Oil Pressure Spikes

[Onex107]

This problem just popped up after 250 trouble free hours on my Onex. A few days ago I started the preheated engine and the oil pressure on the MGL Extreme spiked to 350 psi for a few minutes then back to 45 then back up to 350. After the oil warmed up it returned to normal and stayed that way for the flight.
I know there has been some VDO pressure sender problems. I'm now doing the Condition Inspection and when I did the warm up for oil drain and compression test I paid better attention to the pressure. I added a ground strap to the VDO with no change. Oil temp at start up was 60 degrees, air temp. Start and run at 1200 rpm, won't idle slower until cylinders warm up, the o.p. started at 45, then jumped to 350 and stayed there for a minute, then back to 45. It did that until the o.t. reached 80-85 then settled down and read normal for the rest of the warm up. I will look st the feed wire and RDAC connections also.
Today I pulled both pressure control valves. They were clean, fell out of the hole, no obvious dirt or scratches. I did smooth off the cut ends of the springs to avoid any friction there.
I don't want to add a mechanical gauge. What do you guys think? What do you recommend? Has anyone seen this before?

[MichaelFarley56]

Mine has done that several times; replace the VDO sensor as it’s gone bad. I’ve replaced mine on multiple occasions after it does the exact same thing. In fact I now keep a spare sensor in my travel tool kit for just that occasion.

[Sonex1462]

The VDO goes high if you have an open in the circuit and goes low if you have a short to ground. As things heat up and expand a bad connection can either get better or worse. Checking your wires and connections would be a good idea.

If you really had 350 psi oil pressure you should have oil coming out from some where.

On my very first flight I had intermittent high spikes in oil pressure after about 20 minutes of flying. It got much worse before I could land. I don’t remember the numbers but it would go from normal to extreme high and back to normal. It turned out to be a loose connection at the RDAC.


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[DCASonex]

Wearing out VDO oil pressure sensors is a chronic problem on Jabiru engines. If pressure pulsates, the wiper in the sensor wears through the wire winding and it creates an open circuit which is seen as maximum pressure.

David A.

[Onex107]

Thanks for responding guys. Your experience re-enforces my first thoughts. My friend, in the next hangar, blew his oil cooler one morning and I think he said the engine ran 13 minutes after leaving the oil on the ramp. Bottom cooler. Just long enough to reach a corn field. With the top cooler I would have a lot of smoke if that happened. Don't understand why these things cost so much and last such a short time. I think I'll take it apart to satisfy my curiosity.

[kmacht]

The stock VDO oil sensor isn't capable of measuring up to 350psi. The standard sensors are either 0 to 5 or 0 to 10 bar which translates to either a max of 80 or 150psi. The sensors are simple variable resistor that change as the pressure increases going from 10 to 184 ohms. Once it hits max pressure they don't go any higher than 184 ohms. The EFIS uses an internal voltage divider circuit to convert that resistance into a voltage it can read. The higher the resistance the lower the voltage measured. I agree with the above that you either have a bad sensor or there is a wire or connection causing a high resistance. If you don't want to pay shipping many marine and boat stores stock the VDO pressure sensors. I got mine at one for about $45 with tax.

Keith
#554

[WaiexN143NM]

Hi all,
instead of a vdo, look into the swift oil press senders acs sells.

WaiexN143NM
Michael

[WesRagle]

Hi Guys,

I'm working FWF right now. While staring at the firewall, wondering where everything should go, I thought of remote mounting the Oil Pressure sender.

Question: Are all of these sensor failures on sensors screwed directly into the engine? Do you guys think remote mounting the sensor on the firewall would reduce the failure rate?

Thanks,

Wes

[lgsievila]

Hi Wes,
My Dynon Installation Manual states, " First mount the oil pressure sensor to a fixed location using an Adel clamp or other secure method. The oil pressure sensor must NOT be installed directly to the engine due to potential vibration problems." I had my oil pressure sensor clamped to the engine mount when I was running the AeroVee and now have it attached the mount for the CAMit that I am running now. Still using the same sensor and no problems so far-over 200 hours. Of course I have an orifice in the oil line going to the sensor in case the line would break so I wouldn't lose all my oil at once.

By the way I have a brand new VDO 0-80 psi, 1/8 " NPT sensor for sale if anyone is interested-$35.00 plus actual cost of shipping anywhere in the US. Please see my post in classifieds for other parts that I have for sale.

[tx_swordguy]

I was having variable oil psi once the temp got above 170 F it was stable and good throughout rpm until it got above 170. It would then vary between 33-45 psi fairly rapidly. I pulled the pressure relief valve and cleaned and lapped it along with adding a washer and now at startup I get 60psi and at 180-190F oil psi is about 44-50 and stable. I did buy a vdo oil sending unit just incase and will keep it in the plane for a spare. It was rather expensive through avion aviaton at about 75$ with shipping. I only have 1 hr on it since doing that so we will see. I seriously doubt you actually got 350psi on that pump. you would have blown something I am sure. THis is on a jab 3300.