Leaking coolant from an unidentified part

If you unbolt that top part there is an o ring underneath. Fairly cheap from Toyota from memory.
Not worth doing a dodgy job with gasket goo etc.

http://www.mr2oc.com/showthread.php?t=597802

If you are fitting a new O ring or thermostat make sure the jiggle hole is facing the top, or it could be even harder to bleed the system than it is already.
 

That's the water neck coolant outlet, I literally did the exact same fix a couple of weeks back (mine was pissing out red though :P). Basically you just need to get the 2 bolts it sits on (be really careful mine didn't want to come and I did a few doses of WD40) and I think I undid a third to make it easier to get at, pulled off a few lines etc. About half a litre of fluid came out and then I just topped it back up and bled it, didn't get any bubbles and seems fine.
 
90301-40005 is the product number, the stock one has 6 bits around the inner circumference but I just used a thicker oring and put some of the goop on the oring (Couldn't be bothered waiting for the oem part to come in the mail), I did end up filing it a bit as it wouldn't go in quite properly at first. The oring that I pulled out was literally in pieces. Now the cowling underneath of my engine is not covered in red fluid which can only be a good thing. 

petmr2
My mechanic installed it so not sure if he did that... He said he bleeded the system properly... Correct me if I'm wrong, once I replace this o ring, I refill the coolant and leave the radiator cap off and then run the engine until it gets hot and watch air bubbles to come out of the radiator cap hole? How long before I know it's bleed pro[perly?

No!!
Before trying to bleed anything check out this:
http://www.mr2australia.c..r2play/tm.aspx?m=113820

I don't think the mechanic did this... I guess I'll have to bleed the system myself... I replaced the radiator (rusty) with a aluminium radiator from ebay so not sure if it has a bleed valve... Will bleeding it from the 2nd bleed valve in the frunk be sufficient? 
 
So for me to bleed it properly see as though the flushing bit has been done, I just need to get a hose and connect it to the bleed valve in the frunk.
Then raise the hose and start the engine? wait for the air to come out? How long do I let the engine run for? Until the fan kicks in? Do I then shut the engine off and watch for more air bubbles to come out? then when cool down top up coolant from the engine bay? Repeat as many times until no more air bubble?
 
I also read this on another article "Once the hoses up front are to the level of the rear pressure cap you can put the cap back on, and start up the car" Not sure what that means? how can you measure the front and rear?
 

I have aftermarket radiator with no bleed valve? Is that going going b b problem?