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  #1  
Old 08-16-2019, 08:35 PM
dabney dabney is offline
 
Join Date: Feb 2008
Location: valencia, ca
Posts: 216
Default RV12 Inaccurate oil temp sensor causing false high oil temps

I have a RV12 with the 912ULS ( non-builder) with 130 hours TTSN engine and airframe.

I have flown it for about the last 50 hours from January to now. The oil temps have always seemed to be a little high since I got it even flying in cool conditions with oil temps top of the green arc to the yellow arc-220-235. As the hot wx arrived in SOCal a couple months ago on a 90 degree OAT day I would have an oil temps 240-250 in the takeoff climb (5200 rpm, 75-80 kts) by the time I got to pattern altitude.

Based on advice I received here, I checked the oil cooler/cowl interface for leaks, cooling duct and seals around around radiator, oil lines for restriction, checked prop pitch, climbed shallower and faster. I found no deficiencies with these areas.

Finally, I decided to check the oil sensor (Rotax part no 965-531) for accuracy.

I calibrated two thermometers and a heat gun in boiling water. The thermometers were acccurate to within 2 degrees with each other and 212 F, as was the heat gun.

I immersed the sensor in water and took readings every ten degrees and compared it to the oil temp displayed on the D180. I repeated the test three times and obtained nearly identical temps each time.

The bottom line was that at an actual temp of 160 the Dynon indicated 175 and the spread increased gradually as the temp increased until at 230 actual (oil bath) the Dynon said 255.

Then just for fun, I removed the sensor from the cyl head port (same part number and interchangeable) and got just about the same results.

Next I bought a new Rotax oil temp sensor and repeated the sames tests and received the about same results with the Dynon reading from 15-25 degrees too hot.

So it seems to me unbelievable that three sensors could be reading that inaccurately. Is there something wrong with my test method?

If the test procedure was not flawed it explains my high oil temps. An indicated 255 oil temp which is getting close to the red line of 266 would be a more reasonable 230 +/- 2 degrees or so.

I talked to Dynon and confirmed with them that the D180 was setup correctly with the right sensor code which is 4. They offered no other explanation for the temp spread.

I am out of ideas about now. Tomorrow I plan to buy a non Rotax oil temp sensor which is 10mm x 1.5mm (same as Rotax part no. 965-531) and a stand alone oil temp gauge and see what I get.

I do not want to adjust the oil temp arcs on the Dynon to adjust for the errors, even if they could be changed.

Any other suggestions? Anyone else tested their oil sensor for accuracy?
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  #2  
Old 08-17-2019, 07:14 AM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 724
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Dabney-

Now that you have verified the sensors are not wonky, I would look into the wiring next.

Suggest you make a test wire with a fast on connector for the sensor end and crimp a new DB connector pin on the other.

Using the proper pin extractor (available from Steinair), temporarily remove the existing wire from pin 7 of the 37 pin connector that connects to the back of the D-180. Replace the wire you just removed with the test wire. What you are doing is connecting the oil temp sensor directly to the D-180 and bypassing the in-between connections made through the main board. If the readings are still off, you may want to also try running a wire from the ground on the battery directly to the engine (or better yet the body of the sensor) to insure you are getting a good ground for the sensor.

Have a look at the D-180 electrical drawing and you can see what the above accomplishes. If the above works, you have a wiring issue between the sensor and the D-180. If all the above does not work, the issue would appear to me to be inside the D-180.

Good luck,
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Last edited by John-G : 08-17-2019 at 01:41 PM. Reason: Clarification
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