I know these engines just shouldn’t get hot or they’re done for.
But I took mine for a half hour rip around tonight, pushed it quite hard. Temp looked fine, I then got back into the town, a few traffic lights etc and the temp crept up a bit. See red line on picture below.
I got home and the temp sat around the red line in the pic. But the fan was kicking in and didnt go higher.
I turned it off and immediately back on and the temp went back to the middle. Drove it around for 10 mins again and temp stayed perfect, then idled for another 10 and it didn’t move from centre.
Any ideas?? Or normal? Should I let the temp get that high?
Thanks 
Has someone linearised that guage. Normally they are dampened to sit in the middle, then swing over to the right when things get very hot. With a linearised gage, which involves soldering a resistor, the gauge is “true”, and you will see the engine run a bit hot at times.
However, check when the fan is kicking in, it actually is spining properly; the bushes on the motor can wear.
Check the expansion tank and radiator level; obvious really. A failing radiator cap can lead to loss of coolant from the expansion tank.
The 1.6 can have an issue with a blocked thermostat bypass line; on the thermostat housing there is a small line that allows a little bit of coolant to bypass the thermostat. When it blocks, the car can run hot at speed (and the fan runs more than usual). One reason it can block up is small pieces of metal, from when the head was originally made, work their way around.
Ok great, Thank you. It’s always been fine until today which is weird.
I took it out again just now and it didn’t go above 12 o’clock, although. It was sitting at 11 o’clock until I stopped for a while, then went to 12 and stayed there. Even at idle for a while.
Hmmm
How will I tell if it’s linearised? It does seem to move quickly. When the fan kicks in, you can see it move straight away
I had a guage on a 1991 Roadster linearised years ago. As I recall, from cold, you could see the gauge rise, and then spot the moment when the thermostat opened, allowing a slug of cooler water.
In terms of how to visually identify a modified gauge, I think these days there are some other ways. I used this approach:
http://web.archive.org/web/20040621122819/http://www.gravitydesign.net/saturn/miata/90-93MTGLP.cfm
So some resistors and diodes are replaced/messed about a bit, and some circuitry on the circuit board scraped away
At first, it took me a while to get used to it, with a gauge moving around all the time. Funnily enough, that car was red…
In 2001-2002, it was a pretty ppular mod.
Just taken a quick video of the coolant dial, jumping around just above the middle. Didn’t get hotter than and it only creeps up from 11:30 (if it were a clock) once I stop. Can’t upload it but the dial gets just above 12 then fluctuates between 12:00 and 13:00 every few seconds.
Fan seems to be kicking in fine too.
Faulty sensor? or just linearised?
Fluctuating every few seconds sounds like a bad connection or maybe a failing sensor rather than anything else. A linearised gauge drifts up and down, but doesn’t jump quickly or frequently. First thing I would try is to reseat the connector on the sensor itself.
Ok cool, I will do that later, thank you for the tip!
Does make sense, it seems to jump a few degrees every few seconds, but weirdly only when stationary!
Thanks
