Oil temperature sensor location

We did the engine preparation steps today and I am now confused about something. My Lycoming IO-390 came with a red plastic plug in the port on the top of the oil filter console, immediately forward of the oil filter itself. There was a metal plug in the upward-facing port on the accessory housing forward of the oil filter console.

On page 43-05, the oil temperature sensor is depicted in the port on the accessory housing, where my engine had a metal plug. The oil filter console is drawn depicting a flat surface where the red plastic plug is. This is where we installed the oil temperature sensor.

But if you look at page 51-06 figure 2, it looks like the oil temperature sensor is mounted on the oil filter console, where my red plug is.

Is the location where I mounted the sensor acceptable? Are there reasons for or against moving it to the other location?

Can I use the metal plug that was in my accessory housing to plug up the hole in the oil filter console?

For what it's worth, installation of the sensor would have been much easier in the oil filter console location, but what's done is done and I am not moving it unless there is a reason to do so.

Thanks for all hints!

Well, I don't officially know the answer, but I put it where the red plastic cap was--it does fit there. I guess I should have asked Lycoming, but the other port was painted and safety wired in place. you can see it on my RV-14 facebook page if you zoom in one a few of the pictures from when I hung the engine.

The one thing that I messed up was not safety wiring the oil temp sensor prior to mounting. Actually I safety wired it, but not correctly. Maybe you found the spot to wire it right away. I eventually found the hole to wire it to. It took me well over an hour and 10 or more attempts before I got the bloody wire in place to my satisfaction.

And yes it hurts like **** and bleeds like crazy when you poke yourself with the end of the safety wire.

unrelated but in the same section.

When you mount the mixture bracket and the adel clamps for the wires, you will need to purchase some new star lock washers (MS35333-39). Well maybe need is not correct, but I have heard that these washers shouldn't be used twice. Maybe I am wrong, but they did not look like they would work again-completely flattened out.

Your not going to want to hear this.

I installed mine in the same place too until I realized a oil cooler line went there.
It was a pain installing and safety wiring it there and another pain uninstalling it. I moved it to the other port in the back and then all the puzzle pieces fit nicely.

I have a picture of the back of the engine prior to working on it, which I just posted on FB (kens RV-14) The place where I put the oil temp sensor there was a red cap and there was a compression o-ring, which is the same as the one that comes with the oil temp sensor. SO I would agree with NYTOM that you probably put it in the wrong place.

Post a picture.

NYTOM said:

I installed mine in the same place too until I realized a oil cooler line went there.
It was a pain installing and safety wiring it there and another pain uninstalling it. I moved it to the other port in the back and then all the puzzle pieces fit nicely.

Click to expand...

I decided to just bite the bullet and put it in the right spot tonight. I don't think the place I put it actually does get anything. The oil cooler connection is to the left of this. But maybe you mean the line interferes with the temp sensor in the forward position. At any rate, I safety-wired the temp sensor to the plug after I put it back in, and it almost looks intentional.

Stockmanreef said:

And yes it hurts like **** and bleeds like crazy when you poke yourself with the end of the safety wire.
...
When you mount the mixture bracket and the adel clamps for the wires, you will need to purchase some new star lock washers (MS35333-39). Well maybe need is not correct, but I have heard that these washers shouldn't be used twice. Maybe I am wrong, but they did not look like they would work again-completely flattened out.

Click to expand...

I think they call it "lock wire" in Canada, and I was thinking about this earlier as I nursed yet another puncture wound and cursed that "safety wire" is one of the most dangerous things in the entire airplane.

Thanks for the tip about the MS35333-39's. I am ordering some stuff once I figure out what parts I need for the MAP line to the E-mag and I put a dozen of those little washers into my shopping cart.

iamtheari said:

I decided to just bite the bullet and put it in the right spot tonight. I don't think the place I put it actually does get anything. The oil cooler connection is to the left of this. But maybe you mean the line interferes with the temp sensor in the forward position. At any rate, I safety-wired the temp sensor to the plug after I put it back in, and it almost looks intentional.


I think they call it "lock wire" in Canada, and I was thinking about this earlier as I nursed yet another puncture wound and cursed that "safety wire" is one of the most dangerous things in the entire airplane.

Thanks for the tip about the MS35333-39's. I am ordering some stuff once I figure out what parts I need for the MAP line to the E-mag and I put a dozen of those little washers into my shopping cart.

Click to expand...

The port on the top of the accy case is fed directly from the oil pump and oil temp will be as it comes out of the sump. This port is usually used for either an oil cooler input feed or the ball/spring when no vernatherm is used. The port on the filter housing is the typical location and it's oil has come from the cooler, assuming the vernatherm is closed. It will read cooler than sump temps in these cases.

Larry