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Erratic Low Oil Pressure

Catbird

Well Known Member
Since first flight five months ago, I've managed to log 60 enjoyable hours in my new RV-12. 22 of these hours were spent flying from Washington to Alabama in early August with my dad; a wonderul trip.

Last Saturday on full power climbout, the Dynon Skyview oil pressure gauge began to fluctuate and dropped down into the mid-20's; the yellow zone. this had never happened before. I immediately pulled back on power and the oil pressure rose back into the mid-50's range. When I pushed the throttle in, the oil pressure dropped. Back off the power and the oil pressure rose. I landed as quickly as possible and assumed it was a malfunctioning sensor that was being adversely affected by vibration at full power setting.

Last night I plumbed up a mechanical gauge to the port adjacent to the oil pressure sensor on the crankcase. With the mechanical gauge lying in the passenger seat, I ran the engine with the wheels chocked to compare readings. Both the Dynon and mechanical gauge mirrored each other precisely throughout the rpm range, and I never could get the pressure to fluctuate and drop into the hellow zone. At one point, the pressure began to fluctuate a little and, most interestingly, both gauges flucutated together.

I'm coming to the conclusion this is not another failing oil pressure sensor.

Has anyone else out there experienced dropping oil pressure a full throttle? I really want to get to the bottom of this.

Thanks,
Jerry Gaulden
 
Hi Jerry,
I had the same erratic reading but on the oil temp sensor on my IO-375. I landed as soon as possible as you, checked on the Dynon forum and it is a "common" problem.
The reason is often a lose crimp or a grounding issue. On mine I spent 3 days flight testing (with ground check) to find that the lose crimp was the one on the sensor...
At first check, it looked good but once I did all the other checks I went back to this one and saw that when I try to pull (with a high load) the wire out of the crimp it moved approx 1/32 inch (this wire was the only one which was not soldered). I removed the crimp, put a new one, solder it and the problem was solved.

As you, my sensor reading did not fluctuate until I was airborne and especially full power or at high power setting. Pulling the throttle back solved the problem until power was added again.

In France, soldering wires on a plane is a never ending debate but I think it could avoid some issues and this one is a good example.

Hope this will help you.
 
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Hey Jerry - -

Do you have the latest pressure relief cone and spring and related things in the oil pump ? This has been discussed at length months ago. Yours might be new enough that you have the latest. Just asking.

John Bender
 
Jim,

I received my engine kit from Van's on May 13, 2011. I called Jim Scott in Arlington, WA this morning and he mentioned the spring in the pressure relief valve at the oil pump discharge. Next step will be to remove the spring/ball cartridge and see if I have the short one (older design) or the long one (newer design). Problem is, I won't know which one it is with nothing to compare it to.

As for loose crimp; this engine is running the Honeywell sensor with internal factory wire terminations. I'll check the terminations at the other end of the wires where they terminate in the instrument panel. Probably a good idea.

Thanks for the info. Can anyone lead me to the older thread on pressure relief valvesprings?
 
Jerry - -

put " honeywell oil pressure " in the search box above, and click on "posts".

You can read thru many posts on this subject.

John Bender
 
Be aware of ground loops, i.e., where the gauge and the sender are grounded in different places. It can cause a difference in potential at the grounds and screw up the readings. It can affect the readings intermittently. I had a fuel pressure gauge that bedeviled me for years, then oil pressure started screwing up. After I switched mine I have had no problems. Best to have all the engine gauges and senders grounded to the same spot on the engine block.
 
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Oil pressure problem!

Jerry there have been many problems with the Honeywell oil sender unit. At least 6 units that have failed on the RV12 have been reported on this form. It turns out that there is a fare amount of vibration up front where the sender unit is located and this is causing them to fail over a period of time. They cost upwards around $350.00 big ones. I recommend you order the relocation kit from Phil Lockwood in Florida and relocate yours to the firewall where there is a lot less vibration. See the link below to my long detailed thread on the problems
I had and how i fixed the problem.

http://www.vansairforce.com/community/showthread.php?t=64145&page=9
 
Relocating the oil pressure sensor...........
I admit I have no specific evidence to prove that it doesn't help, but there is also no specific evidence to prove that it does.

