Ok so today I was refilling/bleeding/flushing the cooling system as it was a bit rusty. Procedure was done properly. I am not a novice anymore when it comes to the cooling system 
Anyways cutting to the chase I drove the car around to give it a nice flush, temp gauge started creeping over halfway so I pulled over. Waited about 5-10 mins. Drove again for 30mins+ no problems. Drained and filled system again. Same thing happens again, it overheats (or tries to) and I let it cool off for 5-10 mins, drove it hard again no problems.
The 2nd time I pulled over, I touched the radiator and it was cold. I suspect the same when it happened the first time. Drained water wasn't very clean which is no surprise since I recently had the engine swapped (import engine). So I have a few propositions:

• Dodgy thermostat? But it was recently changed...
• Too much rust, preventing thermostat doing it's job?

I'm thinking of taking out the thermostat and then blasting the engine coolant filler neck as I presume most of the rust is from the block. Hopefully it's not too hard of a job...
 
Background info (kinda relevant)
The engine was swapped by a semi-incompetent mechanic so the water plumbing may be sub optimal. (2nd Gen 3SGE to Beams from FWD). Another mechanic told me that the radiator wasn't getting warm, as I've now experienced. Since the swap completed I haven't had any overheating issues with the cooling but sometimes it would spike to red indicating air bubbles and temp gauge would actually go down at WOT with high speed. This has prompted me to service the car and of course everything begins to play up when you decide to touch it...
 
Long post but you know me (or have now) so I make no apologies lol
Any suggestions just yell out, much appreciated :)

sounds a lot like  somewhere in d system is blocked, more so a blocked radiator, get it reconditioned or get them aluminum unit that everyone gets

Out of interest what thermostat have you got in it brandwise?

Prob flush again before spending any more money.  unplug the taps at the radiator and then just hose through from the filler neck for a while until it flows clear.  Run it on just water for a bit so you can judge the rust/colour difference, then flush again.
Symptoms so far all match air locks in the system.  It takes a fair wack for the radiator to get hot but they should at least get warm.  Whether or not your heater gets hot will also help indicate how it's going.

Ahh I'm such an idiot...I meant to say ENGINE filler neck as that is where most of the rust is coming from, which would make more sense as it was an import engine (lying around in the import yard, weather corrosion etc
The radiator is very new, only few months old as I replaced it in Feb this year so it's clean as evident from my bleed tap. It's an eBay special twin core aluminium.
Thermostat was changed by mechanic so i'm not sure but I might check it tomorrow. Was changed by a good mech, not the same guy who fitted my engine.
There's no more air locks (no erratic temps, just steady rises) I'm confident but yes there was previously. Yeh I think I'm gonna blast the filler neck without the thermostat, may as well test it so see if it's working properly too. 
Good thing it's not a hard job, just time consuming so def save a bit of $$$ from DIY

 
I'm thinking of taking out the thermostat and then blasting the engine coolant filler neck as I presume most of the rust is from the block. Hopefully it's not too hard of a job...


looks like ur on the right track here then,
yeah test that thermostat. out of interest did the motor feel like its overheating? chugging/loss of power etc etc?? or was the temp gauge the only indication of overheating? i had 3 coolant sensors that **** itself on me(tridon super cheap stuff) giving false readings, so i decided to get a genuine toyota sensor never had a problem since

Make sure  your running a genuine Toyota thermostat as well. The aftermarket ones are ****e and don't work well.

You can tes tthe thermostat after you take it out aswell by dumping it in a bowl of boiling water and seeing if it opens up. You can even test it at different water temps to see when it is opening.

Radiator cool means no coolant going through, so the first thing to do is to  test thermostat in the way suggested to eliminate that possibility.
Make sure the jiggle/rivet is facing upwards when installed.
 
If the temp gauge is going past the middle, I would not be surprised if there is still air in the system.
I'm sure you know bleeding properly takes a lot  time and patience with these cars, and is vital.
 
 
 
 

Oh man I just looked at the thermostat housing position using a mirror, it's right below my alternator FML. My alternator is in the Celica/Caldina position btw for easier change in future. I'll try see if I can do it under the car...
Didn't really feel any loss of power, maybe idle changed I don't really know as my tacho doesn't work haha (what even works in this car...). Lucky the Beams only has one sensor for temperature apparently :D
I've tried Tridon in the past with my last engine has no problems.
I'll take note of the jiggle when installing
Thanks for the help so far guys!