After filling with coolant, weeks later the resevior's empty and temp gauge runs hot.What caused this?
Leak somewhere. Try pressure testing system. Some auto parts stores will loan you the kit. This will allow you to inspect for leaks without engine being to hot to touch. A small inspection mirror will help you see in the tight areas. Look for signs of the coolant leak. When leak is found you will be able to figure out what action you need to take to repair it.
Like dandy stated, a leak somewhere, but as it is a 2002 I'm kinda leaning toward a blown headgasket or a cracked head.
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