Hello everyone,
I need some help and will appreciate. I have a 2003 Grand Prix and a day ago I started seing coolant leak on one of the hoses coming from the water pump. I took a look inside the radiator and there was alot of gooey substance inside the radiator. The next day I added water and let it run for a while and I havent see any leaks "yet" with the exeption that one of the big hoses coming form the radiator seems to constrict or colapse as the engine got hotter. Does anyone have any idea if it is the water pump or just the thermostat?? Thanks for the help

I would run the car with the cap off for awhile, it sounds like u have an air pocket in ur system. Look around the intake for other signs of a leak, if ur coolant is gummy it is due to a intake gasket usally.
Check ur oil does it look milky?
As per the coolant leak at the pump, I would remove the hose clean the aluminum housing replace the spring clamp with a gear clamp and tighten good.

My recommendation would be to take the vehicle over to a GOOD shop (drive if temp is no issue; tow if overheating) to have them purge, inspect, and flush the system. Good luck on the fix.