Builders that have relocated after a failure, and not had a recurrence, might have just received a defective sensor to start with and then relocated the replacement which might not have failed in the original location.

The value in making a change such as this has to of course be decided by each owner personally, but in my mind I tend to wonder is adding more weight, expense (cost of the kit plus shipping), and labor time, worth it without proof that it makes any difference?

Considering the number of instrument indication problems I am aware of that were caused by wiring connection issues, my bet would be that is very likely the cause of this issue also.
 
My sensor failed in 40 hours. The replacement has now worked for 110 hours and my readings are rock solid. Of course that was also after relocating it with the Lockwood kit. No question in my mind that it works.
 
Jerry - -

The remote oil pressure sender kit cures the display fluctuation issues also, which makes it a good benefit. It takes away vibration and heat issues. In general, I think it is a good mod for these reasons. I did mine a little different. I run the hose DOWN from the fitting at the pump, and run it back and zip-tied it to the rad hose. It also self-bleeds that way.

John Bender
465 hours.
 
Guys, Jerry says he put a MECHANICAL gage inline and it still did it. I'm thinking obstructed flow or something wrong in the oil tank. Jerry, is that correct that your mechanical gage also showed pressure drop?
 
Additional thought then - -

be sure suction hose is tight and not letting a little air in at the tank or pump. A better description of what fluctuations are being seen would help.

John Bender
 
Dave,

That's right. When running both gauges simultaneously, I noticed a short duration of erratic readings on both of the gauges at the same time. Problem is that the erratic readings were so short and slight that I wasn't 100% certain that it was real. This leads me to believe that the low oil pressure readings from last weekend were, in fact, real and not just erroneous reading due to sensor failure, bad grounding, or loose crimping.

That being said, I'll still go back this weekend and inspect/rework the wire crimp terminations behind the engine where the sensor wires connect to the panel wires. If I remember correctly, the sensor wires are solid conductor - not stranded. If so, then I can see how crimping could be problematic.

Of course, a close inspection of the oil hoses will also be performed to see if there is any possibility of air being pulled into the suction line. If this were the case, then it seems to me that the return line to the tank would returning an oil/air foam.

The pressure relief spring and related parts will also be inspected for premature wear.
 
Sensor Connectors

JFYI - Not sure if everyone knows, but Rotax offers a special spade connector for the three sensors on the engine. They look like the ones that Van supplied with the kits, but they are not, and they have a Rotax part number. You can really tell the difference when you make the connection. I bought 3 from Lockwood for about a buck. Lockwood discouraged soldering to the sensors. Too expensive of a part to destroy. Anyway, Rotax is well aware of the vibration that these connections are exposed to, and is comfortable with these connectors on their engine.


Tom
 
Tom,

I believe you are referring to crimp fittings or special spade connectors that connect directly to the sensors. In the case of my oil pressure sensor, the wires are factory terminated inside the sensor cover. The crimp connectors to which I am referring are located at the opposite ends of the wires where they connect to the instrument panel wiring behind the engine.

Jerry
 
Guys, Jerry says he put a MECHANICAL gage inline and it still did it. I'm thinking obstructed flow or something wrong in the oil tank. Jerry, is that correct that your mechanical gage also showed pressure drop?

Dave(the other dave), you need to humor us -12 guys a little. This oil pressure sender has been so bad, we will blame anything we possibly can on it!
 
Yeah, yeah, that's it. About a month ago I was having a little trouble dialing in the autopilot servos. Kept wanting to climb and bank to the left. I was convinced that the oil pressure sensor had something to do with that.
 
At work we were the UK dealer for Tecnams for two plus years. In that time, we changed many Honeywell oil pressure senders which had failed in various modes - full oil pressure, low oil pressure and no oil pressure.

The Tecnam singles behaved themselves but all 3 twins we sold/operated had them fail, hours between 50-400 - one had both engine sensors fail (at different times). Not so bad on a twin that shows no oil pressure but on a single, that is an attention getter.

