Should i get my antifreeze flushed out and changed? Just tested with bulb tester and only 2 of 5 float?

Should i get my antifreeze flushed out and changed? Just tested with bulb tester and only 2 of 5 float - I'm in Phoenix AZ so not concerned about freezing, the boilover protection varies by only 10 degrees or so, is it worth it? Its an old car, color of anti freeze is fine - dont know when it was last changed. Thanks!