Oh and also I would advise against a pressure test in the system
Mainly due to the fact it could cause a lot more damage

A lot if radiator shops do it
To open leaks up more so you have to buy a new water pump radiator etc when you really did not need it.

Just a thiught

Gatesys by disconnecting the "plug" for the thermo switch (driver side radiator tank) that should keep the fans on 100% with ignition on. I found this info handy.

Update .... spent the whole day bleeding the system. and just to make 100% sure I did both methods, idle for several mins etc etc .... went for a test... all was good ... boosted up a few hills as a minor strain test ... idled fine etc etc no jump in temp .... ok time for more strain... went and "cut sick" for probably all of 30 seconds in the form of a couple of doughnuts to get the turbo working and strain the engine some... got down the road ... temp jumped again... took extra notice that thermo's did not come on... jammed on the heater full blast as I slowly accelerated (slowly to prevent boosting) temp came back down slowly at first then from 3/4 to 1/2 very rapidly, also noticed a fluctuation of heat in the heater itself... only water to escape was from the overflow bottle... heater on whole way home (not far) and temp stayed normal, but jumped up higher as I got closer to home.
 
Surely with the amount of coolant in the system not having the thermo's kick in wouldn't make the temp rise extremely quickly.
 
Unsure what to think now, as it only seems to happen under fairly high boost (11lb) I am leaning toward a slight crack in the head. On top of a buggered thermo-fan switch, and with the fluctuation in temp for the heater, I have not noticed if the heater is mixed in with the thermostat cycle, or if the change in temp is just due to bubbles as the coolant was boiling.
 
Might just park it for the mean time until I get a new switch, and thermostat.
 
Will also try a compression test in the meantime.
 
And cross my fingers it has not done a head.

no no, only realised for sure that the switch was gone after it heated up this time. that was when I pulled the plug on them.

not so easy fix ... bleed again today, unplugged thermo's so they on... still heated up. FML ... oh well ... Ill just have to drive the N/A around for a bit. no biggy.

I wouldn't think so, I am fairly certain that I have warped / cracked head or blown head gasket. just going to park it until a few bits and pieces arrive, then I will test further, before I strip it down. If it does come down to stripping her down though I think I will get some head work done, and possibly some cams too... turn a negative into a positive.

I sell heaps of the Cargo seal "seal up" but I would say both are a band aid fix...

I wouldn't put any of that chemical fix in a bottle stuff in my MR2's cooling system. Its likely to cause some other long term harm to something else like a heater core or radiator.
 
My recommendation would be to just get it fixed properly.
 
I would try the chemical stuff in a $1000 s-box though.