As a result, on the 12, we have installed a (Tecnam) T-piece on the oil pressure port on the engine and have two sensors. The twin used the T-piece for the Honeywell sensor and a Hobbs switch for the Hobbs meter and door lock.

The Honeywell sender is still there on the 12 (until it fails...) driving the main SkyView oil pressure 'gauge'. We now also have a Kavlico sender on the T-piece displayed as a 'widget' next to the SV oil pressure gauge. If there is a discrepancy, I will believe the Kavlico sensor.

I kept telling the hierarchy at the Rotax and Tecnam factories that the Honeywell sender needed ditching - it is expensive and unreliable and gets both companies a bad name....
 
Jerry,

Everyone seems to be pointing to the sensor even though the mechanical gauge showed the same.

Suggest removing the oil pressure regulator components and examining. Simple to do.

Try posting your issue on CTFlyer, Engine/Rotax forum. Potential assistance there also.
 
All,

I'll be diving back into it this afternoon and tomorrow (Saturday), and will provide detailed information regarding the findings. Four areas will be inspected:

1. Electrical connectors behind the engine; specifically the crimp connectors on the solid conductor wires coming from the oil pressure sensor

2. Pressure regulator spring , cone, ball and other assiciated parts for premature wear and adherence most recent parts upgrade

3. Oil hose crimp connections and fittings from tank to heat exchanger to engine for possible air leakage of into pump suction

4. More detailed comparison of oil pressure readings between mechanical gauge and Dynon display

I think the most important thing here is to accurately diagnose the problem and then provide an effective solution. All of the discussion here has been helpful. Will advise.

Jerry
 
Jerry,

Everyone seems to be pointing to the sensor even though the mechanical gauge showed the same.

Suggest removing the oil pressure regulator components and examining. Simple to do.

Try posting your issue on CTFlyer, Engine/Rotax forum. Potential assistance there also.


It's ctflier. If you use ctflyer you get a defunct site if it comes up at all.
 
Well . . . I solved it.

Friday afternoon at the hangar I reached in behind the engine to jiggle the two spade connectors coming from the nefarious oil pressure sensor. Nothing violent or extreme; just a jiggle to show a friend which connectors were to be inspected. To my surprise, the red sensor wire immediately broke off at the entry to the crimped barrel of the connector. It must have been hanging on by a single strand. The wires coming from the sensor are multi-stranded 22 gauge, or possibly even smaller. I suppose vibration had taken its toll. Another contributing factor is that I was using a single crimper tool and not applying a second crimp at the end of the barrel to secure the wire insulation. Later in the project I had purchased a double crimping tool, but had not bothered to recrimp these connectors since they were 'hidden' down behind the engine. After reworking the wiring from the sensor to the D-sub connector behind the panel, my Dynon oil pressure reading is solid and relatively stable.

I apologize for the false alarm. Now if I can only find a way to blame my amateur crimp job on that Honeywell oil pressure sensor...
 
Hi Catbird, I had that happen while flying last winter. I was at 4500' and the pressure went to zero. Under normal circumstances I think most will agree that this situation is serious. I never gave it a third thought, I knew it was "that sensor" or it's associated wiring.
 
Considering the number of instrument indication problems I am aware of that were caused by wiring connection issues, my bet would be that is very likely the cause of this issue also.

Well . . . I solved it.

Friday afternoon at the hangar I reached in behind the engine to jiggle the two spade connectors coming from the nefarious oil pressure sensor. Nothing violent or extreme; just a jiggle to show a friend which connectors were to be inspected. To my surprise, the red sensor wire immediately broke off at the entry to the crimped barrel of the connector. It must have been hanging on by a single strand. The wires coming from the sensor are multi-stranded 22 gauge, or possibly even smaller. I suppose vibration had taken its toll. Another contributing factor is that I was using a single crimper tool and not applying a second crimp at the end of the barrel to secure the wire insulation. Later in the project I had purchased a double crimping tool, but had not bothered to recrimp these connectors since they were 'hidden' down behind the engine. After reworking the wiring from the sensor to the D-sub connector behind the panel, my Dynon oil pressure reading is solid and relatively stable.

