Did you buy this Aveo new? What I'm really asking is do you know the history of it? The '04 was prone to early timing belt breaks. Another big problem is the POS plastic thermostat housing which has caused numerous overheats for Aveo owners. If you don't know the history of your Aveo (or had one of those 2 problems), you might consider a doing a compression or leak-down test (which hopefully will show nothing wrong).