Kill the weeds. Why are you thatching?

If you're overseeding soon, you're inside the window to "kill" the crabgrass. Any thing you put down to kill the crab grass will prevent new seed germination. However, you can put down a seed safe pre-emergent to keep any new weeds from sprouting up. I am going to use Tenacity during seeding. I just saw a starter fertilizer with pre-emergent by Scotts that can be used at seeding too.

Any thing you put down to kill the crab grass will prevent new seed germination.

Sorry, that's just not true. Pre-emergents combined with weed killers will prevent the new seedling from growing. Weed/grass killer will have no effects on the seeds. Just be mindful of what you are buying. Don't buy "name brands" buy based on what is on the product's label. For example, the Scotts' product just contain active ingredient in Tenacity. It's literally the same stuff in a set dosage plus filler.

Where do you live (city/state)? What type of grass do you have? Post pictures please so we can see what you see.

Hawthorne, NY I will post photos tomorrow morning when the sun is out. What should I look for to kill the crabgrass/weeds for my new overseeding? I am using Rebels seeds from Home Depot and lime and starter fertilizer I just need a weed/crab grass killer so I will be successful. The reason I plan on thatching before is to pull up the dead grass since I never bag my clippings and to scratch the ground to loosen the dirt for seeds.

You do not need to dethatch your lawn. Removing that material is a waste of good organic resources for your soil, which feeds your lawn. You may not need lime either. Do you have a lab test that says you do? Logan labs in Ohio is the go to lab we alll use. The $25 test is the one suggested and posting your results here will get you a customized plan.

Overseeding

This is the rye grass which looked nicer early summer.

The link you sent on overseeding states cut grass low to ground and thatch to remove dead grass for correct seed to soil. I just need to know how to eliminate the weeds during this time.

Spray Tenacity(mesotrione) at pre-emergent rate at seeding time. Or, apply the Scotts starter fertilizer with mesotrione.

j4c11 is the curator of the linked site. He has compiled the information so it is easier to help people. Sometimes there are changes in practice that are not reflected. He just didhis renovation using his removed material as ground cover.

Yes, you can remove all the dead material before you seed BUT you then want to put that material back on top of your seeds. That organic material feeds the soils and helps retain moisture.

I see bare dirt, but I don't see much thatch...

I will say this: the seed that was covered germinated significantly faster, at a higher rate and established better than seed that wasn't covered. The typical narrative is that the seed doesn't need to be covered, which is true, but it appears to me there are significant benefits to doing so.

In regards to dethatching: I'm a fan of great direct seed to soil contact, it has worked very well for me so far. I try to increase my rate of establishment any way I can, even if by just 5% (there's a reason that site is called Lawniac). It is also a lot of work, probably 90% of the prep work I do when seeding. If you have little thatch and the seed can make its way down to the soil, it's probably not necessary.

I was hoping the thatching machine would also help scour the dirt surface then I can add the seeds, fertilize and water.