how do i know if i need to replace my waterpump

Is your radiator fan working? Also if your AC works turn it on does the radiator fan come on with the AC?

Yes the fan is working and when I turn on the act it blows cold and the fan comes on

*a/c

How high is the gauge getting?Also ia the radiator fan on when the gauge is reading hot?

It stays a little over the half point and if I drive it long periods at a time it starts to hit the red when I'm stopped at lights. most of the time it will stay at half as long as the car is moving

If it will only overheat heat while idling then it sounds like the radiator fan is not working.So the radiator fan that is behind the radiator in the engine compartment turns on with the ac on and blows tons of air?

Whe the air is on the radiator fan does come on.

Then I would start by replacing the coolant temp sensor sounds like its not reading correctly and turning the fan on at the correct temo.Also inspect the inside of the connector to it if the terminals are blue or green instead of silver then you will need to replace the connector also.I have reolaced tons of them its a common failure.I have owned my 1999 saturn sl2 for 6 years and have replaced four of them so far.

Ok thanks

Keep me posted.