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High CHT's on first flight with G3X touch: Data Log

cyrus

Well Known Member
Hi All,

Please have a look at my engine data from my test flight today and would appreciate thoughts on why the CHT's are high.

http://cirrusreports.com/flights/20MR/

I finally got into the air today doing a test flight with my Instructor after the new GDU460 install. I am not sure if this would have adjusted the timing of my pMag or LSE Plasma 3, but my CHT's are quite high across the board and one peaking extremely high. We did a few circuits to see if the temps would cool down with the mixture rich, throttle pulled back, and airspeed. They did a little but still too high.

I pulled the cowl afterward and did notice CHT probe for Cyl 1 wasn't installed as deep as the other probes. I fixed it but am unsure why that would result in a higher temp.

Baffles haven't changed and prior to this it was high 360-390 but rarely over 400 for more than a few seconds.

Previous to the install my oil temps did run high, my oil cooler is at the front and not what I'd consider being the ideal placement but my oil temps on today's flight didn't really alarm us.

I'm not sure if timing could do this (preignition?), or what else the culprit could be. Again, thoughts would be appreciated.

thanks!
 
Congrats on getting into the air! I thought I saw you taxiing out the other day. In my opinion your baffles/plenum look great. I would look into your timing and your fuel flow. My cozy with the o-320 burns about the same amount of fuel on take off and around the pattern at Hawthorne than you were burning. My Pitts with the souped up Io-360 burns nearly double what you were burning. Since your CHTs aren't above 500 I'd recommend you go to the practice area go to 7000 foot density altitude go full throttle and lean for around 10GPH and see what your CHTs end up at. You may have been climbing too slow after not flying the plane for a while. Also don't forget it's been pretty hot outside, especially at the altitudes you were at. Just a thought! See ya soon.
 
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Hi All,

Please have a look at my engine data from my test flight today and would appreciate thoughts on why the CHT's are high.

http://cirrusreports.com/flights/20MR/

I finally got into the air today doing a test flight with my Instructor after the new GDU460 install. I am not sure if this would have adjusted the timing of my pMag or LSE Plasma 3, but my CHT's are quite high across the board and one peaking extremely high. We did a few circuits to see if the temps would cool down with the mixture rich, throttle pulled back, and airspeed. They did a little but still too high.

I pulled the cowl afterward and did notice CHT probe for Cyl 1 wasn't installed as deep as the other probes. I fixed it but am unsure why that would result in a higher temp.

Baffles haven't changed and prior to this it was high 360-390 but rarely over 400 for more than a few seconds.

Previous to the install my oil temps did run high, my oil cooler is at the front and not what I'd consider being the ideal placement but my oil temps on today's flight didn't really alarm us.

I'm not sure if timing could do this (preignition?), or what else the culprit could be. Again, thoughts would be appreciated.

thanks!

I would look at your installation of the new CHT probes. Starting with the probes, make sure they are clean, no sealant of any kind either on the probes or in the wells. Probes fully seated but not over-torqued. Check to make sure your thermocouple wire is the proper one ( brown), and should run uninterrupted from your GEA 24 to the ends of the probe leads. Take care how you connect the wire to the probe leads, make sure you follow the instructions carefully and use the supplied hardware. I will say that on my RV-6 installation of the Garmin G3X sensors, my CHTs were running a little higher than they were before, maybe 20 degrees or so.
 
Just a thought, but are you absolutely sure you have the probes connected correctly to the wires for CHT? The way to test this is pull one out at a time and put a heat gun on it and see which number goes up. You first want to make sure you are reading them correctly.

How were you reading them before? Digital on all cylinders or ???
 
Same here

Hi All,

Please have a look at my engine data from my test flight today and would appreciate thoughts on why the CHT's are high.

http://cirrusreports.com/flights/20MR/

I finally got into the air today doing a test flight with my Instructor after the new GDU460 install. I am not sure if this would have adjusted the timing of my pMag or LSE Plasma 3, but my CHT's are quite high across the board and one peaking extremely high. We did a few circuits to see if the temps would cool down with the mixture rich, throttle pulled back, and airspeed. They did a little but still too high.

I pulled the cowl afterward and did notice CHT probe for Cyl 1 wasn't installed as deep as the other probes. I fixed it but am unsure why that would result in a higher temp.

Baffles haven't changed and prior to this it was high 360-390 but rarely over 400 for more than a few seconds.

Previous to the install my oil temps did run high, my oil cooler is at the front and not what I'd consider being the ideal placement but my oil temps on today's flight didn't really alarm us.

