I've determined that I have some kind of restriction in my coolant passages. Most likely build up from hard water. Someone suggested using a little baking soda and water to flush it out.
Any other suggestions that DON'T include tearing apart the motor?
Any kind of water softeners that won't hurt any seals?

 

Any auto parts store will carry a rad flushing kit that comes with the appropriate chemicals. Water and vinegar works well too.

When you refill, just get distilled water from the local supermarket.