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Help FZR250 Temp gauge rises when lights are turned on?

Discussion in 'Yamaha 250cc In-Line 4's' started by Brandon Otte, Mar 12, 2020.

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  1. Brandon Otte

    Brandon Otte Well-Known Member

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    Good idea I'll wire one up this weekend.
     
    Brandon Otte, May 11, 2020
    #181
  2. Mike Green

    Mike Green Well-Known Member Premium Member

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    That voltage is high enough to cause serious problems. This could be due to an earth problem as well. Check the ground wire from the regulator and ensure it is actually at ground. If not, run a separate wire to a good ground. Kawasaki 1000Js had a problem like that.

    I've put a bike together from bins of bits and never had a bracket to the frame from the thermostat housing. I simply ran a wire from the thermostat housing to the frame. If you have any doubts about what is happening I suggest you do the same. Having an "extra" ground isn't going to hurt. The instrument wiring is pretty simple consisting of power, ground, and signal. It's very easy to trace. The gauge jumping up with the lights on does suggest a ground problem, possibly at the instrument cluster. Remember that there are light bulbs inside the cluster. If the earth return for them is not good is could cause the problem. I ran the earth from the instrument to the same earth point on my frame. All my earths go to the same 6mm bolt on the frame.
     
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    Mike Green, May 11, 2020
    #182
  3. Mike Green

    Mike Green Well-Known Member Premium Member

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    check the battery -ve to chassis with the engine running. Obviously it should be 0V. If not you have a ground problem. Running a wire from the battery -ve to ground should fix it
     
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    Mike Green, May 11, 2020
    #183
  4. Brandon Otte

    Brandon Otte Well-Known Member

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    Yeah that high voltage was caused by the reg/rec and is now sorted. Yup earth from reg is mint but will definitely run another earth from battery negative to the frame.
     
    Brandon Otte, May 14, 2020
    #184
  5. Brandon Otte

    Brandon Otte Well-Known Member

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    Sorry could you explain that again? What’s -ve? Is that earth?
     
    Brandon Otte, May 14, 2020
    #185
  6. Brandon Otte

    Brandon Otte Well-Known Member

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    Another question guys I’m hooking up my fan to the original switch on the thermostat housing. Does it matter which way round I connect the wires?
     
    Brandon Otte, May 14, 2020
    #186
  7. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    No it'll work either way around, neither terminal are earthed

    You could try it out before fitting it if you want, check the 2 terminal's for no continuity first, then test it out when it's sitting in the bottom of a cup with boiling water in it, should have continuity then
     
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    my67xr, May 14, 2020
    #187
  8. Brandon Otte

    Brandon Otte Well-Known Member

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    Cheers thank you, will try it shortly
     
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    Brandon Otte, May 14, 2020
    #188
  9. Brandon Otte

    Brandon Otte Well-Known Member

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    So I’ve plugged the fan wires back into the thermo switch and let it get to about 3/4 up the gauge without the fan switching on. I took it for a ride around the block to cool off - safe to say the thermo switch is no good without testing it for continuity.
    I connected the 2 fan wires together and the fan runs so I’ll try source a new switch locally.
    I have found them on eBay but I’d rather not wait a few weeks for it to arrive. Does anyone have experience sourcing them from super cheap or similar? And what temp should it switch?
     
    Brandon Otte, May 14, 2020
    #189
  10. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    The fan switch should turn the fan on at 95 degree's C
    They are the same switch for a few bike's,
    You should be able to get one from your local Yamaha dealer, ask for a fan switch for an FZX250 Zeal but it'll be expensive i'm guessing
    FZR250R FZR250 Genesis FZR400 FZR500 FZR600 FZR750 FZX250 FZX700 GTS1000 FZX750
     
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    my67xr, May 14, 2020
    #190
  11. Brandon Otte

    Brandon Otte Well-Known Member

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    Any idea where the gauge will read at 95?
     
    Brandon Otte, May 15, 2020
    #191
  12. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    My fan turn's on at about 3/4 temp
     
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    my67xr, May 15, 2020
    #192
  13. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    So it sound like the temperature gauge is behaving somewhat normally at least, given that you're having to let it sit and idle to get to the higher temperature range
     
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    ruckusman, May 16, 2020
    #193
  14. jmw76

    jmw76 Well-Known Member

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    You can test the thermo switch by placing it in boiling water and then checking for continuity with a meter. Just put the metal end in the water.
     
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    jmw76, May 16, 2020
    #194
  15. Brandon Otte

    Brandon Otte Well-Known Member

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    Yeah I've tried 6 different thermo switches, the one I bought the bike with, the one which came with the spare thermostat housing and another 4 from my parts guy and none of them have continuity. I tried boiling water from the jug and in a pot on the stove top at full steam with no luck. the best one of them got to was a resistance of 0.25ohms.
    So I've wired the switch back in until I can source a good one.
     
    Brandon Otte, May 16, 2020
    #195
  16. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    If it is 96 Celcius that the switch opens then you will find it hard to get that on a stove top with water... remember these switches are just on or off... so if the meter changed from 0 to 0.25 that should be enough to trigger the Fan relay and turn it on.
    I am assuming that the FZR250 has a fan relay...
    As long as the switch changes state at the high temp and then changes back as the temp drops... it is working if it is switching a relay.
    This gives you a better idea.
    upload_2020-5-16_16-46-13.png
     

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    Andych, May 16, 2020
    #196
  17. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    0.25 Ohms is effectively a short circuit, and may be the resistance measured on any corrosion or buildup in the surface of the brass so I'd say that one works

    You can measure the resistance in the leads themselves for example, very likely doesn't read zero, will likely read just above.

    I've got an older style analogue meter which has a dial to zero it to measure really low resistance as accurately as possible because the digital meter that I have doesn't have a button or function to zero the resistance measurement on the meter
     
    ruckusman, May 16, 2020
    #197
  18. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    I think you would need to be terribly unlucky to have 6 different Thermo switches and none of them work...
     
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    Andych, May 16, 2020
    #198
  19. Brandon Otte

    Brandon Otte Well-Known Member

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    Thanks @Andych
    So the ohm reading starts at around 1 ohm and drops as the temp rises but none of the switches every reach 0 ohms.
    I was under the impression that they need to achieve 0 ohms in order to allow current through.
     
    Brandon Otte, May 16, 2020
    #199
  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Current flow is a function of resistance - touch the positive and negative of a pair of jumper leads together - no effective resistance - sparks and microwelding

    From:
    V = I x R
    Voltage = Current X Resistance
    rewritten:
    Current = Voltage/resistance
    The charging system operates at 14 volts, so at 0.5 Ohms 28 amps could flow straight through a wire
    The fan is on a 5 amp fuse for comparison

    At 0.5 ohms when the system is hot enough that fan should be working, sounds like the system isn't getting hot enough.

    Remember that gauge was reading artificially high, BUT the fan wouldn't have been coming on near the red zone, (false reading) because it wasn't actually hot enough, which is why they wired in a bypass switch

    How cold is the air where you are now whilst testing?
     
    ruckusman, May 16, 2020
    #200
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