CHT’s and EGT’s skyrocketing randomly

[Pilot-To-Be]

I fly a Cherokee 180 and all was fine. We took it in for a routine oil change, spark plug cleaning and rotation. The mechanic replaced an EGT sensor on cyl #3 and two spark plugs.

I took it out for a test flight yesterday and now, the CHT’s are reading 400f-500f all of a sudden. I’m thinking it *has* to be false indications as nothing was done that would make the engine run so hot. I’m confused and stumped. I don’t know why it would indicate such hot temperatures all of a sudden.

 

[NoHeat]

Do you have engine-monitor data, in graphical form? If so, look at the CHT for rapid fluctuations, like 100 degrres in just a few seconds. Such a rapid change is physically impossible, for heating and cooling a metal cylinder, so that would indicate loose or dirty connectors, which is common.

 

[Pilot-To-Be]

Do you have engine-monitor data, in graphical form? If so, look at the CHT for rapid fluctuations, like 100 degrres in just a few seconds. Such a rapid change is physically impossible, for heating and cooling a metal cylinder, so that would indicate loose or dirty connectors, which is common.

I don’t, I’d have to watch the engine analyzer. My thing is, how could they have gotten dirty or how could anything have realistically changed with the work that was completed? It was perfectly fine when it went in.

 

[Dan Thomas]

Bad engine grounding between the crankcase and/or alternator case and firewall. Alternator output will find other paths to the airframe, and via temperature sensors is a common one. That little bit of extra current drives the indications higher.

 

[Pilot-To-Be]

Bad engine grounding between the crankcase and/or alternator case and firewall. Alternator output will find other paths to the airframe, and via temperature sensors is a common one. That little bit of extra current drives the indications higher.

Thank you, so in other words, it’s false indications? I was hoping to fly the airplane tomorrow but don’t want to burn up my engine. That said, again, I don’t see how the work performed would’ve affected engine temps, so my gut tells me it’s just bad readings from the probes.

 

[geezer]

"The mechanic replaced the EGT sensor on cylinder #3"

Most likely, he inadvertently caused a bad connection in the sensor system. Have him recheck EVERY wire he touched, or might have touched. I do not believe in coincidence in electrical problems just happening at a time when electrical work was performed.

Of course, do not hint that you think he was careless, he probably was not, the bad connection was near spontaneous failure, and he moved it.

 

[Domenick]

Dan Thomas and geezer are probably right, but was the replacement probe the same type, i.e., spark plug vs. bayonet?

 

[Dan Thomas]

"The mechanic replaced the EGT sensor on cylinder #3"

Most likely, he inadvertently caused a bad connection in the sensor system. Have him recheck EVERY wire he touched, or might have touched. I do not believe in coincidence in electrical problems just happening at a time when electrical work was performed.

Of course, do not hint that you think he was careless, he probably was not, the bad connection was near spontaneous failure, and he moved it.

He implies in his first post that all the CHTs were running high.

This thing needs addressing before further flight. Something like a slipped mixture control cable could lean the mix to the point the engine runs hot. I'd want to know that there is no reason for it to run so hot, then I'd be looking at the electrical connections, including grounding.

Electrical problems make up 90% of engine problems, from starting to generation to indication to spark. Yet the electrical system doesn't get inspected too well at all.

 

[FPK1]

I fly a Cherokee 180 and all was fine. We took it in for a routine oil change, spark plug cleaning and rotation. The mechanic replaced an EGT sensor on cyl #3 and two spark plugs.

I took it out for a test flight yesterday and now, the CHT’s are reading 400f-500f all of a sudden. I’m thinking it *has* to be false indications as nothing was done that would make the engine run so hot. I’m confused and stumped. I don’t know why it would indicate such hot temperatures all of a sudden.

Has this been fixed? What was the problem?