Just wondering who is using one and what temp the differential normally runs at.

Well, engine oil temp is supposed to be about 270 Farenheit I believe. I wouldn't think gear oil should get any hotter than that.

I would only think that this would be a problem in open road racing or high speed endurance racing. I know that the NASCAR guys actually run a pump and a cooler for the rearend.

I plan on running my car at open track road racing events when it's finally done.
I am just looking at things to add to the car while it's all apart.

Well in that case tap a hole in the bottom of the case so you can install a sender, and just get an oil temp gauge. You want the hole in the bottom, because the sender needs to be imerssed in oil to function accurately.

What rear are you running?

I am running a 99 LS1 rear end with Motive 4.10 gears.

Then you're good to drill and tap. If you had a 9" you'd need to weld in a bung.

If it is getting too hot I'm not sure what you can do about a cooler. All the ones I've seen are for 9" rears. They specially prepare the pinion with a cam section to drive a pump, or they run a yoke with a pulley on it. You may be able to do an electric pump, through a small oil cooler with a scavenge and a return port tapped into the case. Just some ideas...

Well, I am still building the car at the moment, but I want to do as much as I can while it's down.
I like the idea of the electric pump setup. I am going to look into that.