I know there have been many threads on here but either I suck at using the forum search or the forum search feature just sucks. Anyway, my son’s 400 fan comes on when the engine warms up, then runs for about 2 or 3 minutes and shuts off. Then 30 seconds later it comes on again for a couple of minutes, then shuts off. Then comes on again 30 seconds later. It just keeps this cycle up. The rad is cleaned both front and back. What sensor turns the fan on? I know many have had fan issues with there 400 but this just started on his.