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.

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

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

Hahaha I really like that reasoning! Thanks mods!

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 :)









 

Sorry to hear of your overheating issues.
I had exactly the same symptoms on my previous 3S-GTE engine after Mr T flushed my coolant.
Did all the things you've listed with no effect, ended up swapping in a Gen 3.
I highly suspect that the initial problem was compounded dramatically by me continuing to driving it around after the initial overheating event, (with one eye on the temp gauge and a hand ready to turn the heater on), to the point where only an engine rebuild or swap would solve the issue.
 
A couple things you may want to check;
Warm engine up with radiator cap off, do you see bubbles coming out the filler cap? If so it's probably the head gasket or trapped air in your pipes.
There is also a chemical test you can complete, that checks for engine gasses dissolved in your coolant, this would again indicate the head gasket or crack in the block.
I had my coolant system pressure checked, all was fine pressure wise... but I'm sure now that there was probably a micro crack in the block or warped head/head gasket which drove engine/coolant temps up.
 
I hope this helps and wish you luck with your MR2.
 
 

Hey DVSTurbo2 thanks for the advice I've stopped driving her since...yesterday
I did that chemical test you mentioned on Tuesday and it's all fine. When I drive the car hard after a warm up there's no probs at all. It's only during the first 20 mins of cold start but that's enough reason to not drive it.
It's all good now I've passed the stressful bit as I know what the problem is now. Just focusing on the positives like being grateful to have a car lol etc

Hopefully you can start to get some enjoyment out of your car.

Theres no shortage of us putting lots of $ for minor miles.