Didnt up going to CC due to some cooling issues i had with the car a couple days prior.
 
Heres the story:
On friday i went to my exhaust shop to re-enforce my exhaust muffler hangers as they have broken twice. I got them to make strong hangers with good welds. As i was driving home i noticed my water temps much higher than normal. I pulled over straight away. The oem gauge and aftermarket gauage showed hot temps, i opened the engine lid sitting in my car worrying what was wrong :(
 
I limped home, thank god i lived 10 minutes from the exhaust shop, pulling over multiple times to let it cool down. I noticed one of the many times i started the car back up my temps would drop, drop very quick back to normal temps (80 degrees) in a span of 3-4 seconds. I was shocked and confused how coolant can drastically change temps that much. So i was curious... are my sensors broken? both my aftermarket and oem one?
 
After i got home i started researching as this was my first experience with a cooling system issue. And learnt alot about the cooling system and only a few possible factors that could be at fault.
 
Drove it all day friday, saturday and sunday with no major problems. Keeping a close eye on the water temps, it was abit jumpy around 80 degrees but not enough to pull over. I was confused what was wrong... and it seemed like the symptoms of air in the system. My expansion bottle appeared to be empty which wasnt helping... [link=mailto:SW@)]SW[/link]20 bottles are so hard to see if there is any coolant..
 
I attempted to burp the cooling system: Just by removing the radiator cap and running the car over 80ish degrees to open up the thermostat and heater on the hottest setting. Leaving the car and revving it abit as well. Being new to burping the system this is not the correct way to do it.
 
On Monday night i took it a spin around the block and it started overheating straight away and i took it stragiht home. Strangely enough my aftermarket temp sensor didnt get a reading and my heater was cold!? I was thinking no way the water pump went! The radiator fans werent on too....
 
I started researching more and found the correct way to burp the system for air. I also was advised to changed to thermostat if it was the problem as they are quite cheap to do. (Luckily the thermostat is not the hardest thing to get to in the car)
 
I purcahsed a new oem thermostat and O ring for the car to rule it out.
GEN2 and GEN3 3sgte have different thermostats FYI the gen3 is slightly larger in diameter
 
GEN2 Part #90916-03075
GEN3 Part #90916-03100
 

 
Swapped out the thermostat. And them also tested the thermostat if it was working. Yes the old one was working fine. But i changed it out anything to rule it out completely. Also found out i was running a TRD 71 degree thermostat :)
 
Issue still occurred so i burped the system for air
 
Correct way to burp the SW20 system.
I changed the method slightly by doing one bleeder at a time.
Opening up the heater core bleeder until there was no air (in my experience there was lots of air here and the coolant was not rising up the hose at all....)
Then the radiator bleeder until there is no air
Then lastly the radiator cap. Then half turn it closed and go for a drive to move remaining air if there is any out. Then just close up the cap.
Keep in mind topping off the coolant when necessary 
Link: http://www.lovehorsepower.com/MR2_Docs/mr2_bleeding_cooling_system.htm
 
I did all and it was still overheating...
 
My friend advised me that the system might be clogged/stuck. He said to run the car and touch the radiator hoses which can be reached at the front. With the car >80 degrees both sides of the radiator hoses were cold. 
 
FYI the passenger side radiator hose is going into the radiator
and the driver side is leaving the radiator.
 
I was worried that my water pump went... but was advised i should flush out the whole cooling system to rule out for anything clogged.
 
Bought my
- Nulon concentrated coolant (whole system needs around 6-7L?)
- De mineralised water
- Radiator Flush

Link: http://www.nulon.com.au/products/Cooling_Systems/Radiator_Flush_and_Clean/#.UzQPbMszHqA
 
 
Flushing out the whole coolant
1. undo the drain plug on the radiator drain that out (this is on the driver side)
2. undo the two coolant pipes underneath the car and let that drain out. (in my situation, nothing came out... i was puzzled... it just meant there was big air bubbles in my system)
3. undo the radiator cap and have the garden hose ready and put it in the radiator cap hole
 
4. most of the water should be coming out from the passenger side drain hole under the car. Once you are satisfied that its clear do it up
5. I hosed it again and then the driver side drain hose under the car starts flushing out with water. Once you are satisfied it is clean and its clear water with no coolant coming out close it up
6. hose it from the radiator again till its clear water at the radiator drain hole
7. do up the radiator drain plug
8. start filling it up the car up with coolant.
9. Burp the system for air.
 
