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Discussion Starter · #1 · (Edited)
(I don't know why I posted this here, as there's clearly a ZX750 subforum...sorry)

I finally registered here...hot damn!

Here's the deal. The cooling fan on my '90 ZX750 has decided to run all the time, even when the bike is off. I've resorted to pulling the fan fuse, but obviously that'll end up biting me when I hit traffic, which I shouldn't be doing anyway since I ended up totaling it (just because of fairing damage), so it's not registered, insured, or titled for road use. :p

I replaced the battery since it was basically dying every other day, and had a slight hope that it was messing with the fan...guess not.

The bike does this even after sitting for days. The ignition is either in the OFF position or OFF/LOCKED, and as soon as I connect the battery...Fan on.

Is this easy to figure out? Fan switch? Temperature sensor? Thermostat?

I'm leaning towards the first two, since the temperature gauge is functioning. The coolant is fresh and topped off.

Any help would be appreciated before I get screwed with labor charges at the shop.

EDIT: I received a reply from my shop and here's what he said...sounds reasonable:

Diagnosing the bike without looking at it I would say it is the fan switch. The water temperature sensor shouldn't be involved in the circuit for the fan. That would be a separate circuit only for the a gauge possibly. The fan switch has power running to it constantly and it will only trip with the inside of the switch heats up enough for the wax(or whatever substance is inside) to melt and provide a path to ground. Most likely the switch is bad and it provides a path to ground all the time. I would order the fan switch if you can't bring it in to be diagnosed. The price on the switch is $64.92. Let me know if I can order that for you
 

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I don't know anything zx750 specific but it sounds probable.

Real easy is to ohm the sensor out.

I had a coolant temp sensor go out after I crashed my 636 a few years back. Every time the fan tried coming on it would pop the fuse. Took me a few minutes to change it out and she was good to go!

Easy fix though, you should be able to install the sensor yourself if you are so inclined =-)
 

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Discussion Starter · #3 ·
Thanks for the reply.

I ended up taking it to the shop, since there's a problem with the charging system now, too. If it costs too much to fix, it's time to part this old thing out.
 

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Discussion Starter · #4 ·
The alternator/stator was bad, so I guess that was somehow screwing with the fan. All is well since replacing the stator.
 

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The alternator/stator was bad, so I guess that was somehow screwing with the fan. All is well since replacing the stator.
The charging system and the cooling fan circuit are separate circuits. The reason your fan was on was because a short to ground after the fan unit, most likely the thermostatic fan switch.
 

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Discussion Starter · #6 ·
Thanks for the clarification. That was the original guess, but nothing has gone wrong with it since the alternator was rebuilt. I'm sure it'll be acting up again at some point.
 

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definitely the switch on the side of the radiator that controls the fan...

simply unplug it to see if the fan turns off.. while unplugged, meter it out.. if the bike is dead cold and theres continuity, the switch is shorted.

also.. please, for the love of God, don't drive an unregisered/uninsured bike on public roads. i just spent almost 2 months in jail for that stupid shit. save yourself 2 months of missed freedom and shitty food. besides, p.a. will fine the shit out of you for that shit. i'm from pittsburgh.. i know..lol
 

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Discussion Starter · #8 ·
As I said before, since the alternator was fixed, the problem immediately went away. The fan operates as it should. I wonder if the weather had any impact on it, but likely not.

As to the illegality...I dropped it off at the salvage inspection station a week ago. :)

Of course, now I've gotta pay a sizable inspection fee, tax on the insurance payout, and new title, registration...blah..
 
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