CHT and EGT readings on # 3.

[Stan]

I have a 1989 J model.  Since I have owned it I have continually gotten “lower” readings on both CHT and EGT on # 3.  I replaced the Insight G3 with an EI CGR-30P and “as expected,” as I did not change out the probes, the reading still remain the same.

 

The CHT reading show between a 21º to 32º difference between #3 and #4 (the hottest).

 

The EGT reading show between a 99º to 109º difference between #3 and #1 (the hottest).

 

Is this something to be concerned with or is it due to still having the factory probes still in place on #3?

[jaylw314]

The factory probe on most J's (I'm not sure it's true for all IO-360 powered Mooney's) is in cylinder #3.  Most 4 cylinder digital engine monitors have a probe that uses the same probe location on all the other cylinders, but they need a different solution for #3 since the factory probe has to stay for a non-primary monitor.  As such, many use a sensor that is a washer for the spark plug as an alternative, but that measured temp can be off by a lot.  It's usually hotter, but in my '86J it was always colder than the others by 40-50 degF.

Nowadays, instead of a spark plug gasket sensor, JPI uses a similar washer that goes under the factory probe, so it's much closer in temp.  Once I replaced it, it now is only about 10-15 degF cooler than the others.

Of course, you could always install a primary engine monitor like JPI's EDM-900, then you can replace the factory probe and have a consistent install for all four sensors.

EGT's on the other hand, can vary wildly between cylinders depending on how the probes are installed.  There is no standard factory hole for those, so they will not be consistent.  You care about when the EGT's peak and how they change with mixture.  You DON'T care what the actual temperature is. 

Short version is no, having CHT's for cylinder #3 that are way off the others is expected if it uses a spark plug gasket style sensor.  There's nothing in your description that sounds worrying.

[carusoam]

Stan,

Go immediately to the hangar...

Rip off the cowling... and take pics of the two CHT sensors, and EGT sensors on that cylinder...

You will probably notice all the other cylinders only got one set...

The ship’s gauges get first priority... so the extra JPI sensors got different locations...

The different locations cause the variation of temps, pretty significantly...

Don’t rush... you can take your time on this... 

But, post a pic when you can...

Download the data from the new engine monitor... send it to savvy... share, then post the link here....

If you have the TC that acts like a plug gasket, under a spark plug... swap it for what is called the piggyback sensor that mounts on the TC well very close to where the other TC is reading...

The piggyback is available from JPI...

PP thoughts only, not a mechanic...

Best regards,

-a-

[EDNR-Cruiser]

I have a weird reading for my cylinder #3 on my Lycoming IO-360 for a few flights now. All of a sudden the EGT of cylinder #3 rises approx. 100° above normal and at the same time the CHT goes down with the usual lag. I read quite a bit the past days but still can't get my head around it.
At first I thought it might be a partially clogged injector but that wouldn't explain the drop in CHT, instead the CHT should increase as I am still on the rich side of peak.
Same goes for a faulty spark plug... - the CHT should go up as well if a spark plug on this cylinder quits on the rich side of peak. The EGT sensor should also not be the culprit because of synchroneous decrease in CHT, same goes for a poor ground wire...

The file attached shows the readings of my JPI 900... - right from engine start the EGT of Cyl3 is higher than the others, coming down in sync after about 3 mins, passing the mags test and prop test as well as climb out, getting unstable between 13:30 and 13:35 and finally going way up 100° after 13:35 while the CHT comes down 30° with a little lag at the same time.  28 minutes later at about 14:03 the EGT comes down again and fluctuates up and down and the CHT goes up accordingly. At 14:22 the EGT goes up again and CHT drop accordingly for 3 minutes and remains unstable until landing.

Anyone ever experienced anything like this? Higher than normal EGTs and lower CHTs at the same time? Doesn't make sense to me, especially as I am running this JPI900 for years now and the values were always in sync and as expected. This anomaly showed up only a few days and flights ago.
Any help is much appreciated!

Edited November 8, 2020 by EDNR-Cruiser

[ArtVandelay]

Plug not firing. See page 16-17 of your JPI manual.

[EDNR-Cruiser]

6 minutes ago, ArtVandelay said:

Plug not firing. See page 16-17 of your JPI manual.

Hi ArtVandelay,
this would explain the rise in EGT but not the decrease in CHT!
A burned exhaust valve would explain this combination but I assume that this would result in constant readings of high EGTs and low CHT but not explain the dynamic fluctuations in the picture attached.

[ArtVandelay]

Hi ArtVandelay,
this would explain the rise in EGT but not the decrease in CHT!
A burned exhaust valve would explain this combination but I assume that this would result in constant readings of high EGTs and low CHT but not explain the dynamic fluctuations in the picture attached.

From Savvy website:
“Fouled or malfunctioning spark plug or ignition wire: Elevated EGT on affected cylinder only (usually by about 50°F or so). Slightly reduced CHT on affected cylinder.”

[EDNR-Cruiser]

Thanks a lot, Tom! That sounds more reasonable... - will check the plugs on cyl #3 in flight next time. For whatever reasons the usual mag check on pre-flight and after landing didn't show any misfunction on the #3 plugs.

[carusoam]

Bernd,

Can you post the data to Savvy, click share, then post the link here?

This allows us all to really look into the data as you probably have...

Unfortunately, the data only shows the one pic... so there is no file to search through the actual data...

Faulty spark plugs are often a challenge...

• champion have had varying and increasing resistance with hours...
• Tempest have had missing center electrodes fall out....

Which plugs do you have?

The tempest missing electrodes are interesting... some times the engine doesn’t notice it gone... other times under different conditions the plug skips...

PP thoughts only, not a mechanic...

Best regards,

-a-

[EDNR-Cruiser]

Thanks for all your advice, fellow Mooniacs. Luckily the problem disappeared after the previous flight. Last flight I had no more temperature issues at all with my cyl #3, all values stayed within their normal range. I checked magnetos in flight before but couldn't detect any anomalies so I assume that it was indeed a partially clogged injector causing the issue...

[Ragsf15e]

15 hours ago, EDNR-Cruiser said:

Thanks for all your advice, fellow Mooniacs. Luckily the problem disappeared after the previous flight. Last flight I had no more temperature issues at all with my cyl #3, all values stayed within their normal range. I checked magnetos in flight before but couldn't detect any anomalies so I assume that it was indeed a partially clogged injector causing the issue...

Just beware if it happens again... if it’s not the spark plug as suggested earlier, it can easily be early symptoms of a sticky valve.  Mine did exactly that.  As the valve rotates, sometimes it sticks, sometimes it doesn’t.  It’s erratic.  It would give warmer egt/cooler cht.  If it just stuck partially open and didn’t change, maybe it would be easier to diagnose, but that’s too easy...