Failing CHT probe???

[Bluey]

Hi, during a flight this morning, I noticed that one of my CHT temperatures was lagging behind by about 10 to 20 degrees from the other one (912 UL). The one that was lagging was quite variable in that it was always behind the other and changing quite quickly by about +/- 5 degrees in a matter of seconds. At the same time the other CHT was very stable. This to me indicates a failing probe not a real problem (hopefully). I wouldn't expect the CHT to vary quickly at normal cruise RPM. Anyone had any similar experiences?

 

Bluey

 

 

[Mc Guyver]

Hi, during a flight this morning, I noticed that one of my CHT temperatures was lagging behind by about 10 to 20 degrees from the other one (912 UL). The one that was lagging was quite variable in that it was always behind the other and changing quite quickly by about +/- 5 degrees in a matter of seconds. At the same time the other CHT was very stable. This to me indicates a failing probe not a real problem (hopefully). I wouldn't expect the CHT to vary quickly at normal cruise RPM. Anyone had any similar experiences?Bluey

Swop your connections at the sender box and that will tell you if it is the thermocouple or the instruments

 

 

[Bluey]

Looks like the elecrical lead was a little loose. I jiggled it a little and now it is pretty much reading the same temps on both cylinders.

 

Bluey

 

 

[Guest davidh10]

Looks like the elecrical lead was a little loose. I jiggled it a little and now it is pretty much reading the same temps on both cylinders.Bluey

I had a similar issue, but it was intermittent open circuit. I cut a corroded, loose female spade off the end of the wire and replaced it. Fixed.

 

 

[Bluey]

Thanks David, that sort of thing will wreak havoc with these sorts of sensors every time.

 

Bluey

 

 

[cscotthendry]

Bluey:

 

Having just read your other post about the failing mag switches, combined with this problem, it suggests that you've got a grounding problem between the engine and the rest of the electrical system.

 

 

[Guest davidh10]

Bluey:Having just read your other post about the failing mag switches, combined with this problem, it suggests that you've got a grounding problem between the engine and the rest of the electrical system.

While a possibility, I would have expected that an intermittent earth would have affected all engine sensors, not just one CHT. Also the Mag Switch post indicated only one switch failed.

 

It is also not unusual for the two CHT readings to be different by a little. One is a front CHT, which gets cold air, while the other is a rear CHT, that gets pre-heated air off the leading cylinder. It is the jumping around that is abnormal.

 

 

[eastmeg2]

Corrosion in the contacts in the sender unit on top of the engine is a very real possibility. I experienced this on multiple engine parameters while flying up the west coast of the Yorke Peninsula in September and it was fixed by spraying some water dispersant (kindly provided by a local pilot at Kadina) into the contacts.

 

(I hope all you RAAus pilots enjoyed the "Kangaroo Island Trike Trip" article that Ian wrote).

 

Cheers,

 

Glen