You've found a borer! However, it is a carpenterworm. 

Borers in oaks and other trees are usually a secondary issue. They take advantage of trees that are weakened from other causes (age, root rot, disease, lack of nutrients). 

Keep an eye on the tree this season for other evidence of damage. If the tree is losing leaves on its upper canopy, that would be a good indication that the borers and/or other factors have weakened the tree and that it will continue to decline.

The Red Oak is pretty healthy, however one of the limbs that was removed did have hollowing that looked like carpenter ants.  What can I do to kill these borers?  Can I use Permethrin (i have some) to treat the tree and surrounding area.  Anything else I can do to prevent the carpenter ants and this borer?  My neighbors have lots of dead wood on their property (over abundance) and I see a larger than normal population of carpenter ants.

Glenn Kowalske, P.E.

Here are a few more pics.  The site limited the size of my uploads.

Glenn Kowalske, P.E.

Here is some information I found on Carpenterworms.  Does the Michigan Extensiion have anything?

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1870&context=extension_curall

https://ipm.ucanr.edu/PMG/PESTNOTES/pn74105.html#:~:text=There%20are%20very%20few%20pesticides,when%20susceptible%20insects%20are%20present.

Glenn

Only a systemic insecticide applied into the soil at the base of the tree will have any effect on the borers. These are typically applied in Springtime and provide about a year of protection. They can be pricy, especially for a mature tree. 

The decay in the photos probably originated due to an issue or an injury that the tree experienced years ago. The carpenter ants are taking advantage of the weakened woods. Treating the ants with permethrin will kill them on contact but won't address tree health. If the tree branches hang over a home or structure, you may wish to consider having an arborist assess the tree's health to determine the risk of additional large limbs falling. treesaregood.org is a site to find certified arborists. In short, there isn't a "spray your way out of insect" solution in this case. While the systemic insecticide will address the borers, it won't fix the issue that has led to the internal decay.

Watering during drought and avoiding construction or other types of work near the roots will help keep this tree alive for many more years.  

Here is some information I found on Carpenterworms.  Does the Michigan Extensiion have anything?

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1870&context=extension_curall

https://ipm.ucanr.edu/PMG/PESTNOTES/pn74105.html#:~:text=There%20are%20very%20few%20pesticides,when%20susceptible%20insects%20are%20present.

Glenn

The tree is well over 200 years old (4 ft dia) and sits on top of a hill that was patially cut away a hundred years ago by a county road.  Beyond water, what can I provide to improve its health?

Glenn

Hi Glenn,
I've been following your conversation with David Lowenstein. 

Aside from watering in times of drought, there isn't much an oak will need to remain healthy over time. The tree has done well on the site for 200 years, so the site is providing everything the tree needs. Drought can be a major stressor for a mature tree, thus, the suggestion to keep it watered. 

Keep in mind that oak trees to have a projected lifespan, and with the decay it has experienced due to the carpenterworm, the structure of the tree is a bit compromised. The tree could live another 100 years with the damage! Or a weather/wind event could cause it to lose a branch tomorrow. We have no way to predict - especially without seeing the tree. 

The only way to have an idea of what might occur is to hire a certified arborist to come and look at the tree to assess it's structural integrity. Arborists do have technology that allows them to detect hollowed out trunks or branches (if they are within reach). Arborists are certified through the International Society of Arboriculture, or ISA. ISA maintains a website that makes it easy to find a professional. 
https://www.treesaregood.org/

I do hope this helps. Feel free to reach out if any questions arise. 

Thank you!
-Julie