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Peteohms
02-08-2009, 03:21 PM
Lately I have been experiencing erratic oil pressure in my 912. Upon startup I get instant oil pressure as normal. After warm up and takeoff I fly for awhile and sometimes my oil pressure dips down to 20 briefly and goes back up to 40. This may happen several times but usually not when the engine is good and hot say 200f degrees. I'm using 20W50 Honda oil. I know that's a bit thick for winter but it averages 60f degrees around here. Any ideas?

Dave S
02-08-2009, 05:21 PM
Hi Pete,

Well, I am not going to say that I know what is going on; however, I'll toss out a few ideas on chance that some might help you diagnose this deal.

First off - when faced with a screwy gauge reading - It is good to know if the gauge is lying or not. Think of it not as erratic oil pressure; but, as an erratic oil pressure indication.

Electrical gauges can lie for a number of reasons, including but not limited to: a) the sender unit is messed up, b) the wiring is defective - (loose or cracked wires, etc), c) a messed up gauge voltage regulator - if one is used, d) the gauge itself has a problem or a loose wire. A person might consider system voltage too - if an alternator is cutting in and out for one reason or another - system voltage could vary by 2 volts or so, although I don't know if this is enough to affect an electrical gauge.

Direct fluid/pressure type gauges usually either work or leak - sometimes they even work if they leak. If they have a problem - it is usually the sender, the tubing or the gauge.

It might be a good first step to be sure all electrical connections and wiring from the engine to the gauge are OK (or the plumbing if it is a fluid/pressure gauge) - at least it doesn't cost much to check.

Ideally - It would be good to have a known good pressure gauge plumbed in to compare with the panel gauge under the conditions the issue expresses itself. This way a person could know for sure if the gauge is lying; or, if you have a real oil pressure fluctuation.

Keep us up to speed on your success in figuring this out.

Sincerely,

Dave S
KF 7

Peteohms
03-09-2009, 05:44 PM
The eratic oil pressure indications seem to have gone away with an application of brake cleaner to the connections.

DesertFox4
03-09-2009, 10:27 PM
Pete,

Glad to hear you solved the oil pressure reading problem. I've had a couple oil pressure senders go bad but when they failed they indicated extremely high oil pressure readings setting off my EIS warning light.
They would go over 85 psi to maybe 100 psi readings. Maybe they are designed to indicate this way when they fail instead of low readings but it still gives you a start and makes you really aware of the closest landing sites. Both times new senders solved the problem.
I did finally relocate the sender unit to the firewall instead of the side of the engine oil pump where it's susceptible to vibrations and a quicker failure.

RandyL
03-11-2009, 08:01 AM
Dave's comments are good, I'd suspect the sender/wiring/gauge first. Seems like I've heard of lots of oil pressure systems giving erroneous readings and never heard of a 912 losing oil pressure (unless someone didn't tighten the oil tank lines properly.

In the Lycoming world you NEVER mount any transducer (sensor) directly to the engine becuase then it is subject to the relentless vibration of the engine. You therefore always run tubes of some sort to transducers mounted on the firewall or on an engine mount. Not there yet but this is what I plan to do with my Rotax transducers.

DesertFox4
03-11-2009, 03:17 PM
Relocation of the oil sender to the firewall is a very good idea. Not sure if many give it much thought but the stock 912 series comes with sender mounted out the right side of the oil pump. It is vulnerable to engine vibration failure in that location.
I changed my my model 3 back in 1999 and of course my 4 had the mod from day one. Murle Williams has a kit for this change with the proper fitting for the engine and stainless steel line to run back to the sender at the firewall. The bracket is easy to make. Murles' number is 602-978-0553.
John McBean at Kitfox Aircraft probably has a kit for this also but I haven't checked his parts catalog yet. He can be reached at 208.337.5111.

Peteohms
03-16-2009, 09:59 AM
I'm lazy, so my solution, which has worked so far, was to spray all the electrical connections with brake cleaner. Flew 10 hours with nary a glitch.