catch can is filled up all the way to the top but "add coolent" light still comes on from time to time. i just change my water pump if it matters

 

The buzzer should sound with the 'add coolant' light.

Check the level at the rad cap, sometimes the system may not be able to draw from the overflow for various reasons.

If it is low then top up and get the system pressure tested to confirm no external leaks. If no leak is found do the dreaded o-ring test, detailed on RotaryResurection's website.


If the system was full when inspected then suspect the add coolant sensor at the centre top of the rad.

 

There is an air bubble trapped at the top of your radiator where the senser also resides. Look at the archives for a thread called "filling the radiator after rebuild" by Bob-the-normal

 

Agree, It sounds like an air pocket in the rad - the exact same thing happened to me and the procedure in the archives mentioned above solved it.