how can the bypass hose be missing
wasnt your old engine running fine temp. wise ????
im also leaning towards the pump. should have used a genuine one man.

I think its a beams engine he has.  If it has its thermostat in the water pump inlet as normal with the other 3s engines and it does NOT for some idiotic reason have a bypass hose feeding heated coolant to the water pump inlet and consequently the thermostat then the thermostat will only ever open via conduction from the coolant in the block through the water pump.  Absolutely hopeless.  But it does fit the symtoms.  Must have a bypass hose from the coolant outlet on flywheel end of cylinder head to water pump inlet .   PM me if you need more.

Tree, have a look at this link and tell us if you have the bypass pipes pictured. It is a 3sgte but should be the same as yours.
http://turbomr2.com/MR2/H...lding_the_3SGTE-02.htm

Thanks for the concern fellas lol
I am a little weary about the dyno but I think it should be okay as long as I warm up the car before the run. At least I'll be getting the tacho fixed that morning lmao
It's dark outside so I'll take some quality photos tomorrow of my plumbing jobby.

Off topic but...I'm an MR2 Master now  loool seems to have happened after giving all the thumbs up. Ironic but as the saying goes "give and you shall receive" hehe

'master' probably means suffering great frustration and mastering the urge to set the thing alight!

Hahaha I really like that reasoning! Thanks mods!

im going head gasket.
 
when mine was screwed i used to find the temp would drop if i kept revs up to force water through.
 
by the time i actiually changed it , was too late, alloy head had gone soft and i had to get a new one.

I've been told the HG on the Beams is some tough metal, if it blows it'll be somewhere else like a hairline crack on the block.
Anyways positive results from the decay test! So HG is ruled out officially
I'm now 100% sure it's the bypass that's missing. This article explains it pretty well:
http://www.ehow.com/how_7...olant-bypass-hose.html
So my erratic temp gauge is due to "cavitation". Cool word. For now I'm just gonna stop driving the car until I can get it to IDB where they can do a proper plumbing job.
Oh yeh here's a few pics of my current Frankenstein setup:
Notice the weird looking outlet - that's the fwd water outlet from the Caldina/Celica. Most likely better if I change it to one from a Beams SW20 but even a Gen 3 3S from late model Sw20 should be okay. So if you see one for sale let me know :)









 

First pic shows that there is no clearance between the timing cover and strut tower :/
Once I get everything sorted out, I feel compelled to write up a definitive guide to the Beams swap in an SW20. I know it's not a hard swap but I know there are more fools out there like me knowingly making their life harder. As Gen 2s are getting older I suspect these engines will be a commonplace but I'm actually surprised they aren't common now!