Erratic Low Oil Pressure

Catbird · #1 10-24-2012, 11:28 AM

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

Bastien · #2 10-24-2012, 11:55 AM

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.

JBPILOT · #3 10-24-2012, 12:53 PM

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

Catbird · #4 10-24-2012, 01:06 PM

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?

JBPILOT · #5 10-24-2012, 04:12 PM

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

You can read thru many posts on this subject.

John Bender

Kent Ashton · #6 10-24-2012, 05:38 PM

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.

Jetguy · #7 10-24-2012, 10:28 PM

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/communit...t=64145&page=9

rvbuilder2002 · #8 10-24-2012, 10:57 PM

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.

Dave12 · #9 10-25-2012, 05:32 AM

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.

JBPILOT · #10 10-25-2012, 06:22 AM

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.