Making an oil pressure gauge setup to mechanically check oil pressure while checking the electric oil pressure. (This post isn't for you if you already have a mechanical oil pressure setup to your instrument panel)
If you have an electronic oil pressure gauge in the cockpit and you think you pressure is too low and don't no if it really is low (rare) or if it might be the sneder or ground then here is an easy to set up check.
Hop on down to the hardware store. Buy 5' of 1/16 copper tubing. buy 4 1/8-27 NPT to compression copper fittings. Buy a dial gauge that reads up to 100 psi. Buy a 1/8 tee fitting.
Take out the oil pressure sender (threads are 1/8-27 NPT). Put one of the compression fitting on the end of the cooper tube. Screw that into where you took the oil pressure sender out. Cut the tubing about 18" out from there and install the tee with one side of the copper tube going in and the other going out. (two compression fittings here). Now screw in your oil pressure sending unit on the top of the tee. It will be grounded through the copper tubing. On the end of the copper tube use another compression fitting and screw on you mechanical gauge. Don't tighten it. Start the engine and allow any air to come out up by the gauge and when you see a drop or two of oil you know the copper line is full and the air is out. Now tighten the gauge. Run your engine up and compare the electric signal oil pressure with the mechanical one. This is about a $20 diagnostic tool.
See playing with Tinker Toys as a kid does help later in life. So give them back to your kids and remember when.
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Tue Apr 05, 2011 5:15 pm Post subject: Drop in Oil Pressure |
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Do you have to purge the oil system after you replace the oil pressure sensor on a 912 UL?
Hugh G. McKay III, P.E.
Senior Consultant
Worldwide Engineering Inc.
4090 North NC Hwy. 16
Denver, NC 28037
Ph. 704-661-8271
Fax 704-483-5466
email hgmckay(at)bellsouth.net
http://www.wwegeo.com
From: Catz631(at)aol.com (Catz631(at)aol.com)
Sent: Tuesday, April 05, 2011 8:24 AM
To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com)
Subject: Re: Drop in Oil Pressure
Hugh,
I suspect,as Roger does,that you have a bad oil pressure sensor.
A while back, I was reading low oil pressure on my gage in my aircraft so I decided to check it with my air compressor gage.(using a rubber tipped air nozzle on the air hose) I removed the sensor ,set 60 lbs of pressure on my air compressor, applied it to the oil pressure sensor, and found that the gage in the aircraft was reading 10-15 lbs low from the compressor gage. Now I KNOW that the compressor gage is probably not that accurate but I still decided to put a new sensor in the aircraft anyway. Surprise ,it agreed with the compressor gage on testing and I was back up to 55 lbs at cruise again.
You might also be able to install a temporary oil pressure gage to check for accuracy of your existing system.
You also might,have carbon or some other type of grit holding the ball open on your oil pressure regulating system.(easy to check) I kind of of doubt it but maybe. Installing the new cone system,as Roger mentioned, might help also. Just some ideas.
Dick Maddux
912UL
Milton,Fl
[quote]
href="http://www.matronics.com/Navigator?RotaxEngines-List">http://www.matronics.com/Navigator?RotaxEngines-List
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Tue Apr 05, 2011 6:06 pm Post subject: Re: Drop in Oil Pressure |
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Hi Hugh,
No you do not need to purge after changing the oil pressure or oil temp probe. You will only drool a little oil.
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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