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Mystery Threaded Hole in Engine

JackinMichigan

JackinMichigan

Well Known Member
I hate asking dumb questions, but here I go again.

There is a threaded port in my IO-540. It is currently plugged with a red plastic screw in plug. It is pointed upward and sets just an inch or so forward of the oil filter. It is not the crankcase vent, or the oil cooler fittings since those are already install per the plans.

It appears to be a 3/8 pipe thread but I can only get a 3/8 pipe plug inserted by about one or even 1/2 of a thread. I am not going to put a wrench on it and force it into the hole. I have emailed Lycoming and they have not replied.

Can anybody tell me what that thread is for sure??
 
JackinMichigan said:
I hate asking dumb questions, but here I go again.

There is a threaded port in my IO-540. It is currently plugged with a red plastic screw in plug. It is pointed upward and sets just an inch or so forward of the oil filter. It is not the crankcase vent, or the oil cooler fittings since those are already install per the plans.

It appears to be a 3/8 pipe thread but I can only get a 3/8 pipe plug inserted by about one or even 1/2 of a thread. I am not going to put a wrench on it and force it into the hole. I have emailed Lycoming and they have not replied.

Can anybody tell me what that thread is for sure??
Click to expand...

Based upon your description it sounds like the port for the oil temp probe.
 
Last edited:
You Maybe Right

I am wrapping up my build. I don't remember installing a oil temp probe. (but I may have) Great reply, so now I start scrounging to see if I can find that temp probe..
 
Yeah, it's the oil temp probe location. Not sure what avionics you are going with. My G3X setup had the probe in the box with all the other sensors (CHT,egt, etc.). It uses straight threads with a crush washer.
 
Not the Temp Sensor

I checked, and my temp sensor is installed about 3" forward of this mystery hole. I don't know why I put my probe in the front hole instead of the rear, but my vague memory is that the probe did not fit into the rear hole.

I did find the plug, which is metal, from the hole that I am using for the temp probe. It appears to fit the thread in my mystery hole.

So, my new question is: Did I put the temp probe in the wrong hole?
 
JackinMichigan said:
I checked, and my temp sensor is installed about 3" forward of this mystery hole. I don't know why I put my probe in the front hole instead of the rear, but my vague memory is that the probe did not fit into the rear hole.

I did find the plug, which is metal, from the hole that I am using for the temp probe. It appears to fit the thread in my mystery hole.

So, my new question is: Did I put the temp probe in the wrong hole?
Click to expand...

Then you likely have your temp sensor in the wrong port.
The port in the top of the oil filter adapter, just fwd of the filter, is for the oil temp sensor.

It sounds like you have it in the port at the top left of the accessory housing, near the hole for the crank case breather. That port is not for oil temp.
 
This is kind of funny to me because I originally did the exact same thing.
I even had a temporary plug in the correct location (on the oil filter adapter) like you. I got tunnel vision and forgot the temp plug was there, a whole 3" away. The reason I stuck it in the "incorrect" location is because I was looking at the picture Garmin provides in their G3X install manual. They show it going in the forward location. When I talked to my mechanic, he talked me into moving it to the oil filter adapter location as that's where they usually are placed.
So, as far as it being incorrect, I'm not sure. Garmin apparently has theirs there.
After I ordered some new crush washers, it was a 15 minute job to get everything the way it should and safety wired.
 
I recommend you get an engine manual, with diagrams (worth a thousand words). Search the internet, download one for free.
 
clutch22 said:
This is kind of funny to me because I originally did the exact same thing.
I even had a temporary plug in the correct location (on the oil filter adapter) like you. I got tunnel vision and forgot the temp plug was there, a whole 3" away. The reason I stuck it in the "incorrect" location is because I was looking at the picture Garmin provides in their G3X install manual. They show it going in the forward location. When I talked to my mechanic, he talked me into moving it to the oil filter adapter location as that's where they usually are placed.
So, as far as it being incorrect, I'm not sure. Garmin apparently has theirs there.
After I ordered some new crush washers, it was a 15 minute job to get everything the way it should and safety wired.
Click to expand...

My guess is that's because the pics in the G3X install manual are of a 360 which might have a slightly different accessory and oil filter adapter config than a 540.
 
Auburntsts said:
My guess is that's because the pics in the G3X install manual are of a 360 which might have a slightly different accessory and oil filter adapter config than a 540.
Click to expand...

It is pretty much the same for all the 4 and 6 cyl Lycomings.

I think someone at Garmin just made a mistake.
 
Where do I get another crush washer?

Andrew, where do I get another crush washer?

I will get a engine manual on line...

Thanks guys...
 
Reviving old thread....

My engine came with an adapter inserted into the oil temp probe location. The adapter was safety wired and had a plug installed in it.

Question: Can I remove the adapter and just insert the probe into the hole (it fits and sees to have the right threads) or do i need to leave the adapter in place and thread the probe into the adapter (not sure if threads are same have not tried it).

This is a Garmin system.

Based on the Lycoming manual the adapter looks like part number 71600 "ADAPTER, Oil Cooler Extension"

Thanks
E
 
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