Some say cast impellers are the only way to go. That they do a much better job keeping the engine cool. I don't know if they are better or not. My car has a stamped steel impeller, and it doesn't get hot very often. Maybe a cast one would do better--I dont' know. If it was me, I would put in the new one. I would think it would less likely to fail before the old one. If it doesn't cut the mustard in keeping the car cool, put the old one back on. It seems like the divider plate adjustment, which has been much discussed, has as much to do with pump efficiency as anything.