High CHT indication on JPI 830

[Oscar Avalle]

Well here I am again with a question, that  hopefully somebody will be able to help me find an answer to.

I just updgraded from a JPI 700 to and JPI 830. I used the old EGT and CHT probes. 

Until I upgraded my CHT indications on the 700 were basically normal. Around 380 to 400 (I have a LASAR ignition system which raises CHT by 30 degrees).  After I upgraded, I started the engine and CHTs inmediatly went through the roof. On all 4 cylinders they reached 400 in less than 20 minutes and after take off they reached 500! Which of course made me land right away. But as I mentioned before...everything was normal until the upgrade...

Also, oil temp, oil pressure and EGT are in the green...I asked my mechanic to look into the baffling and the doghouse and he confirmed that everything looked OK. 

Unfortuntaley I was not able to check if the probes were working well...

So, I decided to call JPI and they told me that I may have some old GEM CHT probes with and a GEM harness which is not compatible with the 830...

My engine has only 17 hours since MOH...and I am flying out of a field with 5000 feet elevation...

Does it make sense what JPI is telling me or should I looked at something else...

[Taracka]

They should be able to tell you based on the edm700 serial number what probes you have.  I've heard of this problem occuring before so it's possible you have a probe incompatibility issue.  Do you have a factory cht gauge and if so what does that read?

[Oscar Avalle]

Unfortunately the factory cht isninop. But good to hear that somebody else heard about this

[Taracka]

You could pull a probe and check it in boiling water to see if it reads 212.  Also, think about if anything else has changed since the problem began that might be causing this.  For example detonation would cause a rapid rise in CHT and that could occur from things such as improper timing, bad or lower octane fuel, a baffling issue etc.  what model Mooney is this, what is your climb speed, and was the outside air temp unusually high?

[Oscar Avalle]

Dear taracka

Thanks for your comments. My mooney is a M20c. The engine a o360 a1d With a LASAR ignition. The engine has about 17 hours since major overhaul. Fuel is ok, timing was fine until until I flew her last time, the mechanic checked the baffling and it was fine too. Temperature was in the 80 and density altitude about 5000 feet.

The jpi was installed in 1990. Could it have been installed with gem probes? How can I find it out?

[M20Fan]

Your new device may be set for the wrong thermocouple type.  See pages 19 and 21 of the attached document.  Not sure this will help, but it may be worth a shot.

http://www.jpitech.com/manuals/01/INST-103%20RevE%205-17-09.pdf

 

[Cruiser]

some early JPI monitors were installed over older GEM engine monitors and worked with the old GEM probes. You could have an upgraded system. Check your logbook for evidence of an earlier GEM install before the JPI 700.

[Oscar Avalle]

Just to provide you with an update. I checked the probes and they are K type... So no problem there. I also checked the connections and I tested the one probe and everything is OK. Then I asked my AP to have a look again at the connections for the LASAR ignition. No problem there...

So I decided to start the engine and just see what was going on. I ran the engine for about 30 minutes on the ground (about 85 degrees and 5000 feet field elevation). One CHT (number 2) got up to 450... the rest behaved well around 390 to 423 (considering LASAR and temperature). Talking to some people on the field I was told that LASAR was a problem around here (high temps and thus high density altitude), because it raises the CHT... I was also told that several owners just went back to magnetos because of that...

So, thanks for all the inputs...

 

[Taracka]

The engine will not get adequate cooling being run on the ground for extended amounts of time,  if I'm stuck on the ground for a while and then take off my m20c temps can hit 430 to 450 if i'm not careful in keeping the climb speed 120 or more.  This seems to be the norm for this model and configuration ( i did lots of research).  With good speed management I'm able to keep temps below 400 usually but it's usually 70 f or less here in western wa.

[Taracka]

One more thing.  Make sure the JPI is grounded directly to the engine case per the installation instruction.  Grounding anywhere else can cause erroneous readings.

[Oscar Avalle]

Just to bring the story to a closure, JPI was not properly grounded. Now, the indications are normal, CHT 1, 2 and 4 in the lower 300 and 3 still hot, but not too hot.

[Johnnybgoode]

Just to bring the story to a closure, JPI was not properly grounded. Now, the indications are normal, CHT 1, 2 and 4 in the lower 300 and 3 still hot, but not too hot.

Fantastic to see a thread with resolution!

I am facing a similar situation and will pursue this solution.

Thank you!