overheating issue wierd

Update .... couldn't be thermostat, as while driving / cruising ... it will stay constant, normal operating temperature, only heats up while idle, pulled the plug on the Thermo-fan switch leaving them on as a constant to get me home.
 
Starting to fear the worst and think it may be a warped head, turbo spools, push's air into the cooling system ... after a while it would create enough of a bubble to heat.
 
Anyone got any tricks to test this before I decide to pull the head off?...

Had several cars before that have blown heads etc and no water in oil etc, the water pump I used was a GMC, same that came out.
 
Bleeding of the system may be overlooking something?... did seem a touch odd with the 2 bleeder hoses up they did not seem to be at the same level ... close though... also, ever so slowly it does seem to drink the water.. so air in the system may be the key ..
 
I have tried the 3 minute idle with both bleeders shut off, and both open, both times with radiator on one click.
 
Have also tried filling up the filler cap .. and releasing water from the bottom of the radiator recap, top up and open bleeder again (to pull excess air from the lines).
 
The other thing is that it seems to take a little time before it starts happening, like 20mins or so..

Could be worth a look into, but I am sure I would at least see drips while either at idle, or right after it was turned off, I've watched it meticulously during the "test" I performed, may try that simply to eliminate that as a problem though, cheers.
 

"the water pump I used was a GMC, same that came out".
What is a GMC???
Some aftermarket pump inserts have smaller vanes than the OEM ones so it is always recommended to use genuine Toyota replacements.
 
"ever so slowly it does seem to drink the water, so air in the system may be the key".It does seem suggest that air is still in the system.
Patience is needed with MR2's and it is not uncommon to have to top up for a week or so after refilling the system.
 
"did seem a touch odd with the 2 bleeder hoses up they did not seem to be at the same level"..
I have found that if air is still in the heater, the level can be lower in it's bleeder hose until it is purged out.
 
BTW, have you tried feeling the pipes in the frunk to monitor the coolant temp in and out of the radiator. Could tell you if the coolant is circulating ok.
 
 

do a pressure test on the cooling system. That way you will find out hidden leaks. Mine only leaked after 10mins of testing and it was very little. Turned out to be a cracked block near the waterpump area

Might grab a few bits n pieces tomorrow to make a pressure "Plug" for the filler cap, anyone know a good pressure to throw into it?... don't exactly want to bust any pipes / radiator cores. ... leave it plugged up over an hour or so and see if there's any change...
 
All good ideas though, Hoping there is no major damage, but all was working pretty well just before I changed the water pump.
 
#Redtarga, there shouldn't be a problem with the GMC water pump as it was the exact same one that I pulled out to replace it with, and was working 100% before, only changed it because the inner seal wore out. Started leaking through the tell-tale hole.
 
I have checked the Radiator lines, before removing the thermostat on a test run after changing the water pump, it did get hot with radiator lines staying stone cold (down the road) heated up ... then quickly went back to normal, got home, and radiator lines where warm (operating temp)
This was one of the first things I checked as soon as I pulled up, and yes they where warm. 
 
I am thinking there may still be a few pockets of air, possibly gathering in the return radiator tank preventing the thermo switch from being activated, and leaving the fans to stay off. Have had this happen not too long ago, rebleed and all was good again.... fun fun times...

I would make sure your thermo fans work properly

Because mine stopped working and it would overheat

This was the turbo one
So what I did checked relays then the switch all had power

So I decided to bleed the system did it for a solid 20 - 30 mins

Both clear hoses up front on the bleeders held above the filler neck so the air rises
Pressure cap off
Idle till warm

Continue topping up filler to top of neck
Water in the hoses should not rise above filler neck

Lots of bubbles from filler neck and clear lines

Close bleeders pressure cap on first click
Held at 2-3000 rpm whilst brother rocked the car
For a few minutes opened bleeders
Lots of air and bubbles
Opened pressure cap continued topping up

And rinse and repeat

Towards the end my fans started working again (huzzah)

Not an issue since
Knew it wasn't a head or gasket issue as my comp readings were spot on

But I also was boiling coolant

I will almost gurantee it's air in the system

Also not sure if yours is turbo or not
But if it is
May well be the hose from hell

But other then that could be a crap water pump or thermostat
Any toyota should keep thermostats on the shelf
As there the same used in many other toyotas

And also tree is right aswell I was just saying in a severe case

The head being warped I highly doubt.

Start with the easy stuff
Never heard if a bleeder near the gearbox?
I thought that was a drain point, I thought it had 3 bleed points
2 up front
Then the pressure cap/filler neck

Good luck :)