High CHT with Jabiru 3300A

[casimiroj]

Hi all,

We have recently mounted an EMS-D120 with a Jabiru 3300A. The problem is the following:

CHT readings at ambient temp are normal; also EGT; all of them matching aproximately the same.

Applying power, the CHT increases (wich is normal), but it goes to RED zone in 2 or three cylinders after just 1min climbing.

We have rebuilt many parts of the plane thinking in a ventilation power; we have specially rebuilt the air outlet. The problem keeps, but with an small improvement.

After a fly test, with most of the CHT at 120-130 degrees (EMS indication), we have compared with infrared thermal gun measures, and the difference is between 30ºC and 50ºC, depends of the Cylinder.

I am wondering if the real CHT is right, and the EMS is giving between 30 and 50ºC plus!

The installation has been done with Dynon package, using the brown extension cables, BUT, there is an aviation connector installed in the firewall and the brown CHT/EGT cables has been cuted and connected to this connector.

I mean, if you follow the brown cable towards the EMS, it ends at the firewall in the connector, and then starts again after the firewall inside the cabin. ¿could be the cause?

Regards!

 

[casimiroj]

And by the way, after 2-3min climbing almost ALL of the cylinders goes to RED zone, so the problem appears to be in all of them.

 

[dynonsupport]

There should be no junction at the firewall, since there will be a temperature change there. Here's the relavant excerpt from the manual:

-----
The thermocouple wires can be cut to a desired length if your application requires. If you need to extend the length of the thermocouple, you must use the correct type (J or K) thermocouple wire to accomplish this. It is acceptable to use non-thermocouple fasteners to join two pieces of thermocouple pair wire, provided the junction does not extend very far or have large temperature differences across it. Please contact Dynon Avionics to order extension wire.

----

If the junction used was for the right type of thermocouple (not likely used here), then the junction at the firewall would be OK.

We'd expect this to cause a lower than expected reading, not a higher one, so it doesn't quite explain it. But it's the first thing to start with.

 

[casimiroj]

The junction at the firewall is a 12 pin connector wich allows you to have an independent installation in both sides; it is not a thermocouple junction.

But, the reading looks to be higher.

Im going to test the reading removing one probe from the spark and introducing it into boiling water with known temperature.

 

[DBRV10]

Jabiru heads in some installations do get hot! What I would do is run a dedicated set of cables and see.

If you are using the under spark plug sensor they can be tricky to get a good seal too!

 

[casimiroj]

To use a dedicated set of cables is another possibility if the already installation matches wrong temperatures using a boiling water sample. Ill try first this, before purchasing another set.

I am using the plug sensor under the spark; what do you mean with "tricky to get a good seal"? Tight the plug as much as possible?

 

[dynonsupport]

Again - just to clarify: that 12 pin connector at your firewall will cause inaccurate temperature readings, even if they're not the cause of your current issues.

 

[casimiroj]

Update:

It is clear to me that the connector cause a mistake in the reading. We have recently tested the CHT probes (through the connector) with boiling water and comparing with an accurate thermometer. With readings from 30 to 120 degrees, the difference was not significant (usually 2-3 degrees difference over 100 degrees). In my opinion, i can live with that.

The important thing was that we found burned oil around the sparks JUST in those wich have the probes: EUREKA! it means, bad sealing, gases going out an high temp mis-reading. The thing was clear for us.

We tried to re-install the probes, but, the Jabiru 3300 space for that is extremely complicated. We almost broke some probes trying to fit it as much as we could. We also found that all the probes were incorrectly installed, placed after the washer, directly touching the Cylinder; as i understood, the order is (from inside to outside the cylinder): Washer touching the cylinder, probe and spark inside both, right?

We went flying after the modification, hoping that the problem was solved, but, almost nothing changed. RED CHT in 3 cylinders after just 500 feet climbing.

Any ideas? any trick to seal the spark and probe? we tied all of them strongly. In my opinion the space around the spark needs some manual modifications (cutting metal) in order to create space for the probe installation.

Regards!

