What is this in th IRS?

[Junbug]

So I was looking at the rear of my IRS and determining how to fill it. As i was doing this I saw this "feature", yellow arrow pointing at it. Its machined, polished and I can't really tell if it needs a plug, or if something I haven't gotten to yet, goes in there... I have a complete MkIV roadster, delivered 1/20/23, with 2018 3.55 Complete IRS Diff, delivered from FFR as part of my kit. Any help is appreciated...
https://thefactoryfiveforum.com/attachment.php?attachmentid=183842&d=1682908341

[Ford & Jeep Fan]

The fill plug is just under the other end of your arrow.

[Junbug]

So I was looking at the rear of my IRS and determining how to fill it. As i was doing this I saw this "feature", yellow arrow pointing at it. Its machined, polished and I can't really tell if it needs a plug, or if something I haven't gotten to yet, goes in there... I have a complete MkIV roadster, delivered 1/20/23, with 2018 3.55 Complete IRS Diff, delivered from FFR as part of my kit. Any help is appreciated...
https://thefactoryfiveforum.com/attachment.php?attachmentid=183842&d=1682908341

Thanks... I was tracking that... I'm just trying to figure out what the hole is at the pointy end of the arrow... before I fill it and end up with a mess!

[michael everson]

I think its a manufacturing boss. either that or holds something on the Mustang that we dont have. No need to plug it. Its a dead end hole.
Mike

[runamuk]

Mine came fully serviced, brand new in the box

[rich grsc]

You can stick a small screwdriver in it to see if it's 'blind' like Mike says, or open.

[Lidodrip]

It is used for some type of sensor, but not needed for our use. My differential came from a 2019 Mustang and had the sensor plug still in place (which I left).

https://thefactoryfiveforum.com/attachment.php?attachmentid=183847&d=1682945542

James

[Railroad]

Some models do come with factory coolers. I bet it is something related to mounting or feeding the cooler.

[q4stix]

It's a temperature sensor boss. Some models have it, some don't

[JohnK]

Mine also has it. I didn't do anything with it, and it didn't leak when I added fluids.

https://thefactoryfiveforum.com/attachment.php?attachmentid=106841&d=1557182268

[Junbug]

Great! As always the forum is well informed and helpful. Thanks folks!