Abnormal Engine Temp indications

[edneff]

I posted about this in August, but I have some further data points now.

I have been trouble shooting this for awhile and cannot seem to find the link between the electrical equipment and the engine indications.

Aircraft RV-7
Avionics: Garmin suite, G3X GDU 370 and GDU 375, GSU 73, GTN 650, GDL 39, GMC 305, PAR1000EX COM/NAV2 and audio panel, G3X displays powered from Backup Battery when Aircraft Master or Avionics Master is in the off position.

Symptom:
Temperature Engine indications of CHT and EGT will go down when certain electrical equipment is turned on.

Indications seem normal with Avionics Master on: (approximate) CHT 330, EGT 1000, turning the Avionics Master on or off has no effect on the engine readouts.

Turning Landing lights on, CHT drops by 110 degrees, EGTs by 300

With landing lights on, turning off Avionics master switch, CHT rises 50 degrees, EGT also rises.

Turning on Pitot Heat causes a similar drop in both CHT and EGT.

Turning on strobes alone causes some dancing up and down of the EGT's.
Strobes are Aero LED's Pulsars.

Suggestions welcome.

[rick9mjn]

Here are a couple of quick/cheep ideas.....check the ground/grounds, because both the landing light, and the Turning on Pitot Heat. Are higher current draw circuits,also the stobe. Look for a point all three connect. And with a little bit if luck and using sandpaper on the connectors could be the fix of your problem.
Good luck stay warm./rick
imho-imbw,,,,,,i my humble opinion,i may be wrong..
.
Standard excuses:
YMMV, Batteries Not Included, May Cause Erectile Dysfunction, talk to your family doctor, etc. ,
"Causes cancer in Kalifornia!"

[bret]

Is there a separate ground for the engine to firewall besides the battery to engine case or starter, and is a common ground used, like a forest O tabs ?

[edneff]

Thanks for the suggestions. There is a Plane Power 60 amp alternator in the aircraft.. The alternator is five years old. Could a alternator fault or an alternator that is not putting out 60 Amps cause this problem? And is there a way to test the output of the alternator while it is on the aircraft?

[Canadian_JOY]

Changes in engine readings are almost certainly as a result of poor grounding. Stop looking at the alternator entirely.

Make sure your engine crankcase (big hunk o' metal) is bonded with a honkin' big wire to the same place as all your electrical loads (landing lights etc). Maybe that's a bolt through the firewall or a brass feed-through for a forest-of-tabs on the cold side of the firewall. Your battery should be bonded either to this same location or directly to the engine block (two schools of thought, neither one is wrong).

The bottom line here is that your battery (-), the engine block, and the grounding point for your electrical loads all have to be tied together via very low resistance connections (big fat wires and very clean connections).

Changes in engine readings as a result of turning loads on and off are a clear indication you have grounding problems. If you're not comfortable troubleshooting this, find an experienced EAA'er to help. Look for the simple stuff like loose or dirty connections, bad crimps on those big fat wires, or your engine monitoring device not being properly grounded to the same location as the primary grounding point. Don't go looking for wild-*** possibilities like alternators. This is something truly very simple.

[bret]

I am only guessing but it sounds like the lights and pitot are grounded at the wing and not a return wire to a common ground, so in this case, find where they grounded the firewall to the battery and see if it moves, then remove it, clean and reattach. if there is not one, you can make one with...O.....say, 12 or 10 Ga. wire. And if you want to test before all this, take a DVOM and go to VDC one lead on the negative battery and one on the airframe, turn on the lights and pitot heat, should read < .02 VDC if more, add a ground wire.

[tim2542]

Originally Posted by bret

And if you want to test before all this, take a DVOM and go to VDC one lead on the negative battery and one on the airframe, turn on the lights and pitot heat, should read < .02 VDC if more, add a ground wire.

This is the same technique I was taught years ago by the Army, I?ve used it many many times over the years.
You are basically placing the volt meter in parallel with the circuit (or path in this case) you are testing. Use it for ground or power circuits same way.
Especially useful diagnosing starting problems but would be a good test for this problem also.
I also agree this is likely a poor ground problem.
Tim Andres

[edneff]

Thanks everyone. I am adding a ground wire tomorrow.