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Old July 4th, 2018, 03:12 PM   #1
DirtyMike
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Name: Kelly
Location: Boulder
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Motorcycle(s): 1987 Ninja 250

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[1987] Thermostat/Fan Diagnosis?

Hi,

I was looking online about how to diagnose the thermostat/fan/radiator pump and everyone says to first jump the two wires on the clutch side of the radiator to hot circuit the fan and see if it kicks on. The only trouble is I have no idea what two wires everyone seems to be referring too...XD

About the issue: When the key is turned the temperature needle moves ever so slightly, beyond that I have not seen the temperature rise after 5-10 minutes of idling at 3-4k rpm. I suspect something is up.

--Pictures here
https://imgur.com/a/wwq1lnM
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Old July 4th, 2018, 05:36 PM   #2
DannoXYZ
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MOTY - 2018, MOTM - Nov '17
Hi Kelly and welcome! You've been mis-informed. Here's what you want to do:


1. test thermostat - remove thermostat and place in pot of room-temp water with thermometer. Turn on heat (high) and note temperature where thermostat opens fully. Should be around ~150F.


2. test temp-gauge sensor (on thermostat housing, right side) - remove temp-gauge sensor and place in pot of room-temp water with thermometer. Turn on heat (high). Measure resistance (impedance) of sensor at various temps. At 175F = ~51 ohms, at 210-F = ~28 ohms. This is known as NTC sensor, negative temperature coefficient, sensor-resistance decreases as temperatures increase.

3. test temp-gauge sensor wiring and gauge itself (on thermostat housing, right side) - key ON, with disconnected sensor wire, gauge should read C. Connect sensor-wire to chassis-ground, gauge should read H.


4. test fan thermoswitch (left side of radiator, your picture above) - remove fan thermoswitch, place in pot of room-temperature water with thermostat, turn on heat (high) and measure continuity between centre terminal and metal case of sensor. Note temperature when switch closes/connects (ON, no resistance, full continuity) ~205F. Turn off heat and dump in some ice-cube to cool water. Note temperature when switch opens/disconnects (OFF, infinite resistance, no continuity) ~195F.

5. test fan thermoswitch wiring (left side radiator, your picture above) - connect disconnected thermoswitch wire to chassis-ground with short-jumper, fan should turn ON.


FAN NOT RUNNING WHEN THERMOSWITCH WIRE GROUNDED

6. test fan - disconnect wiring-connector at fan. Apply +12v to one terminal and other terminal ground to chassis. Fan should run!

7. test fan relay - trace fan-wring to fan-relay, back-probe connector leaving relay connected.
- measure voltage at white wire going into fan relay, should be +12v full battery voltage
- fan-thermoswitch wire grounded, measure resistance (impedance) on relay black/yellow yellow wire to chassis-ground. Should be zero-ohms, full-continuity.
- fan-thermoswitch wire grounded, key ON, measure voltage at relay blue wire, should be +12v full battery voltage

8. test fan wiring - leave fan-thermoswitch wire grounded
- measure resistance between black/yellow terminal of fan-wiring connector to chassis-ground. Should be zero-ohms, full continuity.
- key ON, measure voltage at blue terminal of fan-wiring connector. Should be +12v full battery voltage



Do in order, There are many difference independent components that work together in cooling system. These test uses boolean-logic and process-of-elimination to determine which part is bad. There may be more than one bad part, so do all tests.

Last futzed with by DannoXYZ; July 8th, 2018 at 09:16 PM.
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Old July 4th, 2018, 06:02 PM   #3
DirtyMike
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Hi thanks for the help. I was able to test the fan and it appears the fan works fine. Coolant is at the right level. Gauge still doesn't seem to be moving in guessing it has to be an electrical issue with the grounding or the thermostat itself?
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Old July 4th, 2018, 07:05 PM   #4
DannoXYZ
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MOTY - 2018, MOTM - Nov '17
Updated my post with specific tests. You've done #6, so we can skip that. Do others in order. There are several independent systems involved here:

1. gauge + temp-sensor - purely for human consumption. Doesn't affect thermostat or fan operation in any way. You can remove gauge+sensor, the thermostat and fan will operated as intended.

2. thermostat - controls physical water-temps via radiator. Doesn't have anything to do with gauge or fan. You can remove gauge+sensor and fan, and thermostat will still operate as designed.

3. fan & thermoswitch - control air-flow through radiator. Doesn't depend on gauge+sensor or thermostat to do its job. Which is just to turn ON fan at certain water-temp and turn OFF fan as water-temp drops. The spread between OFF and ON temps is to prevent rapid ON/OFF cycling of fan at transition temperatures. On many racing-bikes, fan and switch are removed to save weight.
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Old July 8th, 2018, 06:10 PM   #5
DirtyMike
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Thanks for your instructions! They were awesome. Everything was in working order - I think my diaphragm just needed to be forced open because it hadn't been used in so long. Odd issue to have but it doesn't matter. It's all good now!
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Old July 8th, 2018, 09:18 PM   #6
DannoXYZ
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MOTY - 2018, MOTM - Nov '17
You're welcome! Yeah, yours and model after (pre-gen) have really low-temp thermostats and gives impression it's not doing anything. Really have to ride bike hard to get up to temperature.
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