Doing this whole step my car is running fine now with no issues. Im just glad the water pump didnt go, cause that seemed his a bitch to get to and replace. Think the issue was related to air in the system.
 
OEM Thermostat:

 
Thermostat is out:

 
 
Air bubbles from radiator bleeder

 
Heater and radiator bleeder hose setup:

 
Car:

 
And unrelated bought a black finish single din 52mm housing for my gauges:

Have you checked for sign of slow leaks throughout the entire system.  Heater pipes at the back of the tunnel are a common leak point.

ps- get rid of that green coolant and use the genuine toyota coolant please...........

MR2QIK
 
Hopefully.....the overheating is gone. Most of my nightmares began with overheating.

so did mine, and ill say thats lots of others would have been in that same boat..

We were talking along the lines of flushing it out one day & replacing with red.
 
If you still end up with overheating issues, it's unlikely related to the green coolant though.

purple5ive
if the outgoing hose from the radiator is cold/ flexing that means theres no coolant going out from the radiator, which also means the radiator has air in it, which also means cooling fans wont come on...

In my situation both hoses were cold, the radiator fans did not turn on when it should of.
When i undid the radiator drain valve/plug i heard lots of bubbles moving around in the radiator before coolant came out.  Yet to see evidence of any leaks on my garage floor or underpanels when i was draining it
 

purple5ive
bleeding the MR2 is the most painfull and time consuming tasks ever. make sure you take the time and do it properly, if you think your done then drive it around and keep constantly checking the OVERFILL bottle, do not open the coolant cap (unless the car engine is stone cold/overnight scenario)

Ive marked the overfill bottle just then and ill keep it a close eye on it if it lowers
 

purple5ive
if you open when its warm etc the coolant will get sucked back into the engine (rather than draw from the over flow tank)

Sorry man, dumb question but can you explain how coolant will get sucked back into the engine if i open the radiator cap when its warn (car not running)?

Rico
Firstly, this a fantastic detailed write up on your cooling issues. Far better writing than I could achieve!
 
There is a very good reason for the use of the green coolant. That coolant (the green coolant) is what is required for motorsport. Rory built the car with trackday's being the priority then street driving secondary. It is a CAMS requirement that red coolant is not used due to its properties when you drop coolant on the circuit it provides more slip than oil. It is closer to sliding on diesel. I know this after a BMW dropped its coolant line on entry to turn three at Eastern Creek. I had zero grip mid corner and ended up in the dirt at 100km/h instead of being on the track. This was caused by using red coolant as opposed to the green coolant which does not have the properties which create this risk. As you enjoy going to trackday's, for the benefit of your friends I recommend you stick with the green coolant. The green coolant is also more effective at temperature control. any circuit racer/trackday warrior will attest to this.
 
EVO65 (quickest SW20 at Eastern creek) and Highlander(2GR-FE V6, ex Colin Osbourne Production Sports car)  had a lot of temperature control issues. This was solved by replacing the radiator. If you still have the standard unit, it may be worth looking at this or removing and flushing it.    
 
 

Regardless of what anyone says the factory (red in this case) coolant is what you should be using as it has the correct properties for the actual metals being used in the engine. Whilst the non genuine coolant will say on the bottle compatible with cast iron blocks and aluminium cylinder heads it does not mean it will work as well as the factory stuff. 
 
With regards to the BMW comment Steve that is very weird since BMW coolant is a blue/green colour, and certainly when i have some on the floor it feels just as slippery as the red Toyota of even red Holden coolant.
 
If a BMW uses the wrong coolant is causes all sorts of nastiness in a already fragile system (German cars use quite a high coolant pressure in a sealed system compared to a Japanese car and that is why you get spectacular explosions when you have a small leak)