I'm not sure if timing could do this (preignition?), or what else the culprit could be. Again, thoughts would be appreciated.

thanks!

I installed the G3X in July, just before OSH, and have the same issue, CHT's running 25 higher than they used to. I did find issues with my Electroair ignition firing early and thought that was the cause. I have installed a new Electroair system but still have pre-ignition issues. The company asked me to send it back to be re-timed. I will do that today.

While flying this weekend, I by-passed the MAP so that the ignition would fire at 25 degrees. Engine ran great but I was still right at 400 CHT's in cruise. I am confused, is the current system wrong or was my old (VM-1000) system wrong? I am thinking more and more that it is the G3

Scott A Jordan
N733JJ
80331 1100 hours, now with glass.
 
I am with 6 Gun, I think you need a known temp (ideally close to the temp you are trying to check) and see what it tells you. An IR gun would be an easy non-contact way to get the head temp. You could take the temp right next to the probe.
 
Hi Guys, thanks so much for the replies. I was pretty freaked out seeing the numbers that high. Having calm responses helps.

Jesse, I used to have an EI UBG16 with digital readout. I felt it was pretty accurate, but had nothing to compare to.

Dave - yes that was me doing another run up to ensure all was in the green. Had some Com issues noise from LED's that I had to fix. My fuel flow was 14gph on take off and 10gph (full rich) in the pattern.

I did pull out Probe 1 and put a LED light I have that gets pretty hot on it, and it did go up in temp. So at least i know Cylinder 1 is actually CHT probe 1.

I look at the manual, and the install shows the CHT probes screwed in pretty far. Mine are a little less, so I'm hoping they're not over torqued but in far enough. And I did see brown wires running from the probes, will ensure they go right to the GEA24.

Next step is to heat up a probe and test it with the IR gun as suggested. Great idea.
 
Interesting...

Hmm, I've noticed the same thing after G3X Touch install last winter. Higher CHT's by maybe 20-30 degrees than what I've been reading for 16 years. So, as others have said, which one is correct, new or old? I will check vs my fluke the next time the cowl is off. I'll heat some oil up.

BTW, I'd recommend not using an IR thermometer, they are a bit limited. They are not just measuring the spot under their laser pointer, but a wider cone. The emissivity coefficient matters also.
 
Cyrus,

Just an observation that all of your EGT thermocouple probes were reading 70 degs F ambient before engine start and all of your CHT thermocouple probes were either reading the same or within 1 deg of that.

Your RTD oil temperature probe was reading 74 degs F before engine start, which is pretty close to the thermocouple readings.

Your OAT probe (another precision RTD) was reading 87 degs F before engine start, but the plane had probably been pushed outside and this probe might have been responding to elevated temperature from the pavement below it.

When I power up my avionics in the hangar with everything at ambient, I normally see all of these temperature sensors reading within a couple of degrees of each other.

Having all the EGT/CHT thermocouple probes on your plane reading within a few degrees of the oil temperature RTD is a pretty good indication that the thermocouple cold junction compensation circuitry within the GEA 24 is working as designed.

While this is no absolute guarantee that the thermocouple readings at high temperature are accurate, there is good evidence, using dissimilar temperature sensing technology, that they probably are working correctly.

A customer contacted us a couple of years back who was "very confident" that the CHT probes were reading high "and couldn't be right" when he was flying his new engine around with 500+ deg F cylinder temperatures (ouch). As expected, the readings were correct, and he had a serious timing problem.

Thanks,
Steve
 
Steve, right on. I think it's a good habit to get into before engine start to check all of your ambient temps. In my case, I check the 4 CHTs, 4 EGTs, oil temp, carb air temp and OAT. Usually all within a degree or two. When a probe starts to go bad, that's where you'll see it first.
 
Thanks Steve,

I was trying to think of a logical way to do a temp comparison and that makes complete sense. Will confirm the timing and was also thinking i can check temps on the ground with mag 1 running vs mag 2.

Cyrus,

Just an observation that all of your EGT thermocouple probes were reading 70 degs F ambient before engine start and all of your CHT thermocouple probes were either reading the same or within 1 deg of that.

Your RTD oil temperature probe was reading 74 degs F before engine start, which is pretty close to the thermocouple readings.

Your OAT probe (another precision RTD) was reading 87 degs F before engine start, but the plane had probably been pushed outside and this probe might have been responding to elevated temperature from the pavement below it.

When I power up my avionics in the hangar with everything at ambient, I normally see all of these temperature sensors reading within a couple of degrees of each other.

