bypass coolant hose

I have a 1990 2.2L 4cyl Cavalier Auto.

I have developed a leak at the bypass hose connection and was wondering if I have to drain the entire system to change this. Also if I don't have to drain the entire system, how much fluid am I looking at coming out while this is in progress.

You can change the hose without draining the system, and you will lose some fluid so catch it in a drain pan. I couldn't see you losing much more than a litre or so but its always better to be safe than sorry. Also when you remove this hose you run a high risk of airlocking your vehicles cooling system so make sure you are aware of proper procedures in removing airlocks. Can't say i didn't warn ya.