2001 Pontiac Grand Prix indicates to add coolant?

Answer 1

Then add coolant? Being a GM vehicle, they specify Dex-Cool coolant... so, if that's what you're using, use that - don't mix different coolant types.

If you're frequently losing coolant, then you have a leak - pressurize the system... you can do this by running the engine until the thermostat opens up (to which end, you can simply inspect for your leak after a long drive), or you you can buy a coolant system pressure tester - they make both penumatic (air powered) and hand pump testers (the former is only good if you have an air compressor to use with it). The latter, you can buy at Harbor Freight for around $80, and it looks like it comes with the adapters you need for your system.. you can probably find similar (albeit more expensive) ones at places like NAPA, Auto Zone, et. al. Pressurize the system to the specified pressure rating of the cooling system, take a flashlight and inspect the cooling system for leaks (including the radiator, resrvoir, and all coolant lines), and also observe to see if the system holds pressure or not - it should).

From there, you find and identify your leak, drain your coolant, repair the leak, refill the cooling system, verify there are no more leaks in the cooling system, burp the cooling system, then top the cooling system off with coolant.

Hopefully I didn't make that sound too complicated - it's pretty simple stuff, really.