Having all the EGT/CHT thermocouple probes on your plane reading within a few degrees of the oil temperature RTD is a pretty good indication that the thermocouple cold junction compensation circuitry within the GEA 24 is working as designed.

While this is no absolute guarantee that the thermocouple readings at high temperature are accurate, there is good evidence, using dissimilar temperature sensing technology, that they probably are working correctly.

A customer contacted us a couple of years back who was "very confident" that the CHT probes were reading high "and couldn't be right" when he was flying his new engine around with 500+ deg F cylinder temperatures (ouch). As expected, the readings were correct, and he had a serious timing problem.

Thanks,
Steve
 
I hate shotgunning, but...

If someone else did the avionics installation, check to see if maybe they took out your P-mag jumper when they hooked up the tach.

There have been several reported cases of a failed Lightspeed MP sensor driving timing to max advance.
 
In addition to what Dan wrote above, the EGT values alarm me, they are very low. This along with the high CHT is likely to be from advanced timing.

Advanced timing beyond 25 degrees in a mag (about 23 at the plug) is not good at high power. A little bit (2-3) is helpful when at cruise power and LOP. Any more than this is not doing any good.

Remember depending on the system you have there will be no lag in the timing so at 25 you get a couple more degrees than the old magneto did...at the plug.

Get this sorted and if you can dial it back a bit all the better. The PMAG you can trick with setting TDC and then going past TDC a few degrees and setting it up there. Your LSE depends on which type. Get off the aggressive curves too.

A good indicator is EGT in the 1280-1320 range based on a lot of variables. ;)
 
All my temp sensors read within two degree of each other and the reported ambient temperature while sitting in the hangar.

A flight yesterday with the electronic ignition in MAP by-pass showed no difference in engine parameters in flight while running on each ignition system(one mag, one elec). Since several people have now reported similar issues, I have to believe there is something here.

Sent my ignition module out for a timing reset, will continue testing and report back in a couple weeks.

Scott A Jordan
 
My thoughts

Just a long shot, but did you connectorize the probe's wires? Are any of the probes tied to ground? Are the probe wires connected per manual? Is the setting for type of probe correct?
 
When I re-paneled a few years back I went from a Visions Micro 1000 monitor to the MGL iEFIS's. All my engine temps were different with the MGL than they were with the VM-1000. CHT's higher, OT higher and EGT's lower. They both would show the same ambient temps on all the probes while in the hangar. They both appeared to operate properly. I often wonder which one is right. It's not too easy to accurately heat a probe to 400 degrees or 1400 degrees. Finding a calibrated temp probe and attaching it to your sensing point and going up for a flight would be a good way to see what you've got. Otherwise you're just guessing.
 
Cyrus,


Not sure if you have checked this yet but TRIPPLE CHECK that you have the following;

1. The correct sensor setting in the G3X for K type for your EGT probes (assume they are) and J type for CHT probes.

2. Also just to be sure have you used the right wire. EGT wire is YELLOW and RED while the CHT is WHITE & RED.

I know of a similar result in NSW that was puzzling people far away (me) and it turned out the user had the wrong thermocouple type selected in the CHT probe menu.

Might be all it is......... ;)
 
Cyrus,


Not sure if you have checked this yet but TRIPPLE CHECK that you have the following;

1. The correct sensor setting in the G3X for K type for your EGT probes (assume they are) and J type for CHT probes.

2. Also just to be sure have you used the right wire. EGT wire is YELLOW and RED while the CHT is WHITE & RED.

I know of a similar result in NSW that was puzzling people far away (me) and it turned out the user had the wrong thermocouple type selected in the CHT probe menu.

Might be all it is......... ;)

Hi David, checked my settings on the G3X config this morning and then called Garmin. In my case, the G3X touch uses K type probes settings for both CHT and EGT. Both probes also have yellow and red wires.
 
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Cyrus, you ever figure this out and find a solution?
I am having similar high CHT issue with new install of G3X panel on a flying RV6A. CHTs are getting hotter faster and are 20-30F higher on average than they were with an older EI digital readout.
 
Cyrus, you ever figure this out and find a solution?
I am having similar high CHT issue with new install of G3X panel on a flying RV6A. CHTs are getting hotter faster and are 20-30F higher on average than they were with an older EI digital readout.

I've posted this before but it's pretty normal to see a 30d increase going from the older EI probe type CHT sensor to the newer style spring loaded sensor that most vendors currently use, including EI.
 
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