Kavlico Oil Pressure Sensor

rv3flier · #1 04-23-2016, 06:56 PM

I had my Honeywell oil pressure sensor fail at 180 hrs TT and installed a Kavlico sensor instead. This required updating my Dynon D-180 to v. 5.5 to obtain the 5th sensor option for the Kavlico. My oil pressure normally would run near the top of the green upon start up about 70 psi. During my test run today, the oil pressure never registered more than 39 psi and, when warm, it varied between 15 - 20 psi depending upon throttle setting. According to Dynon's spec sheet the 0-150 psi sender will not register "0" when connected to the D-180, it will read 12 psi. They go on to say that "the sensor will display accurately at any pressure (in it's range) above this minimum measurable pressure. If that is so, then I presume that my oil pressure was dangerously low. Or, if the oil pressure scale is Red at zero psi and that is actually 12 psi then is it additive and the Lo pressure scale red/yellow is 12 psi --- then it's actually 24 psi?
Even then 39 psi + 12 psi = 51 psi is low for my engine on start up.

Now, if I got an air bubble in the line to the sensor (mounted with an adel clamp on the firewall) perhaps the air, which is compressible compared to oil, which is not, is interfering with the the reading?

Should I adjust the range scales for red - 0, red/yellow - 12, yellow/green - 29, green/yellow - 100 and red - 110

I think you can tell I'm a bit confused.

RFSchaller · #2 04-23-2016, 08:13 PM

The ranges have a lot of analysis behind them. I wouldn't change them. You may have a bad sensor out of the box. Sounds strange but it happened to me on an EGT sensor I replaced

Mich48041 · #3 04-23-2016, 09:29 PM

Air in the line will NOT affect pressure. The air and the oil have to be at the same pressure. If the oil pressure were greater than the air pressure, then the air would compress until it was equal to the oil pressure. The sensor does not care if the pressure against its diaphragm is from air or oil. It will still feel it.
If the oil pressure was constantly changing, then the air could expand and compress which could cause an erratic display. But I do not think that is a concern in this application. A small amount of air in the system will eventually be absorbed into the oil.

rv3flier · #4 04-24-2016, 08:05 AM

Interesting, I was thinking it would be the same as having air in a brake line and getting a "soft pedal" -- but I suppose after the air in the line compresses, like you said, it would reach a point where the pressure equalizes and the brakes are applied, just takes more pedal travel.

Well, now I either have a real oil pressure problem or a gauge/reading issue.

Sink · #5 04-24-2016, 09:08 AM

"Or, if the oil pressure scale is Red at zero psi and that is actually 12 psi then is it additive and the Lo pressure scale red/yellow is 12 psi --- then it's actually 24 psi?"

You do not need to add or subtract any psi from the reading. The reading is what the correct pressure really is from that sensor.
That said that does seem low and it is possible you have a bad sensor or a lot of air in the hose. These sensors are meant for fluids only and not a pneumatic pressure sensor.

Air in the oil pressure hose will cause fluctuating readings. Remember that a hose full of oil is not compressible and tends to give a solid reading. Even then our pressure can fluctuate some. Your real oil pressure in the engine can fluctuate in some applications approximately 5-8 psi (normal) depending on rpm and whether you have a good ground to the sender. Many people do get some air in their oil hose on installations, but depending on how your sensor is mounted (on the engine or remote mount, horizontal versus perpendicular) it should eventually vacate. Air at the tip of the sender can be different than a large air bubble in the middle of the hose. The amount of air will be a factor.

I would run the engine a time or two and see what happens with the pressure and not just at idle. We are more concerned with oil volume over just pressure by itself. The 912 rarely has a true oil pressure issue. It is usually auxiliary equipment or wiring.

rv3flier · #6 04-24-2016, 02:59 PM

Thanks for the feedback. I spun the motor with the starter, fuel off and mags off to get an oil pressure indication before I started the motor. During the run up I did I didn't notice any difference in the time it took the oil to reach 122*F and the oil level was at the top. No leaks anywhere and the oil and filter were changed 15 hours ago.

I'm going to try another run up or two to see if the pressure changes. If not, I'll try connecting a mechanical gauge to verify the readings.

BigJohn · #7 04-24-2016, 06:04 PM

Quote:

Originally Posted by Mich48041

Air in the line will NOT affect pressure. ............

Quote:

Originally Posted by Sink

"........Air in the oil pressure hose will cause fluctuating readings........

I love this forum! LOL!

Sink · #8 04-24-2016, 06:43 PM

Hi John,

Air in the line with fluctuating oil pressures on new installs are quite common. I get this question and see this quite often. It usually goes away after a flight. How fast it goes away depends on your oil sensor mount setup. It is far more common with a remote mount versus a direct to the engine mount.

rv3flier · #9 04-24-2016, 07:34 PM

Actually, the oil pressure wasn't fluctuating much. Started out at 39 psi and, as the oil temp came up the pressure gradually went down to 15 psi and then gradually back up to 20 psi at 4000 rpm during the mag check. It is a firewall mounted sender so the line is about 36" or more long and the line curves downward from over the top of the engine to the mounting point. When I installed the sender I used a squirt can to add oil to the line trying to keep it full, but I'm sure some air got in as the oil continued to drain back since I had to keep the line elevated to add the oil.

rv3flier · #10 04-29-2016, 04:08 PM

Ok, manual pressure gauge reads a normal 74 psi upon start up. However, with the Kavlico disconnected, the Dynon was still indicating pressure at 38 psi. From my notes and re-verifying the wiring connections, I have the Kavlico red to the Manifold Pressure sensor wire white/red, the green Kavlico wire to white/yellow and the Black Kavlico wire to black as shown on the July 2012 Dynon revision sheet. Dynon tells me that the RV-12 has different colored wires but couldn't tell me what they were. Can any of you tell me the correct wiring?

BTW, Joe Gores was correct, when I connected the manual gauge with 60" of empty line, it took a bit but the pressure came up to normal, so the air just compresses until it matches the oil pressure.