I need a little advice......

[Hcsims]

I just got my airplane back after a complete panel upgrade. I added the Dynon engine monitoring suite to better integrate the system. I have a Grumman AA5B and noticed several items when 9i got it home. my main concern is my CHT's. The system indicates high 200's to very low 300's. Normal Grumman cylinder temps are in the upper 300's for the back cylinders. my question....shouldn't an avionics shop check that the data is correct? If I were to lean the engine using these CHT's and they are significantly wrong, I could quickly cause severe damage.

What is normal for a shop?

 

[Jesse Saint]

If a shop flies the plane they can check it, but that is not a common practice. I usually recommend that a customer comes and plans to spend the better part of a day flying locally, with me or one of my crew usually, to make sure everything is working correctly in flight. On the ground they can run the engine, but usually the CHT's don't get very high unless they do a long ground run. Next time you are at the plane, give me a call at 352-427-0285 and I'll help you check a few of the settings. Otherwise, you need to make sure the probes are wired correctly and installed correctly. If your cowl is open or off, I can help you check that as well. You may want to pull a probe out and put a heat gun on it and make sure the correct sensor is reading. I don't know what it would show, but if they hooked the EGT wires up to the CHT probes and vice versa, they could be erroneous readings, but I don't know if that would show the disparity you are seeing or not.

One easy thing to check is to see if they are reading ambient temperature correctly. If you go out to the plane on a 60-degree F day and they are reading 10F, then there is obviously a problem. You can also compare EGT and CHT temps compared to ambient. If they are both wrong, then it could be a wiring issue like I mentioned before. If the EGT's are correct and CHT's aren't, then it's something else probably. If they are all correct with the engine off, then the probes may not be seated correctly in the cylinders.

Again, give me a call, preferably with your cowl off, and I can help you run through a few diagnostics to see if they are installed, wired and configured correctly.

Full disclosure, I did not install this system for those who may wonder.

 

[Hcsims]

Thanks for the great info Jesse. The shop is going to get a few more days with it. There was some paint damage to my plane so they can take care of squawks. Afterwards, I’ll call if I have issues!

 

[unsafervguy]

jesse gave you some great advice. first thing to check is ambient temps with the engine cold. thermocouples are a know constant. they are a know mv/degree scale. if they are showing ambient then they should be correct across the range. you can also pull one and put it in boiling water and it should show close to 210 degrees. I would not suspect a crossed EGT/CHT connection, the difference in a J vs K type would throw the readings so far out of wack that it would be very obvious that something is very wrong.

 

[flyingcheesehead]

If I were to lean the engine using these CHT's and they are significantly wrong, I could quickly cause severe damage.

Leaning an engine using CHT? You're doing it wrong. EGT for leaning. CHT to verify that everything is working well and properly cooled. CHT lags too far behind mixture to make it a good way to lean.

 

[Hcsims]

The Dynon shop changed the thermocouples and now the temp readings are better.

 

[Jesse Saint]

Which ones did they use in the first place?

 

[Hcsims]

I do not know which one they used first. I have another question though. Is there a need to add a different squitter and add it to another location on the aircraft bottom?
I would have preferred using the old squitter location. Now I have another hole and two squitters.