Erratic Oil Temp

[tjweathers]

I have a Dynon DEK-D180 and the oil temp is constantly erratic.  It gets worse and reads much higher when I turn on all the aircraft lights and systems (ie. the bus is loaded at 20 amps or more).

Normally, when I am running my aircraft during day vfr flight, I pull less than 15 amps.  The oil temp is rapidly changing in the range of 180-190.  When I fly at night and start turning on nav lights and landing lights or taxi lights, the oil temp jumps to 220-230 and is very erratic.  If for example I turn the landing light off, the oil temp will drop to 210-220 but is still erratic.  It seems, the more electrical load I am pulling, the higher the reading on the oil temp.

All other instruments in the D180 are reading normal and are steady.  Any suggestions?

 

[dynonsupport]

Oil temp is the sensor that is most sensitive to voltage changes. The 180-190 change you are seeing is only about 20mV of change. The jump to higher temps represents about 100mv.

The voltage change is coming from your ground between your engine and your battery/master bus. The alternator on the engine uses this ground path as part of the circuit, so all the current the aircraft is drawing goes across this connection. This connection must have a small amount of resistance, and the current going through it causes a small voltage drop. As the current changes, this voltage changes, and you see it on the oil temp sensor. The current in an airplane is changing all the time due to transponders, radios, autopilots, and all sorts of other things.

The solution to this is to get a bigger or better ground between the engine and your systems. First, check that the ground you have is free of paint, oil, powdercoat, corrosion, and any other insulators. We've seen painted engines, painted airframes, tiny wires, and all sorts of other stuff that causes this problem. If you're 100% sure that the ground between the engine and the aircraft is as solid as it can be and you're still seeing this, then you'll need to increase the size of this wire.

We've had a lot of people say they'll just run a ground wire from the oil temp sender to the EMS. Unfortunately this doesn't work, since this just becomes a very small increase in wire size versus the overall ground connection. You need to work on the main ground.

Good luck!

 

[randylsnarr]

I to have oil temps that rise with additional power draw. If I turn on landing Lights, , strobes and nav lights I get 12 degrees of increase in oil temp. I have 2 ground strap ribbons about 1" wide and 1/8 thick (automototive style) connected to the engine at 2 different places to the airplane firewall on a large brass stud. This same stud grounds the stainless firewall. Does this sound like I still need a larger gauge ground?

Randy
Lancair 235/320
N694RS