Do tension pulley's go bad

Yes, a tensioner pulley can go bad -- it can lose tension, or the pulley bearing can wear. However, this may not be the cause of your overheating situation. Testing is required hands on.

If we had the engine size that would help .. IF it has the V/6 engine - many times the novice DIYer will mistakenly assume the 'water pump' is the belt tensioner due to it's physical size and location on the engine .. IF you're seeing antifreeze leaking in that vicinity, it will cause engine overheating.. In any event - qualified personnel at local auto repair facility will need to evaluate this for you.