Yea it's fairly high in the system about 10cm below the cap on what looks like a thermostat housing, however my system is bled so theoretically it shouldn't be an issue. I should mention the system has only done this on very hot days or very long drives, it did manage a Sydney to Newcastle trip just fine not too long ago but on the other occasion I got that hot reading. 

I  may clean the sensor plug just in case but I've managed to secure a cheap alloy radiator off an ex-forum member. The brand is Fenix, if this solves the problem I'll be happy, if not I won't be out of pocket $500 for a new one. 

Yea that sounds like a good idea anyway because I've never replaced it and they're as cheap as chips. Will report back once its been changed.

Yea going to get an OEM one they're $22. Problem is my engine is a Gen 2 but there are 2 thermostats in the catalog, they changed in Nov 1993. I'll probably get the later one seeing as there were gen 2 engines after this period but it is confusing haha, especially when they're rated at the same temperature  

Gen2 and Gen3 thermostats are different sizes. Gen3 is larger in diameter.
Gen3 part number is 90916-03100. Gen2 is 90916-03075.
I took a pic of both but can't find it at the moment.

Okay so update, the new radiator is in!

 
The hardest part was probably getting the hoses on but once you took off the cover in the frunk it was much easier to maneuver the hoses off

 
I then drove it around the block and it got quite hot because there was still air in the system, the radiator has a plug not a tap so I couldn't fit a hose to that bleed point, instead I drove it around the block,waited for it to cool, topped up the coolant then rinse and repeat a few times till I could drive it back from the workshop I had for the day. I will have to progressively keep filling the coolant for the next week more than likely. 
 
I was going to keep the old radiator but once I saw it I thought there's no real point given the state of it. 

 
NEW PROBLEM!
On the way home it ran cooler than normal which is good but pulling into the driveway the clutch wouldn't come all the way back up :( it would still engage but it couldn't come up on its own. This is a real pain as I replaced the master and slave only 12 months ago. I'm not entirely sure what to do. I'll likely take it to a shop and ask them to vacuum bleed the clutch as I can't think what else it could be. I checked the firewall and there are no apparent leaks, nor are there any from the clutch line at the back. 
 
 

If I do that then when I remove the hose air would just rush straight back in and I'm back at square 1? 

in terms of the radiator I took out the plug and when it spewed out coolant I quickly put the plug back in and have been topping the coolant up each day. It maintains a nice cool temp so that problem is solved.
 
The clutch however is a terrible problem. It won't bleed with a one way valve because there is always air in the pipe attached to the bleed screw and the same happens when I put a hand vac bleeder on. Despite building 60inHg in vacuum pressure it would not  suck fluid, it was as if air was getting in somewhere because the air didn't stop. Ended up just reverse bleeding it with a syringe and that was the best we got it. 
 
The problem is still there where the pedal go's to the floor (but not all the way because I can still engage the clutch) and I need to pull it back up. I tried changing the clevice and push rod on the master but even after setting it to have max resting pressure the problem still exists. Sometimes I can driver for 30min and it won't happen. Most mechanics and friends seem convinced its a faulty master :/