CHT erratic

[jnmeade]

912 ULS in FDCTSW @120 TT. Recently, R CHT has been showing readings 20-30 deg lower than normal, then it started showing very low readings, sometimes 0. Then the left CHT started doing it as well. EGT, oil temp and all other indications are it's not an engine problem but something in the display circuitry. I pinched the clip on the right lead and thought it helped, but no longer. It seems to start up about right and only start the erratic readings after 15-20 minutes.
Any suggestions on trouble shooting?

 

[Roger_Lee]

I would bet you are going to find a bad wire. If the connections on the ends on the spade are snug and that didn't help then cut them off and put new ones on. I have had 3 cases where the wire was broken under the plastic sleeve on the connector. Then trace the wires back and look for rubbed through wiring. A poor ground, but good connection usually makes them read high. A badly connected wire makes them go to zero. All the issue I have had with these has been at the spade connector. While your at it you may want to tighten the grounding block that is connected to your firewall behind the D120 in the CT. Tighten it from the inside of the engine compartment where the screw is located right next to the black protective tube for all the other wires and also inside the instrument panel.

 

[HeritageAviation]

I am also having this same issue in a FD CTLS with 1000hrs on it. After 20 mins or so I get an erratic high CHT reading on both CHT readings. I tried adding a jumper from the engine straight to the neg side of the battery, and it did not help. If I shut the dynon off and restart it, the erratic reading goes away.

 

[dynonsupport]

That's weird Heritage. How are you power cycling. Whole avionics stack? Or just the Dynon. Is the Dynon unit in question a FlightDEK-D180 or a and EMS-D120? If the former, does it have the internal battery fitted?

 

[HeritageAviation]

I have the EMS-120. I was cycling the master switch to turn off all power. I hunted the faulty ground some more, and don't seem to have any grounding issues. I removed the plug from the back of the unit blew it clean with some air and plugged it back in. I spoke with someone at Dynon support and he suggested using a 100ohm resistor from the prob connector straight to ground. He said I should read aprox. 150degrees. I wanted to attempt this while I was getting faulty readings. But I cannot seem to get it to do it again after cleaning the plug with air. Hopefully it is fixed but honestly my hopes are not that high.

 

[longhorn]

I have an RV-12 with a D-180 and Rotax 912ULS. The CHT's have started fluctuating from a low of 180 all the way to the alarm temp past 230 and back to +/- 180. I've checked the wire connections and ground, but the problem continues. It occurs after the engine has warmed and even occurred once when taxiing in with power at idle. What could be the problem?

 

[dynonsupport]

Is this only once they're up to temp? If so, you're not the first to report this behavior. Can you try swapping one of the CHT connections with oil temp at the sensor connection? They're the same sensor. This will cause the CHT to be oil temp and vice versa, so you may want to temporarily adjust or disable the alarming on them. But we're curious if the fluctuation follows the sensor or stays with the displayed element.

 

[dynonsupport]

On second look, actually, it's oil temp that other customers have seen issues with that we're trying to understand. CHT issues, not so much. This probably points towards a degraded component (wire, ground path) of some kind.

 

[Roger_Lee]

The Rotax CHT fluctuation most of the time comes from a loose connector on the CHT probe. If it is easy to turn crimp it down with some pliers until it is firm. It could also be a bad wire connection further down the line. CHT's are usually fairly solid and it's usually the oil temp that tends to fluctuate, but I have found you can minimize the oil temp bouncing with a really good ground wire. That said it still seems to fluctuate 3-5F.

 

[darrellpralle]

I also am having problems with cht on rotax. I am just in process of doing setup, have not started engine. Oil and egt temps read room temp but cht readings are not consistent with room temp. I have unhooked wires, no change. I have grounded wires, no change. I have checked wires for continuity, all ok.

 

[dynonsupport]

darrell - the problems that others have reported here are dynamic issues that only show up when the engine's running. If you're having problems at other times, there's something more fundamental at play. If you're using our D10/D100 series, not having the resistors intalled, or having the wrong values installed, can cause issues. What are you seeing, more specifically?

 

[darrellpralle]

I have skyview system with all the latest downloads, have rechecked that all is wired correctly, and just dont know what else to do. Also I cranked the engine today without starting, and got no oil pressure indication. If you want you call me at 580-747-4475. thanks

 

[darrellpralle]

did some more digging this morning. The cht readings are #1-106,2-4,3-39,4-61. Hooked cht wire to oil temp sensor-readings did not change. hooked oil temp wire to cht sensor & got oil temp reading. both cht sensor wires have .5 volt and checked all grounds, everything is grounded to a ground buss which is connected to batt ground which is connected to fuselage & engine block.

 

[dynonsupport]

Darrell - Unless you're using a Rotax 912, the CHTs and oil temp sensors are not interchangable. If you are using a 912, then you should only see 2 CHTs when things are configured correctly. Give our tech support staff a call at 425-402-0433 for some 1 one 1 help with your configuration.