First check sender, wiring, etc... all the easy and cheap stuff. If that doesn't fix it you probably need a new fan. We had to replace ours at 2,400 hours. If you run in dirty conditions they won't even make it that long. The book should tell you the specs that the fan needs to be at. Don't forget to clean centrifugal oil filter when in there. Supposed to be cleaned every 1,000 hours but I don't think many clean them that often.