I had this exact problem some years ago and turns out it was the head gasket. Replaced with new OEM gasket and havnt had problems since

 

What is the proper way to fully bleed the system?

 

i like to jack the car up in the front as high as you can helps get the radiator higher and use the bleed screw and don't forget to bleed heater circuit the rubber nipple on the firewall. i like to squeeze the radiator hoses then open the bleeder look up billman 250 he has a good write up. i have the same setup and in the winter i cover part of my radiator if its below 40 degrees as i over cool with a spoon thermostat, 170f switch and fullblown radiator so the intermittent heater says airin the system but if you saw 4-5 bars then a head gasket my be in your future

 

Get a leakdown test done and also update your coolant temp. calibration in your AEM.

 

don't you think a leak down test is a bit of an overkill for a over heating/possible head gasket issue?

 

What pressure is that cap rated at?

 

I've actually never heard of a block tester before but if it works it would be simpler.

 

I've actually never heard of a block tester before but if it works it would be simpler.
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If you're ever suspecting head gasket being an issue with your car you should look into it-just for future reference.
All you do is put this blue liquid into this tube with a small hand squeeze bump at the end, stick it into your radiator securely, drain some coolant out so it can't be sucked in, start the car for a few seconds and start squeezing, if the fluid changes color from the original blue, it shows that exhaust gases are being pushed into your radiator. (reads for carbon monoxide) which is an immediate sign for warped head or leaking head gasket. If the leak isn't too bad the color will change slowly.
Literally takes just a minute or two.
Just did mine a few days ago, changed color immediately, like within 1-2 seconds which is very very bad.

Edit: To OP: If you want to check for a leak and still don't want to try the block tester, you could try a pressure test, works by hooking up some compressed air into your radiator to about 15-17psi and seeing where coolant shoots out of.
If it loses pressure and you can't see any leaks, it's probably leaking internally. (Head gasket)

 

So I just did a compraition test and the number are:

- 210
- 210
- 189
- 189

I heard that they all should be around 240??

 

Every car is different but I guess ideally 240 would be that magic number. Well, I don't know, I've tried to help you as much as I could, not really listening sooooo I quit.
Best of luck, I'll check in case you do.