Fazer fzs1000 radiator fan problem

[steven_191]

Morning all, long time since I've logged in!

I have an issue with my rad fan. I've just been on a track day and at the end of the day noticed the fan wasn't running. I've commuted since and still haven't seen it run.

I did the necessary checks but still can't work it out.

Fuse OK, relay proved, fan does run. I got down to the thermo unit. If I unplug it and short out the plug the fan starts. I thought this means the thermo unit is the issue. I replaced it but still no luck. I believe the circuit goes through the clocks but I feel like I've already proved the circuit by shorting the plug.

My only other thought is that the plug could be an issue, or the circuit is the problem and possibly a high resistance joint somewhere. So when I short it out I'm actually dropping the resistance enough to get the fan to run?

I don't know. I haven't blown a head gasket so can't be that bad right??

I've read that the fan should start after idling then shut down when you go into gear but that doesn't happen either. So could be the clocks again if that's where the control is coming from?

Cheers!

[Andy_Pagin]

My FZ1S has two fans and two fuses, one per fan.
I had fan a problem with my 600 Fox-eye Fazer that was down to the thermo switch. While I was waiting for the part I bodged a handlebar mounted manual fan switch, worth a go until you get to the bottom of it.

Is the rad fully topped up? Could be the thermo switch isn't getting wet?
____________________
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Yamaha Vity -> YBR125 -> FZS600 Fazer -> FZ1-S Fazer

[steven_191]

Yes it's full up. I can override it by shorting across the plug. This is where I'm now getting stuck because it would suggest everything else is OK.
Obviously the new thermo switch could be a problem......

[steven_191]

I did a bit more testing yesterday. I checked the resistance across the thermo unit at the thermo unit pins and it read fine and the resistance changed fine. I also checked the resistance at the plug in the clocks although I only remember doing that when the engine was cold to compare reading including the wiring loom and everything was fine.
I did resistance tests on as much of the wiring as I could and I can't find any problems.
I shorted the ground from the fan relay to the battery and it turns the fan on, simulating what the bike should be doing.
While messing about I was letting the bike idle. It was getting quite hot and I plugged the thermo unit back in. The overheat light came on and the fan started. I let it run for a minute then turned the bike off. It all seemed fine. I started the bike again after letting it cool for a while then no fan again.
This made me think that the sensor reading is responsible for starting the fan and also the overheat light. Which doesn't seem like a good idea as a failed sensor would mean no cooling and no indicator light, unless there's another reason the overheat light came on and that has the ability to override the normal cooling control. Either way, that control still comes from the clocks.
The sensor reading went down to around 1ohm which is what the manual says is just over 100degC, and shorting out the thermo unit plug still causes the fan to start. The thermo unit reading correctly suggests the flow is OK as the temperature changes correctly so I still don't think the stat is the issue. Everything gets hot so flow appears to be good through the header/stat/hoses.

The only thing I can think from here is the resistance across the thermo unit isn't dropping so I think I should get the bike hot then compare the reading between the thermo unit and then at the plug in the clocks to compare it including the loom.

If that's good then it must be the clocks?

I've run a parallel ground to the fan relay from an old heated grips switch so I can at least turn the fan on if the bike isn't moving.