Help FZR250 Temp gauge rises when lights are turned on?

I'm was confident I had it topped all the way up. When I changed the thermostat housing I completely drained it, keeping the coolant that came out because it is clean and green. I then had to rock it back and forth while it was slightly warmed up and as you say burp it by squeezing all the hoses. Yeah I noticed the frame/coolant line - I have the same concern about rust blocking the radiator, it might explain why when I rev it the temp gauge fluctuates as though the extra impeller speed could push coolant through...maybe
Would you recommend I remove the radiator and give it a flush with the hose or shall I buy some radiator flush and flush the system? Is there a decent home made radiator flush? Just a pain to buy anything during level 3 atm.
Also is there an exact coolant amount the 2KR's take? I believe the engine code is 1hx or 3hx or 1hx-3.
I just checking the courier tracking for my infrared thermometer and will be here very soon so hopefully after my call out I can have a play with my bike.
Thank you!

 

Ahh no I didn't realise there were 2 drain plugs on the cylinders... thanks @GreyImport and @ruckusman So check water pump(just the top cover off to check) drain plugs to bleed it, radiator flush, check instrument cluster, check temps with infrared thermometer - something of that order. I feel removing the radiator wouldn't go amiss. With the thermometer shall I check the temps at the radiator inlet and exit, same with all hoses etc?
Off to the plumb for now hopefully I have the time today to do everything but will check in tonight thanks everyone

 

Haven’t found any stray earth wires for the thermostat housing. Am about to take the front fairing off to measure current at the gauge. Just wondering, the fan switch on the thermostat housing has been disconnected and wired into a switch on the dash - would the earth be from those two wires and what way round on the fan switch do I connect it, does it matter?
There has been extra indicator lights fitted to the tail would this have any affect?

 

I also noticed there’s a bolt missing from the bottom of one of the coil packs.

 

So just measured the power to the instrument cluster and with light and off reads around 14volts and lights on drops to 10volts. Is that normal?

 

Yup always done with the engine running, haven't thought to try with it off. So the voltage at the battery dropped from 14volts to 12+volts. I'll definitely open the cluster up tomorrow and cleaning all contacts, with crc556?
That makes sense why they would've installed that fan switch - I did run an earth wire from the thermostat housing direct to battery negative and made no difference.
So I would expect the resistance to be the same or slightly higher from the sensor and then through the wire to the gauge? I'm assuming the higher the temp the less the resistance, but, will confirm that tomorrow.

I do have a spare thermostat housing which I've installed an aftermarket sensor into with an aftermarket temp gauge, would you say hooking that up temporarily would be a wise idea?
I feel it'll eliminate the electrical issue I'm getting with the current gauge and will tell me exactly what temperature it's getting to.

My infrared thermometer arrived today so I took some readings all over the cooling system hoses etc, all appeared consistent.
The ones of most interest is the radiator inlet and outlet which you'll see in the photos below.(BTW I don't know which way the cooling runs I can imagine from the top of the radiator down?

Lights on:


Lights off:


Radiator inlet:


Radiator outlet:


I took readings again after it sat idling for a while and the gauge was almost in the red with lights on and the thermometer readings were only a couple degrees higher.

 

That’ll be great @ruckusman @GreyImport. Yeah thermostat opens at 82C. No offence taken@jmw76 the more I dig the more I want to rebuild the whole bike but that won’t be for a couple years. I’m leaning towards bad earthing too, this evening I pulled the front end off and had a look at the dash cluster - looks like new to be honest. I swapped out the temp gauge for an aftermarket unit just to see if the temp jumps with lights and sure enough it does. Got me thinking though, the PO has installed extra indicator lights on the tail. I was looking at the wires used and pretty sure they’re supposed to be earthing to the frame. It’s my next idea anyway so will take some photos of it tomorrow and try figure out where they originally went - my guess is they’re from the tail light ground.
Here’s the instrument cluster, clean and corrosion free:


And the aftermarket gauge:

The gauge uses a different sensor so it was over reading but still jumped when I turned the lights on.