Temp light comes on my 2005 500 atv after just 5min or so. Fan kicks on and off though. What could be my problem?

The fan is controlled by a thermo switch . It's located on the radiator and has power going to it always and when temp goes up it grounds circuit and fan come on.

Check oil level capacity, to ensure in specs. Check spark plugs, ensure its clean and correct plug for your quad.the only other could be is ign coil breaking down when warm. Check fire at plug when this happens. First ensure oil level is correct. Make sure your electric fan is on when bike is warmed up.

water pump, thermostat, air leaking into system, heat sensor malfunction.
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ATV Thermostat Replacement and Overheating Issues

theres two sensors one in the rad, and one in the left side of the jug

First check coolant level and correct if low. Sometimes this is all it is. If not, the cooling fan comes on due to a water temp sensor switch. Local auto parts place AutoZone, O'Reilly, Advance can help you find it. Probably bad. The other problem of dead battery is something staying on after car is shut off. Look for aftermarket electronics wired to a non-switched source.

Yuor fan brushes need to be removed cleaned and lightly oiled.

Most probably it's the fan relay.

General advice: Check that the thermostat is working and not stuck closed or open. Then make sure you have all the air out of the radiator. Also make sure the radiator fan is plugged in and working properly.

U should have two sensors for the cooling system one is nerr the thermostat housing for temp light / gauge ,one on the cooler at the bottem left side should have two wires on it need to pull them off connect the two togather. That should make the fan come on, if not, look for a popped fuse should invest in a handheld inferred thermometer ,there really cheap .get them on eBay for between 11 to 20 bucks brand new use it to test temp on coolant hoses to see temp on top and bottom .if fan does come replace cooling fan temp sensor.