If you do decide to change it, I personally would get a genuine thermostat and gasket. You can order it from Toyota and it will only cost $16.78 + $5.37 for the gasket, amayama was about $35.00 and ebay even more.

I was wondering why it was so expensive on ebay, and yeah you usually need a gasket I forgot that, they go hard and usually crack when you open it up.
 
Also I remembered why they have a small hole in them, it's to let the coolant flow a small amount so it doesn't get heat locked inside the engine and boil.

Just saying, that thermostat you linked looks really odd - maybe it's a different kind of thermostat? I linked the Autobarn one earlier, I'm pretty sure they're meant to look like that - with the 2pin connector and just a bar-shaped sensor, like a MAF. 

I watched this video on YouTube of a guy pulling the same sensor out of a Camry and it looks the same as the one I linked earlier: https://youtu.be/r8gGN5YTDzs?t=164

Edit: That is a good point regarding the gasket, I'm consulting my 3S-GE repair guide now and it states the gasket is not re-usable. I'll have to get in touch with my local Toyota dealer for a price quote.. does anyone know the part numbers at all? My local dealer is hopeless when trying to interpret parts.. I had to physically show them the targa carpet "mounting knob" (surely everyone gets what I mean by that) I needed a replacement of to get a quote, even after explaining it as thoroughly I could over the phone haha

Also finally found the table.. sucks my PDF version of the manual doesn't have a search function, had to scroll page after page to find it haha. So I'm not the brightest tool in the shed - I want to test the resistance from cold, make sure it meets 10 - 20 kiloOhms then as the car warms up, the resistance should diminish? 

Also how would I test it? Just the positive probe into the back of the positive pin/negastive into the back of the negative pin?

Oh I've had a lot of success identifying parts using http://toyotamarket.ru/jp/
It's actually really good, give it a go, let me know if you can't figure it out.
You can then order them on http://www.amayama.com/ by putting the part number in.
Be careful of prices on there though, some are cheap, some are... interesting, like a factory tape player costs over 2 grand :)
 
You are talking about the temperature sensor, I am talking about the thermostat. Two different things. The temperature sensor measures temperature and some wires hook up to it. The thermostat is a valve thing that goes INSIDE the coolant system. You have to unbolt the thermostat housing which is where the gasket is. It's a gasket about the size of a cricket ball. I'm pretty sure you need to drain the coolant to change the thermostat, because it's going to gush out everywhere otherwise.
 

You have to be careful testing resistance, you can't do it while it's connected. If you unplug it while it's running I think it will throw up an ECU fault code and possibly put it into "limp" mode, so I probably wouldn't do that. Nothing to stop you from running the engine until warm, then switching it off and quickly unplugging the cable to it and then measuring the resistance. Just don't measure resistance where there's 12v power.
 
The other way I mentioned is to set your multimeter to volts mode (usually 20 volts for a car) and get a voltage from it. Don't stress about where you stick a digital volt meter, you can practically put the two probes anywhere without upsetting anything as digital voltmeters have a huge resistance, they don't really appear as anything to a circuit.
 
To get some sort of information out of it though, you'll need to figure out the reference voltage MR2s send to the sensor. I would guess they send 12v, but don't quote me. Then apply ohms law and you can figure out the resistance.
 
Does it have two wires going to it or one wire? If it's got two wires then hopefully one wire will read 12v and the other wire will read the output of the sensor. It's kind of hard to explain it all, to measure the voltage of each wire you put one lead on the terminal and the other lead on ground somewhere, usually right where the sensor screws in.
 
Hope that makes sense.
 
 
 

Oh, touchè. Didn't realize we were saying different words haha
I get what the thermostat is - for some reason I was mixing it up with the sensor. 

Hm, the thermostat seems like a much bigger job. I was keen to replace the sensor as I figured it'd be a simple easy fix. The actual thermostat valve on the other hand probably won't be, as I've never bled the cooling system before so that'll be new to me.. hope it's not too hard of a task

I'm guessing my best course of action for now would be to do a resistance test on the sensor (using the method I said before I think), see if that needs replacing and if not, I guess it's time to replace the thermostat

Edit: Just thought I'd correct myself and say I'm an idiot for thinking of testing resistance with power running - I was studying to be a sparky (only for a few months however) and I should know that that will end up with a blow multimeter in my hands haha

As for testing the sensor in voltage, I didn't think that would work. Wouldn't the sensor be receiving a DC power supply, meaning that even if the sensor was faulty, it'd still receive the correct power? So I'd be getting the correct reading, but I wouldn't know if the sensor itself was working properly

So I went and took a look at my gen 2 JDM 3S-GTE engine, and the ECU temp sensor is indeed a two wire. I have no chance of fitting my hands and the multimeter probes in there so next best thing is to check it from the ECU terminals. Supposedly it's terminals C4 and C9, brown and red wires. Now I just had a look and it seems each different generation had different wiring to the ECU so I'll give it a go on mine supposedly a gen 2.

Had a look at where the thermo is on the 3S-GE. This doesn't look like a driveway job, may have to give this one to my mechanic. Which sucks, was keen to give it a go

But the positioning of the thermostat is probably going to be impossible to reach without a hoist, so there will be heaps of mucking around to get this done. Damn thing..

Edit: You are right, I'm pretty sure every Generation of the 3S engines had their own ECU wiring (for some reason)

Edit 2: I've read quite a few threads and a lot of people are saying there's no need to drain all the coolant. Just hose off, take off old housing and thermo, new thermo/gasket in, make sure jiggle valve is aligned properly, housing then hose back on. I'll still need to bleed it though.. apparently that's not too hard but I am a Gumby

Mine was 741 ohms which was about 50 degrees according to your chart. About right since it was cooled off from driving a coupe of hours ago. I tried getting voltages but failed, I'll have to play with that some other time.
 

Hoonsy
Also how would I test it? Just the positive probe into the back of the positive pin/negastive into the back of the negative pin?

 
I couldn't fit my hands in there so I unplugged the C connector of the ECU (the middle one) and stuck the multimeter across red and brown according to my pinout here: http://imgur.com/6hGuEOc
 
Edit: forgot to mention my ECU was getting a battery in voltage of 10v :/ might have to check that out some time, I might have some dodgy wiring as mentioned in another post I read where the early gen wiring harnesses had corrosion to the ECU.