This weekend the air cooling motor ran continuous on my Big Bear 400. Shortly afterwards the Oil Temp Light came on. Now when I start up the enginge the cooling motor kicks in immediately and the oil temperature light comes on within a couple of minutes. I changed the oil and filter and this is still happening. Does anyone have any suggestions or can you send me in the right direction to get some advice on this problem. Any help is greatly appreciated in advance.

 

Does the big bear have a external oil cooler? Maybe it is plugged or if you power wash to close they will fold over .Just a couple of ideas.

 

You say when you start the engine up that the fan comes on immediately? Is this after a ride or after a long cool down[overnight]? If so, you definetly have got a bad thermo unit [part# 4GB-83591-10-00]$54.22 or a faulty fan unit [part#5FU-e2405-00-00]$190.69 or it could even be both. is your machine still under warranty? Either way, you will want to take it to your dealer and have tehm test them to make sure you get the right part. Most dealers have a "no return" policy on electrical parts regardless of the reason, [unless they checked it for you and it didn't fix it]. This fact of no return will at least pay the labor [probally charge an hour minimum] to have the parts checked. Good Luck,KNOWSALOT.

 

bb400,
The oil temp sensor (Thermo-unit) completes the circuit to ground for the relay that supplys power to the cooling fan. On your quad this relay is under the seat or just under the rear plastic. During a test of the thermo unit you should hear this relay click (with the seat off)just a hair before the fan energizes or before your test light comes on if you have the fan unhooked. If it doesn't click the contacts may be welded closed.Also, if the wire from the thermo unit to the relay is grounded by accident such as pinched between the frame or motor during maintenance it will complete this circuit & energize the fan as soon as you turn on the key. Check your thermo unit by unhooking the wires and looking for continuity across the terminals of the unit. If you have a closed circuit while the unit is cold, it's bad. An open circuit means it's not the thermo-unit.To test for high temp continuity you must remove the unit and boil the sensor end in water to see if it closes at high temp.If your fan runs ands sounds okay and shuts off with the key then it is probably OK, you just have a circuit problem.I hope this helps you. The Yamaha manual is available for your bike and even tho it's pricey (tho less than a Thermo-unit)it is worth the bucks and can walk you thru checks like this one. Good Luck......