Erratic and high oil temp reading

[wbwillmott]

I just replaced the cowl and added a plenum but did not do any instrumentative work and now my oil temp has gone nuts.  I decided to replace the sensor because it always bounced around a few degrees.  Also, replaced the fuel pressure sensor because it's been bouning between normal and 99 and it is dead solid.  No work was done behind the panel.

First run did have the oil cooler on the firewall feed by a scat tube.  Fearful the temp was truly high, I moved the cooler back to the back baffle for plenty of air mass to pass through.

New oil sensor went up to 245 degrees and was bouncing around.  Put old sensor back in and got a bouncing 228 to 250 degrees.  Turn on landing lights and get 350 degrees which is the equivalent of a completed closed circuit.  Old sensor had 498 hours on it.

Checked with a volt ohm meter against the charts from Dynon. resistance shows a higher temp on both sensors now than the laser does anywhere on engine.  Unhooked the sensor wire and EMS shows 1 degree which indicates an open circuit.  Also, the temp the EMS displays agrees with the resistance shown on the sensor (obviously without the engine running).  Give impression that box is reading the resistance it's getting from the sensor.

Both sensors are bouncing around about 20 degrees.  Circuit load raises the temp by 90-100 degrees shown (landing lights, keying mike, strobes, etc..).  It didn't use to do this.

Put ground connection on the sensor with a #16 wire under a hose clamp and connected it directly to ground, no change.

Laser temp checked last 3 test flights and everything normal range.
3 minutes after landing, these are temps I got on the last flight - dipstick oil (185), oil filter (187 base and 155 top), engine case multple places (190-205), top of engine (201), oil cooler (154)....... EVERYTHING.   CHT's running in 350's.  Thank goodness because I'm not worried about the actual temp, just chasing down this goblin.

Turned off the engine and and the temp dropped and held steady at 207 after last flight even though I couldn't get a laser reading anywhere near that high anywhere on the engine, including the oil filter base and oil on dipstick.

When engine is running, only the oil temp fluctuates and drops after engine is turned off.

Engine is grounded (metal airplane) by #2 cable to bolt near battery and battery has a braided 6" ground strap.

Replaced sensor wire back to firewall and routed away from mags in case stray current getting in wire.  Mags were just overhauled.  Ring terminal solid. No change.

Can't find a nicked/frayed wire.

Made sure the nut/washer stack was clean and terminal couldn't connect to ground.

All other sensors on the engine that feed the EMS D10 are rock solid  (CHT's, EGT's) and don't vary when engine is running.

I've ordered another sensor (thsi time a GRT) just in case it may be a sensor.

One thing I haven't done is to pull the alternator connections and clean around them in case there is any oil or debris that allow some current cross over to the engine.

Another possibility is the D10 is sick and needs to be sent back but it seems to be reading the resistance and displaying properly the temp against what the Dynon chart values are.

Three flights and the rapidly fluctation display (only oil temp), excessive temp but does not agree with laser, 100 degree jump on load, is repeatable.

I'm looking for possible solutions or any other ideals.

Thanks in advance for any help.

 

[wbwillmott]

Based on tech support from Dynon in other posts, ground is the reason so I decided to tackle it from that aspect.

Pulled the ground from the engine to the airframe (connection is same post that the battery ground strap hooks to).  Cleaned both ends with 400 grit sandpaper and also cleaned the attachment areas.  Ground from engine to airframe is a #2 cable and is approximately 15" in length.

Tested it for 30 minutes in flight.  Everything look like it might be OK and after 10 minutes in flight, the temp rose and then the temp displayed was ranging from 217 to 219 changing every second or so and this was in level flight at 160 knots indicated.  The reported temp stayed constant ranging between 217 and 219 when it got to that point.  Upon decent, airspeed indicated was 185 knots and the temp stayed the same until I started to pull power and it dropped about 5 degrees.  Pulled up to hanger and after killing engine, it dropped another 12 degrees immediately to an even 200.  Also, in flight when I turned on the landing lights in flight, the temp went up 10 on the EMS.

Will say before I cleaned the ground connections, it was reading a fluctuating 228 to 245 degrees and any power drain such as landing lights, keying the mike would make it jump to 350 degrees.  Now it only fluctuates 2 degrees and jumps 10 degrees under load.

Got out and lasered temp checked the engine.  Bottom of oil filter was 185, oil on dipstick was 178, engine case ranged was similiar range and the hottest part of the engine case was 207, oil cooler was 154, NOTHING was out of range according to the laser.

All other instruments are dead solid.

New sensor coming from GRT just in case it is the sensor

OK Tech Support....any other suggestions on how to eliminate this goblin?

 

[jakej]

FWIW - did you check the Dynon to ground connections ?

What aircraft type ?

Is the panel made of Aluminium ?

Jake J

 

[wbwillmott]

FWIW - did you check the Dynon to ground connections ?

What aircraft type ?

Is the panel made of Aluminium ?

Jake J

It's an RV7 (metal airplane)
Panel is aluminum
Did not check the Dynon ground, however the unit is perceiving the circuit is less resistive by getting addtional voltages into the sensor. The ground the techs are talking about is the engine ground in which alternator voltages is getting into the sensor since the engine case ground is not as good as it should be. Also all other instruments are dead on and working perfectly. This is the ONLY instrument giving me fits.

Ground connection was cleaned and reinstalled and it is much better. However, it still fluctuates 2 degrees, and changes approximately 10 up on alternator load and down 10 after shutting down engine.

My gut is telling me several things:

1) Sensor is working but not reporting a good resistance number for the temperature since I can't get a laser reading anywhere close to the display temp.

2) Nature of the beast with this type of single wire sensor is going to be this way - reason for stating this is because it always fluctuated 2 degrees before but I never noticed a change with load since the temp was in the green and it may have been doing it and I never made a note of what the number was.

3) Ground is a #2 cable and is sufficient for a 60 amp alternator. Since only 20mv can make a sensor jump 10 degrees, it's also the nature of the beast with this design. I'm waiting on a GRT sensor with hopes that a new sensor will be a good report AND we take the engine case out of the electrical loop for oil temp monitoring.

 

[jakej]

200 knots

I have sent you a PM.

Jake J

 

[dynonsupport]

The fact that improving ground helped it, but that it's still reacting to current draw differences, points pretty clearly to a continued ground issue. The oil temp sensor is definitely the most sensitive, so that's why everything else, including CHTs and EGTs are OK. The alternate sensor might be worth a try, given how much effort you've already put into it.

 

[wbwillmott]

The fact that improving ground helped it, but that it's still reacting to current draw differences, points pretty clearly to a continued ground issue. The oil temp sensor is definitely the most sensitive, so that's why everything else, including CHTs and EGTs are OK. The alternate sensor might be worth a try, given how much effort you've already put into it.

I do think the alternate sensor will help since it doesn't use the engine case ground for the ground.

On the possibility the alternator is leaking voltage around the positive terminal, gonna clean it also.

Stranger things have happened!

 

[SammyQ2]

FYI - I had two GRT sensors go bad on me.  They started off working great, then each one failed when they hit around 205F.

I have called them, talked to the boss in person, and e-mailed, with no response from them, other than to offer to replace the sensor.

See my related post on the subject.

Sam