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My Ground- Is it good or bad

Roger Lee

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Hi All,


Here is a little research I just finished and maybe it will help some.

The Rotax engine oil temp probe is extremely sensitive to resistance within a ground according to Dynon. Other probes and temps are sensitive also like the CHT's, oil pressure, EGT's, ect.. The FD grounds on the engine are on the water pump screw, then down to the frame then back up to the starter solenoid, then over the the reg/rec, then a ground wire runs up and into the instrument panel. If these are at all hand tight, but wrench loose you may have temps, pressures and headset noise. If you have any underlying corrosion it will also affect the ground. The owners in humid climates have had some issues with grounds and cleaning them up has helped.


I recently had an issue with oil temps bouncing 20F and a very slight headset noise. So to test the grounds I put a #4 wire from the battery negative to the drip tray screw up on top of cylinder #3. Then I ran another ground wire from the same point on top of the number #3 cyl. and ran it into the instrument panel along side all the other wires that run in the plastic sheath or fire sleeve which ever you have and attached it directly to the ground screw where all my other cockpit grounds are. I did not change or remove any FD grounds just added to them a more direct route with less chance for any resistance.


Time to fly and test. The oil temp went from a 20F swing to a 3F-5F swing and all other temps and pressures were rock solid. The very slight noise in the headset went away and the other aircraft I was flying with said it was more clear than ever.


If you are having headset noises, temp or pressure swings then you can try a test by hooking up a better more direct ground and see if your problems go away. You should use a #8 size wire to make a good solid ground. Usually just the one to the battery to the engine will work.

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I had a similar problem following an annual inspection. On my SW, there is a comb-shaped grounding bus that is linked to the battery with a firewall through-bolt. Roger has mentioned checking this before. I wiggled all the spade connectors and checked to make sure they were tight. My oil temperature and CHT swings went down to a minimum like Roger described. I had a noise in the headset and Lockwood ran another ground similar to Roger's description that cured my radio transmission carrier noise.

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