Where to move OAT sensor to?

[AndreiC]

My OAT sensor was installed by a previous owner in the NACA air scoop on the pilot side. Unfortunately warm air from the engine appears to affect it — it usually shows about 10 dF warmer than it should, making it useless for knowing how close to icing I am.

I want to move it. I thought I’d move it to an inspection panel on the left wing, but it appears to be complicated to do this (for one, the wire provided by JPI is not long enough and I don’t want to go to the trouble of getting new wire, crimping new pins, etc.)

I’ve narrowed it down to two locations. One would be on top of the cabin, where ADF antenna was attached in the past, about 4” in front of the VHF antenna. The advantage of this would be that it is relatively easy to run the wire, and there is already a hole drilled from the ADF. A second option would be to put it either in front or after the battery inspection panel on the left side pf the fuselage. But this involves removing more of the interior to run the wire, and drilling a new hole.

Any opinions/suggestions? Thanks. 

[Ragsf15e]

30 minutes ago, AndreiC said:

My OAT sensor was installed by a previous owner in the NACA air scoop on the pilot side. Unfortunately warm air from the engine appears to affect it — it usually shows about 10 dF warmer than it should, making it useless for knowing how close to icing I am.

I want to move it. I thought I’d move it to an inspection panel on the left wing, but it appears to be complicated to do this (for one, the wire provided by JPI is not long enough and I don’t want to go to the trouble of getting new wire, crimping new pins, etc.)

I’ve narrowed it down to two locations. One would be on top of the cabin, where ADF antenna was attached in the past, about 4” in front of the VHF antenna. The advantage of this would be that it is relatively easy to run the wire, and there is already a hole drilled from the ADF. A second option would be to put it either in front or after the battery inspection panel on the left side pf the fuselage. But this involves removing more of the interior to run the wire, and drilling a new hole.

Any opinions/suggestions? Thanks. 

There’s an inspection panel on the front of the wing, just outboard of the wing root.  That’s no farther than the other options and it’s out of the sun.  I had the jpi one there on my F and it worked well.  Mine was on the pilots side which is away from the exhaust.  Right near the pitot drain.

[KSMooniac]

It's worth it to put it in an optimal location... several feet out from the fuselage under the wing.  Extending the wire harness is easy and not a good excuse to put it in a bad location IMO.  I expect your factory OAT gage is already out there, and if your JPI is a primary replacement you can replace the factory probe and potentially use it to pull the wires into the cabin if you're careful, and it's not secured in many places.  Otherwise, it is pretty straight forward to route wires through the front of the wing.  I've routed many wires and some tubes and it isn't awful.

Putting it on top of the fuselage is asking for direct sun impingement and perhaps still some radiated engine heat getting blown over it.  You correctly surmised that accuracy is vital, especially for your high-flying plane in an icy part of the country.  

[ArtVandelay]

You can adjust the OAT reading somewhat (I think +-6°) in the settings but if using for determining icing conditions I agree moving it would be better.

[ArtVandelay]

There’s an inspection panel on the front of the wing, just outboard of the wing root.  That’s no farther than the other options and it’s out of the sun.  I had the jpi one there on my F and it worked well.  Mine was on the pilots side which is away from the exhaust.  Right near the pitot drain.

Mine is on the pilot’s side vent where there’s no exhaust, it still reads high, I have another one on the lower wing I use if I want an accurate reading.

[BDPetersen]

I had probes in both the left and right side scoops, one for the JPI one for the G5. The readings were the same and not noticeably above ambient.

[N201MKTurbo]

Running the wire out to the wing is easy. Mine is a Davtron and I put the sensor in the same hole as the factory probe. It is in the first panel outside of the fuel tank.

[AndreiC]

44 minutes ago, N201MKTurbo said:

Running the wire out to the wing is easy. Mine is a Davtron and I put the sensor in the same hole as the factory probe. It is in the first panel outside of the fuel tank.

Can you guys please clarify where the factory probe on the J is? I don't think my E came with a factory OAT probe (or if it did it is long gone). A picture would sure help, but right now I was leaning towards the location @Ragsf15e suggested -- in a small panel on the wing, just outside the wing root.

[N201MKTurbo]

I wouldn’t put it in those panels. You have to remove them at annual to lube and inspect the aileron tube. They are kind of tricky to remove. If you put the probe on one of them it would make it harder to get them out.

The factory location is the first forward access panel to the left of the gas tank.

[Vance Harral]

Just get some type K thermocouple wire (https://www.aircraftspruce.com/catalog/inpages/jpiktypewire.php) and extend the wire as needed to locate the probe in the best location, which is under the wing (out of sunlight) and well outboard of the exhaust.

Sometimes people are reluctant to extend thermocouple wire because they've heard that doing so might be a problem.  There is a grain of truth to that, but only for very old gauges and/or extraordinarily long wires.  Modern temperature measuring instruments (even 1980s "modern") are designed to accommodate any reasonable length of thermocouple wire between the probe and the instrument.

