Capri has 13/90 cap and two types according to Repco. Overflow and non overflow and I've tried now both types new as their cheap. And yet green fluid spews out. All I think I can do is pull the heads and manifold. Hope I find the issue or it could be lower down in the block with dreaded core plug build up issues. F me it's time for rego which I'll do first then worry about it later. But even that may be an issue which out it leaking.

No not a constant steam of bubbles more like huge bubbles that overflow then needs topping up. Like it's burping gas really.

h

Essex engines need a thermostat, so get a new one and install it.  Factory autos have a radiator shroud, look out for one if you dont have one fitted.  I find the cooling system needs to be be bled with the heater on full, rad cap off until the thermostat opens, then top up and wait till the bubbles stop.
 
Your photos show the inspection cover in front of the fan is missing, this plays an important part so re fit it, or if its missing (like a LOT of capris) then chase one up
 
I have seen people mess up the hose order this will cause grief, check the location of your heater and carb hoses

Wiggy I'll freely admit my mechanical aptitude is way less than any aus male would  freely admit to , and I'm talking as a person who recently had to remove the thermostat housing again just to check I did not replace the thermostat upside down in the first place, but can I ask, from the above first post, did you end up replacing the thermostat after RACV did their mods?
 
I understand it probably should make bugger all difference, but it would suck if it was something simple...
 
 

thats a wierd one if gasket was blown and you tested it while engine was running it would of shown some sign of pressure loss within 30 min ,,gee thats a weird one ..
 
the only other thing i could think of if the pressure is holding is either some broken fins in the water pump or rusted out fins  that doesnt allow it to pump water thru the engine fully ..
 
certainly is a weird one
 
i think i have 2 new spare head gaskets laying around if you want to chuck them on might even have the manifold gasket as well ... there not the real good brand name ones but if you want to give it a go let me know and ill express them to you
 
cheers

Looks like you did some damage driving it for who knows how long and in what highway temperatures without a Radiator Cap which was invented to raise the boiling point of your coolant ?
Without this advantage of high boiling point for who knows how long (details are sparse), the water has expanded and overflowed (no cap to control nature), so less coolant and zero pressure to help engine stay cool results in a very overheated engine, prob not helped by a partially blocked & very overdue Major Flush by a Radiator Shop.........don't fool yself with chemicals: nothing beats tank removal and a thoro rod-gering of the core tubes by a Rad Shop.......bit like real or pretend sex, toys may be ok for a while, but nothing beats the REAL thing !
BEFORE PULLING HEADS, get local mechanic to do a RAD atmosphere test with designated TEST EQUIP which detects CO (Carbon monoxide) in the Rad , and also how concentrated which helps isolate if heads are cracked. "WEAK" may indicate just gasket/s. Even if rep heads with D port, get old ones tested, so ur not putting new Heads on maybe a cracked Block !

"the only other thing i could think of if the pressure is holding is either some broken fins in the water pump or rusted out fins  that doesnt allow it to pump water thru the engine fully"
 
That's exactly what I am tippin', or restricted coolant flow through radiator. But as BeeVee mentioned may now be subsequent damage also. With these sort of issues usually there is a sequence of problems not just one.

Wiggy
I am not a mechanic & do not have the mechanical expertise that others on this forum have but I am just a silly old bugger who mucks about with Capris. So, I will add my 2 bobs worth but I think it has already been covered.
I had a similar problem with my 1600 Capri & couldn't work out what the problem was until another club member alerted me to the fact that I had the wrong radiator cap. As you have already said, you have tried both the recovery & non- recovery types. When I went to buy a new cap at Autobarn, the guys usually do not even know there are two types & the new Tridon caps have no markings on them to distinguish which ones they are. The part numbers are Non-Recovery-Tridon CN1390 or CPC 508-13 & for Recovery - Tridon CA1390 or CPC543-13. I am not sure if they are the same for the V6s but having the correct cap solved my problem.
If you want to read more of my story on my blog, this is the page with some pics:
http://fordcaprichatter.blogspot.com.au/search?updated-max=2016-02-22T03:57:00-08:00&max-results=7&start=14&by-date=false
Hope you don't have to do some serious work on the motor.
Cheers
Ian

Just to illustrate how cool these V6 engines run, I have driven countless kms without Fan Blades, no Thermo fan, no Shroud and no Panel between rad Sup Panel and Top rad tank.............................
Thanks to a TOTALLY CLEANED OUT Rad, 74 degree thermostat, very clean Block/water-jacket, 50% AFAB coolant, and a well tuned engine.
Only disadvantage: without a fan you cant risk heavy slow traffic esp on hot days.
Main advantage: more power, less wear/tear, and better fuel economy. 
Am soon to try eliminating Fan Pulley/Bearing with shorter Belt.
Any cons; none
Any pros; same as above 3 lines up