I apologize for the false alarm. Now if I can only find a way to blame my amateur crimp job on that Honeywell oil pressure sensor...

Thanks for providing the follow up info to confirm what the actual cause was.
 
One more clarification:

The wires coming off the Honeywell oil pressure sensor are actually 24 gauge standed. These are probably the smallest or lightest wires on the entire plane, and by virtue of their smallness, pose a real challenge in attaining a durable and reliable crimp connection. I'm not saying that anything should be changed. I'm just saying that these crimp connections should be done very carefully and the wires AND spade connectors should be securely anchored to obviate the risk of breakage due to vibration or movement.
 
Another technique

Here is the way my friend Bill (A&P, IA) makes connections like this, and I have used the technique on a couple of especially sensitive areas. He uses an uninsulated spade (or whatever) terminal. Doubles over those really small wires and crimps, then solders. Then slides appropriate size of shrink wrap over the terminal and wire for an inch or so and shrinks to provide mechanical strength. Seems to work well. I'm interested in what you real experts think of this method.
 
Here is the way my friend Bill (A&P, IA) makes connections like this, and I have used the technique on a couple of especially sensitive areas. He uses an uninsulated spade (or whatever) terminal. Doubles over those really small wires and crimps, then solders. Then slides appropriate size of shrink wrap over the terminal and wire for an inch or so and shrinks to provide mechanical strength. Seems to work well. I'm interested in what you real experts think of this method.

Not saying that soldering is universally wrong, just that done improperly it can cause more problems than it solves.

The death to small wires is repeated bending concentrated at a small localized point. This doesn't have to be a lot of bend, just the small repeated movement induced by vibration.
The reason good quality connectors have two crimps, is the second crimp is a strain relief for the wire. It clamps on the insulation so that any bending /vibration is induced into the main body of the wire, not just the conductor strands.
The problem with soldering, is it is very easy for solder to wick under the insulation along the strands of the wire. This makes this wire very stiff. If this stiff area falls outside the strain relief crimp of a connector, you have a new bend concentration point where the conductor can now fracture beneath the insulation and be very hard to detect.
Covering with heat shrink helps, but it is still somewhat flexible so doesn't totally solve the problem.
I personally would never solder a connector on a wire that could be exposed to vibration (where on an airplane wouldn't they), unless the entire portion of the wire in the area of the connector can be solidly anchored so there is no possibility of movement (and if you do that, an unsoldered one will probably survive just as well).
 
I recently lost oil pressure indication in my 320 hr, 2009 D-180 RV-12. Two weeks ago on my way to the Amboy Fly-In from the SF bay area, just south of Bakersfield as I was climbing to cross the Tehachapis before a planned fuel stop at WJF I noticed the indicated oil pressure drop into the 20s before recovering to normal levels. This happened a couple times again in a rapid succession a few seconds apart, each time dropping further into the red. That certainly got my attention so I turned around toward Bakersfield Municipal where I landed without incident. By the time I got there I'd been flying with zero indicated oil pressure for maybe 5 minutes. There were no other symptoms. My friend (who was also going to the fly-in) was by coincidence nearby and picked me up in his Mooney and we continued the trip.

This weekend I returned to Bakersfield by car. I drained the oil, pulled the magnetic plug and found it clean. Replaced the Honeywell oil pressure sender with a VDO sender and purged the oil system. Probing the sender's resistance with a multimeter while turning over the prop by hand indicated I was getting oil pressure, so I rigged up a VDO gauge powered from the 12v plug in the cabin in order to completely isolate it from existing sensor wiring, EFIS, etc. That gauge indicated normal pressure. After an extended runup, a few high speed taxi tests and some laps in the pattern I flew home.

The sender had previously bounced around in flight when nothing else was changing, moving by 10-15psi or so in a few seconds but within the green arc. Knowing all the problems folks have had with the sender I already thought I should move it to the firewall at next annual. Now I certainly will.
 
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