Regarding the splices, thermocouple wire is difficult to solder, but you can use conventional barrel crimps or any other kind of mechanical connector.  I like these ones: https://www.aircraftspruce.com/catalog/inpages/eioverlapolc-1-10-05470.php.  They are an EI product, but they will work fine with your JPI system.

[AndreiC]

@N201MKTurbo I understand now what you mean. Can you please confirm though that if I were to run the wires through the front of the wing, the wire would go behind that inspection panel you were talking about (for the aileron tube)? If so, how do you keep the wire from getting tangled with the aileron tube?

[DCarlton]

I have three sources for OAT.  My EDM probe is also installed in the NACA duct and yes it reads about four degrees high.  More recently, when we installed my AV30, we installed the OAT probe in a forward inspection panel in the left wing (I believe it's just outboard of the landing gear; I don't have a pic).  This topic has been discussed before on MS if you can find it.  I believe the location we used is the same as the factory location (as mentioned above).  It's easy to run the wires; you may see grommets, wires, pitot tube etc in the same location if I remember correctly.  

[M20F]

I like keeping mine closer to the fuselage personally.  That extra ten degrees makes a lot of missions that would otherwise be scrubbed due to ice a reality.  Poor mans TKS but it works great. 

[N201MKTurbo]

1 hour ago, AndreiC said:

@N201MKTurbo I understand now what you mean. Can you please confirm though that if I were to run the wires through the front of the wing, the wire would go behind that inspection panel you were talking about (for the aileron tube)? If so, how do you keep the wire from getting tangled with the aileron tube?

There are already wires run through there, just tie the new wires to the existing bundle.

[AndreiC]

45 minutes ago, N201MKTurbo said:

There are already wires run through there, just tie the new wires to the existing bundle.

The reason I asked is that I *think* in my plane there aren't any wires running through there, or at least I did not see them when I opened that access panel. I'll check again this evening. (In fact I've always wondered where the pitot tube heating and the wingtip light wires are routed through...)

[N201MKTurbo]

In my plane, the autopilot and temp sensor wires go through there. I think the nav light and stall warning go through the wheel well and behind the gas tank. I believe there are holes in the ribs there that you can run the wires through to keep them away from the aileron tube. You could try to find the clips Mooney uses to clamp wires to the ribs.

[cliffy]

I moved mine to the outboard aft corner of the left wheel well

No panels to remove  or get inn the way of

[KSMooniac]

57 minutes ago, cliffy said:

I moved mine to the outboard aft corner of the left wheel well

No panels to remove  or get inn the way of

I wish I had thought of this!  Less drag.    

[flyboy0681]

On 4/24/2025 at 7:03 AM, BDPetersen said:

I had probes in both the left and right side scoops, one for the JPI one for the G5. The readings were the same and not noticeably above ambient.

Same here. Not noticeably different, and the wind speed and direction on my GI-275 almost always agrees with the tower when on final.

[AndreiC]

I ended up doing what was suggested and moved the sensor to the first forward outboard inspection panel past the wheel well. Running the wires through the front of the wing was more difficult, mainly because my forearm was too thick to fit through the inspection hole (to fish the wire out). Luckily my wife agreed to help. I have not test run the plane yet, but I suspect this is a good location for the sensor. (The JPI provided wire was just long enough for what I needed, in the end.)

[N201MKTurbo]

6 minutes ago, AndreiC said:

I ended up doing what was suggested and moved the sensor to the first forward outboard inspection panel past the wheel well. Running the wires through the front of the wing was more difficult, mainly because my forearm was too thick to fit through the inspection hole (to fish the wire out). Luckily my wife agreed to help. I have not test run the plane yet, but I suspect this is a good location for the sensor. (The JPI provided wire was just long enough for what I needed, in the end.)

This is what I use:

https://www.harborfreight.com/3-16-inch-x-33-ft-fiberglass-wire-running-kit-65326.html

[KSMooniac]

bent clothes hangErs can also be very handy if you tape the wire or a dummy wire/string to the end and fish through the spaces.  Then pull the dummy wire back through the route with the new wire.

[ttflyer]

On 4/24/2025 at 9:30 AM, AndreiC said:

Can you guys please clarify where the factory probe on the J is? I don't think my E came with a factory OAT probe (or if it did it is long gone). A picture would sure help, but right now I was leaning towards the location @Ragsf15e suggested -- in a small panel on the wing, just outside the wing root.

Our 1988 J had a factory OAT probe in a panel about half way out on the right wing. The panel was riveted in place, not an inspection panel.  We put our Garmin OAT probe next to the factory one in the same panel.  Not much work for people who work on airplanes... Don't have a picture handy but can get one next time at the airport.

[hypertech]

The installer for my JPI did that without talking to me and I was so pissed.  It looks terrible there and now I have a patch in the duct.  It belongs under the wing where the original one was.  It reads better and it looks better.  I got extension wires and had it moved - they didn't report any troubles doing that.  Afterwards I ended up with a second temp probe under the other wing for the G5.