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Fan not working but works

Discussion in 'Technical and Troubleshooting Torque' started by VTRcamper, Apr 13, 2013.

  1. G'day guys I'm having an issue with my 2001 vtr 250, I recently started riding in to work and it takes about an hour to get there, during the back half I come across some heavy traffic and if I sit in it too long my bike overheats as the fan won't turn on. But when I get some air through the radiator it cools back down, so I'm assuming the rest of the system is ok.

    But here's the bit that has me scratching my head, when testing the fan switch and fan at home (with heat gun and temp sensor) the fan will work.

    If anyone has some ideas I'd really appreciate it.
  2. Does it properly overheat or does it just feel hot on your thighs?
    Is it possible that the temp for the thermo fan to work is just quite high? If so you can put a manual switch in for the fan.
  3. The switch could still be cactus and switching at too high a temperature, or there's a break in your wiring/bad connection somewhere, or else the fan motor is gone. Make sure the fan spins with your finger before you go any further. Try shorting the switch in place on the bike with a little piece of wire. If the fan runs then it's the switch being a pest, if not then you'll need to trace the wiring and find the problem.
    • Dumb Dumb x 1
  4. Sorry I forgot to say that I know it's over heating because yes I can feel it but mainly the temp light comes on.
    And as for the switch when we put the heat gun to it we also used a laser temp sensor and at the correct temperature it turned the fan on (so it does spin) but for some reason while im riding it the fan just won't come on.
  5. Ok, so just to be clear:
    Switch works at right temperature
    Fan runs when switch cuts in

    When you took the switch out coolant did come out of the hole, right?
    • Dumb Dumb x 1
  6. That suggests the switch works but isnt measuring water temp. Check the coolant level, to confirm the sensor is immersed in coolant. And check that the thermostat isnt stuck- a blocked thermostat restricts the flow of hot coolant to the radiator and cause a fan sensor on the radiator to read the incorrect temp.
  7. Correct but only during testing and not when I'm on the road.

    And I drained the coolant first but when I took it out I still had a touch come out yes.
    This is why I'm so confused...
  8. It's possible there's some blockage around where the switch mounts that's keeping a cooler pocket of coolant there. The thermostat could also be faulty as mentioned. I'd be inclined to test the switch with water rather than a hot air gun. Yeah it's slower bringing a saucepan of water up to temperature but something about using a hot air gun doesn't sit right with me.
    • Dumb Dumb x 1
  9. Just change the dam thing. That takes out one unknown in the equation. A switch shouldn't cost much but the cost of repairing a seized motor will.
  10. Suggests there is a blockage in the system.
  11. I have tested the switch with water as well and I have a spare switch due to another problem and the thermostat is fine as that was part of the old problem too.

    So if it is a blockage what would be the best way to flush it out?
  12. I'd disconnect the rad hoses use a garden hose, shoved (GENTLY! Just the tip) into the thermostat connection point to start. Move the hose around and run water through it from different direction to make sure it comes out of all the right places. Be careful not to damage any fins or the core.
    • Dumb Dumb x 1
  13. Do not pressurise your cooling system using garden hose pressure. It has way higher than cooling system pressures and you will find weaknesses in the bikes cooling system that will become leaks that you will have caused.
  14. Ok so I gave it a clean out, just draining the coolant, took out the fan switch and ran some water through it (not from a hose) and everything seemed ok. I then bleed the coolant and this morning on the way to work I had a gargling sound at low revs and when slowing and also the bike would backfire if i accelerated hard and let the revs drop quickly so now im confused at what has changed?
  15. How did you bleed the coolant? I'd be worried that the gargling was air in the system and if you run it like that for too long you could end up destroying the water pump and/or overheating again..
  16. Id be more worried about a crack in the head between the exhaust valve and water jacket or a piece of head gasket has blown out
  17. Start the bike with the radiator cap opened. And blip the throttle a couple of times, you'll see the coolant level goes down that should push all the air off the cooling system. Also check the ground wire on your fan. I had that problem when I disassembled the fan from radiator and didn't ground it back properly it was just not working when it should, but all the local component were good when tested.

    Also try to wire your fan off the thermo switch directly to the frame, if fan kicks in and your sensor is ok then it is a lost ground.
  18. Your garden hose is about 32PSI at most in a closed system. Your cooling system runs about 26PSI. That's not enough difference to rupture anything and you're flushing the system with it OPEN so you never get to closed system pressure. The pressure in the cooing system while open and being flushed never gets much above atmospheric. When flushing out with a garden hose you don't seal the system or even use full tap pressure, you just run a stream of water through it. You're not trying to blast anything out, just flush it.
    • Dumb Dumb x 1
  19. I bled the coolant by running it for a about 5-10 mins with the radiator cap off. I might pull it apart and try the whole process again but so far no overheating but it has been cold and I've had good traffic
  20. Make sure your fan kicks in otherwise you will bake your engine eventually.