 

[JR]

It is a common problem. Putting them with washer on first is not only difficult but doesnt stop the problem
I use some detergent mix squirted into recess then turn prop, if theres bubbles it needs repositioning. I also leave these plugs installed unless they really need removing for replacement
Depending on which heads you have, trimming a small section from fin above spark plug hole makes instal easier too.
Dont forget to install on front plugs one side, rear plugs the other so you are looking at same inlet or outlet valves
Some cut the ring off, insert end into small copper tube and adhere between fins next to head. Gets OK readings apparantly.

 

[casimiroj]

It is a common problem. Putting them with washer on first is not only difficult but doesnt stop the problem
I use some detergent mix squirted into recess then turn prop, if theres bubbles it needs repositioning. I also leave these plugs installed unless they really need removing for replacement
Depending on which heads you have, trimming a small section from fin above spark plug hole makes instal easier too.
Dont forget to install on front plugs one side, rear plugs the other so you are looking at same inlet or outlet valves
Some cut the ring off, insert end into small copper tube and adhere between fins next to head. Gets OK readings apparantly.

What do you mean with that? what plugs are you talking about? (sorry, my technical english is not very good).

And by the way, i also don't understand this sentence:

Dont forget to install on front plugs one side, rear plugs the other so you are looking at same inlet or outlet valves

The detergent trick is a good idea. Ill try it next time just to see.

Regards,

 

[DBRV10]

The important thing was that we found burned oil around the sparks JUST in those wich have the probes: EUREKA! it means, bad sealing, gases going out an high temp mis-reading. The thing was clear for us.


I am not sure what diameter hole you have in the CHT sensor ring, but from memory it is 14mm, and the spark plug is 12mm.

We found (when we had a jab a few years back) that you were better off carefully replacing the larger ring terminal with a 12mm one and carefully crimping the thermocouple into the new one.

I have also seen where the spark plug sealing washer is used, so what they do is unwind the sealing washer from the plug, insert the sensor ring and then refit the sealing washer (the right way around). This makes for a slightly lower reading, but its all about a sensible indication not an actual number. My guess is instead the official Jabiru numbers you may want to reduce them by 25degF.

All the best!

DB

 

[casimiroj]

We are using 12mm terminals.

The problem has been solved (we hope). We changed all the CHT probes to a bolt plug, instead of the spark (the bolt wich id over the exhhaust).

Now, the temps are extremely different.

We have contacted Jabiru just to know how accurate is the new place. We dont want to be misreading low temps. No response yet.

Thanks all for your help!

 

[DBRV10]

I doubt you will get a response from Jabiru.

Which bolt did you use?

Understand of course you could literally see variations of up to 50 degrees F and I would not be surprised.

What aircraft model is this engine in?

The best solution is always like the Lycoming sensor, and I am not sure if Jabiru are doing that now, however they should!

Remember you are not looking for all heads to be the same, nor a specific target number..........you are looking for indicative trends.

DB

 

[casimiroj]

I also doubt to get a response from jabiru; i already wrote in the past for another issue and nothing.

The bolt used is the one wich is directly over the exhaust valve, at left or right of the spark (is a little bit hidden inside the fins). I saw this recommendation here:

http://www.sonexaircraft.com/documents/instruction_sheets/CHT_Install_122007.pdf

The aircraft is a self made model that cames from an Spanish model called Moragon. The variatons around 50ºC !!! (not F)

Wich is the position of the probe in the Lyncoming?

Of course that i'm not looking for the same Temp in all Cylinders. I an checking the first things of all, green zone for all CHTs when climbing.

 

[DBRV10]

Well your next task is to improve the cooling flows into the engine area and out.

Remember that you need a positive pressure in the inlet and a negative at the bottom with no leaks to get proper airflow from one place to another.

Go seek the help of some other builders locally.

 

[casimiroj]

Hi all,

Finally, the problem was FOR SURE a bad CHT temp probe installation. Although the ring diameter is the correct one, there is no space to put it correctly, and there were gases coming out wich means bad temp reading. We installed the probe near the spark, in a bolt. The measure is not the best one, but at least the spark lies well turned with no gases coming out.

I founded also a company that sells smaller cht probes for jabiru 3300, just because of this problem: look for "AeroConversions CHT Probes" in google.

Best regards!!!!