Engine Monitor - Odd Reading - Negative Temp

[Seth]

I had a trip a the beginning of April and during run up, my #1 cylinder showed negative temps.  This stumped me.  Everything seemed normal during the run up, but I also had cracked cylinders on this airplane before, so I finished the run up, sat there, ran it up again, everything seemed fine, except the negative temp on the#1 cylinder.

JPI EMD 830.  1983 Mooney M20J Missile 300.  No recent work, last oil change was two months prior.  I did not fly much in Feb or March, but did get just under 10 hours in during that period.

I stayed in the run up area, pulled out my phone, and looked up the issue online just to see if it was common.  Sure enough, negative temps normally means the probe is hooked up incorrectly OR is faulty/failing.  I chose to watch the engine monitor carefully on takeoff.  As I figured it was a probe that went bad.  

As it turns out, the correct engine temp readings came up with a little more heat.  The issue has not resurfaced since.  So it seems I may have a failing probe.

Anyone else have similar experience?  Once one goes, its it smart just to replace all of them?  I have six cylinders.  Or, just replace each probe one at a time as they fail?  I don't plan to replace it at this time, but I am watching.  Probes were installed in Sept/Oct 2011 at purchase/engine overhaul.

Thanks,

 

-Seth

[Marauder]

18 minutes ago, Seth said:

I had a trip a the beginning of April and during run up, my #1 cylinder showed negative temps.  This stumped me.  Everything seemed normal during the run up, but I also had cracked cylinders on this airplane before, so I finished the run up, sat there, ran it up again, everything seemed fine, except the negative temp on the#1 cylinder.

JPI EMD 830.  1983 Mooney M20J Missile 300.  No recent work, last oil change was two months prior.  I did not fly much in Feb or March, but did get just under 10 hours in during that period.

I stayed in the run up area, pulled out my phone, and looked up the issue online just to see if it was common.  Sure enough, negative temps normally means the probe is hooked up incorrectly OR is faulty/failing.  I chose to watch the engine monitor carefully on takeoff.  As I figured it was a probe that went bad.  

As it turns out, the correct engine temp readings came up with a little more heat.  The issue has not resurfaced since.  So it seems I may have a failing probe.

Anyone else have similar experience?  Once one goes, its it smart just to replace all of them?  I have six cylinders.  Or, just replace each probe one at a time as they fail?  I don't plan to replace it at this time, but I am watching.  Probes were installed in Sept/Oct 2011 at purchase/engine overhaul.

Thanks,

 

-Seth

Seth -- sounds like a probe going bad. I keep an extra one with me in case one fails but I wouldn't replace all of them (they are expensive). Before ordering one, I would just make sure there isn't a loose connection on the connector between the monitor and the probe. I had one loosen up. Also make sure the wiring isn't chaffing somewhere. I could see vibration causing a wire to move away from a ground.

What is strange is that you didn't mention any sort of error message on the JPI. Anytime I have seen a problem, the JPI displayed a bad probe error.

[ArtVandelay]

Try loosing and re-tighten the probes connections (they are ring connectors and a small nut&bolt), they can become loose or possibly a little dirty not giving a good connection). I thought I had a bad probe and turned out to be the connection.

[N201MKTurbo]

An open thermocouple will read the cold junction temperature. It will be the temperature of your instrument panel. To read an odd temperature it would have to be shorted to something.

[kortopates]

They all nailed it above, check for loose connection or chaffed harness. But since it came back to normal that is most likely pointing to chaffed connection that was grounding somewhere. So I'd follow the harness all the way back to the firewall and correct any chaffing as necessary.