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Low CHT in one Cylinder

macrafic

Well Known Member
The problem first surfaced when I noticed my CHT in cylinder number one would drop significantly when I pull back power. As soon as I advanced power, the CHT would go back up. I had reason to believe, based on input from several qualified experts, that I had a bad CHT sensor.

My A/P was hesitant to swap sensors with another cylinder to see if the problem would follow. Basically, I just wanted to confirm that it was a sensor issue. The reason he was hesitant was because he said the combination of stainless steel and aluminum often causes the threads to gall. He’s even seen the sensors break off in the cylinder as they are attempted to be removed.

Since then, the problem has worsened. In my last flight, CHT in cylinder number oneWas low all the time; anywhere from 100 to 150° cooler than the other cylinders.

I have an AeroSport IO-360 with steel cylinders, and the Garmin G3X CHT sensors. Has anybody had to swap out CHT sensors? Any issues? Has anybody heard of the type of problem that my A/P stated? He now has me hesitant to arrempt it on my own.
 
I have pulled probes with no issues, but they had only been installed for a year or two. I wouldn't be overly concerned, but would exercise caution if more than moderate force is required to get the cap turning.

That said, your symptoms don't sound like a bad probe/sensor. If the irregular cht change is always directly related to power changes and reads similar to others when cold and at full power, it is VERY unlikely to be a bad sensor. Possibly a wiring or connection issue, but far more likely to be an actual engine issue.

I would start by cleaning the #1 CHT connector at the probe, if it exists, and then inspect and clean the injector on #1. Most common cause of low CHTs is inadequate fuel supply (i.e. lean mixture).

Larry
 
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The CHT sensor itself fits into a bayonet adapter that screws into the cylinder - to swap only the sensor, you simply give it a slight push and a quarter turn - and it is out - no threads to gall. Swapping them is - to put it mildly - a piece of cake.

I think your A&P is not working with an open mind to actual current technology...

Paul
 
I can't recall ever having a problem removing a CHT probe or socket. It's always a good practice to use a little anti-seize when installing them, too.
 
If this is not a sensor issue, maybe that cylinder is speaking to you. Listen to it. Did the mechanic that you're working with tell you to just don't worry about it and fly on?
 
I should add, the engine purrs very nicely. Mag checks are just fine. I can run full Power, Rich Of peak, lean of peak, all configurations without an issue. Just did an oil change and nothing showed up in the filter. Oil samples being sent to Blackstone.

The reason that the sensor was suspected, is due to the fact that the A/P said
Cylinder temperatures do not drop Or rise that rapidly. When I pull or advance the power, the CHT follows suit in very quick fashion. The other cylinders, on the other hand, take much longer to respond to throttle movement.
 
Check you grounds between the engine and the battery. It sounds like you have grounding currents in the CHT lead....

I should add, the engine purrs very nicely. Mag checks are just fine. I can run full Power, Rich Of peak, lean of peak, all configurations without an issue. Just did an oil change and nothing showed up in the filter. Oil samples being sent to Blackstone.

The reason that the sensor was suspected, is due to the fact that the A/P said
Cylinder temperatures do not drop Or rise that rapidly. When I pull or advance the power, the CHT follows suit in very quick fashion. The other cylinders, on the other hand, take much longer to respond to throttle movement.
 
The CHT sensor itself fits into a bayonet adapter that screws into the cylinder - to swap only the sensor, you simply give it a slight push and a quarter turn - and it is out - no threads to gall. Swapping them is - to put it mildly - a piece of cake.

I think your A&P is not working with an open mind to actual current technology...

Paul

The Garmin is bayonet style probe (Alcor) which screws into the head.
 
The Garmin is bayonet style probe (Alcor) which screws into the head.

I just installed a Garmin probe today, and the adapter screws into the head, then the probe bayonets into the adapter - so you can swap probes without having to unscrew anything. Are we saying the same thing Walt, or did Garmin change their probes between shipments?
 
I just installed a Garmin probe today, and the adapter screws into the head, then the probe bayonets into the adapter - so you can swap probes without having to unscrew anything. Are we saying the same thing Walt, or did Garmin change their probes between shipments?

The last kit I ordered was a few months ago and it still had the direct screw into the head style threaded bayonet, sounds like they must have recently changed to the adapter style probe
 
The CHT sensor itself fits into a bayonet adapter that screws into the cylinder - to swap only the sensor, you simply give it a slight push and a quarter turn - and it is out - no threads to gall. Swapping them is - to put it mildly - a piece of cake.

I think your A&P is not working with an open mind to actual current technology...

Paul

Paul, you made me go back for some additional information. I was unaware that there are multiple types of CHT sensors (screw-in and bayonet). Unfortunately, mine is a screw-in and that is what Stein sells. I do not know about the compatibility between the two types, but I'm just going to keep them all the same. Thanks for the heads-up.
 
In case it helps anybody, the CHT probe on cyl # 1 WAS the problem. Replacement a non issue.
 
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