I've had a tensioner go bad on my truck, so I've felt a weak one before, and this one still has some good life in it I think. Who knows though, I could be wrong. It's just like the water pump play, it is BARELY enough to even see, but you can feel it. I think I compare it to a new one at the parts store and go from there. I'd rather not drain the coolant AGAIN...since I just did it last week.