After installing dawnguard, my game will constantly freeze. Almost every four hours, the game will freeze. There is no specific quest or location in which it will always freeze. I turned off autosaves, and I tried to clean up some items I dropped. Nothing. Nothing but a patch can fix this, as far as I know. But if I need to do something that will fix it forever, please let me know.

American Dawnguard by the way.

Just throwing this out as an idea: Is your Xbox getting too hot?
4 hours play seems a little long and heat may have built up. The most I'll play in one sitting is 3hrs, with 2hrs being my normal session.

To be clear, I am in now way saying you don't have a problem. I get occasional freezes, sometimes after only 20min. There is no ryhme or reason to the pattern and it has, indeed, gotten a little worse with Dawnguard installed. All I'm suggesting is perhaps your situation is is being caused by excess heat.
Something to consider.

I remember making a thread like this. This happens to me as well I could play about 8 hours at a time before I had make my xbox take a rest (I know thats a long time). Now it's about same as you Frank about 4 hours at a time it crashes sometimes even shorter maybe 2 hours. Before I installed the game I got a freeze maybe once every 40 hours. After installing I got about 3 a day (this isn't counting that I don't even play as much as I used too). Well, anyways I quit playing until it's patched.

BTW my xbox would have turned itself off it it got too hot.

Do you have a slim version of the console or do you have an older version? That old XBOX 360s do not work properly with newer games.

slim