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Discussion Starter #1
My 2nd gen water temp went up to 248F then started flashing. The fan never came on. I limped home with multiple stops for cooldowns.

Later I tested the fan and it did work when I shorted the wires going to the fan thermo switch. I started the bike and it overheated again up to 235 before I shut it off. When I touched the radiator inlet and outlet tubes, the inlet tube was warm but the outlet was cold (so was the radiator itself). This could be a broken water pump, but I'm guessing not, just because I didn't see many posts on it.

When it overheated, the pressure did not vent from the cap - instead there was hissing/leaking in the area where the water connectors go into the engine.

Do I need to follow the manual steps of testing the thermo switch, the the coolant temperature sensor, and the thermostat? Does the hot radiator inlet hose mean the thermostat opened?
 

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If the rad is cold and the engine is hot there is only 2 possibilities, thermostat is stuck closed or waterpump isn't pumping. Easier to remove thermostat and see if waterpump circulates water. Then go from there.
 

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Discussion Starter #3 (Edited)
Is the water pump supposed to be pumping as long as the engine is running?
Edit: Yes. But I'm not going to reinstall w/out it. I'll try short circuiting the fan thermo switch next time it's hot. That probably won't work, in which case I'll disassemble and bench test the thermostat. Maybe it is barely opening, making the hose warm but not flowing enough to cool the engine.
 

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The fan isn't the problem, it's not turning on because the coolant where the temp sensor is isn't hot enough. I always drill a 1/8 bypass hole in the thermostat to bleed out any air in the system. Yes waterpump turns as long as engine is running.
 

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... When I touched the radiator inlet and outlet tubes, the inlet tube was warm but the outlet was cold (so was the radiator itself). This could be a broken water pump, but I'm guessing not, just because I didn't see many posts on it.
Has the clutch cover ever been removed on this bike? If so, it is easy to crack the water pump driven gear (plastic on 2000+ SV650) if not aligned properly during reassembly.

I agree with Svracer2, it is not the thermo switch, something is preventing coolant flow. Check low coolant, thermostat, blocked passage, or broken water pump/gear.
 

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Discussion Starter #7
Turned out that my coolant was low. Sorry for the lame ass question. After filling it, some coolant leaked from the water union (I think), so either that seal is bad or maybe the radiator cap isn't venting through the tube correctly and it is releasing at the weakest point. More items for my winter punchlist. Thanks everyone for the input.
 
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