Before flushing, remove thermostat for full flow. Then REVERSE FLUSH the whole system inc Rad, or separately, but reverse F~ both the RAD and the Engine.  Before re-fitting Thermostat, bench test it whether it's the old one or a new one, and ensure it opens and closes correctly as per instructions on a reputable "Engine Service" website. 
 
Even tho I dont think this is your problem, theres no harm in ensuring a clean Cooling System.
 
If you know the history of your heads, and you know theyve never been over-heated, then you're very unlikely to have hairline cracks in oem Cast Iron Essex Heads.

A clean out at my local rad guy is $150.  Recores for the V6 are $450+ as there is only one supplier now of the required core-there is some part that makes it unique.

in rod we trust

gtv6capri
wow thats expensive flush.  Just take the radiator out and drop it into a Natrad or local repair shop for a dunk in the tank and a pressure flush, also make sure you have a thermostat fitted

I rag natrad and that quoted me 800 + for a recore so I would imagine that a dunk and clean would cast about half that...   a new 2-3 core would cost 250 in alloy..  it is expensive rad cleaner but seem to be th best one on the market that works ,  it flushes the block and rad at the same time , no real use in doing a rad change unless I try remove as much scale out of the block as well so I don't end up with another block rad ..  other than that I was going to pull the heads off to convert to unleaded valve seats this yr and new valve stem seals as well , so ill just have a good think on when or what stage to do it..
 
I took the capri out yesterday just local drive and kept a eye on the temp didn't get to half way as it was bit cooler yesterday but had thermos fan on , it didn't stall at all .. but I know if it reached half way it would of stalled and ran like crap , missing and stalling . its weird alright as I remember when I put new head gaskets on one looked dodgy I put them on and 4 months later head gasket blew and in the spot I thought was dodgy payen gasket.  it heated up way over half lucky I was only 2 min from home but the car didn't carry on like it is now at half way .. it stalled few times when it was blown in the 2 min to get home ..  the only thing I can think is just maybe the temp switch being as they are is showing less than what it really is and at half way its actually running very hot , but I have no way coming out of over flow tube .. so I think I try the flush and get new alloy rad as I can find any that resemble oem one 

HEY ROD !
 
The only thing you havent changed is your IGNITION SWITCH &/or COIL POSITIVE IGNITION WIRE/ballast resistor ........ !
 
ASSUMING POINTS ARE STILL IN, DO THE FOLLOWING which takes 5 minutes, and bypasses all above !  .........
 (if electronic, youll need to check with maker on safe method to "hotwire" the ignition)
 
Get a regular piece of auto insulated wire with Aligator Clips at each end.
Place one Clip on POSITIVE or IGN side of Coil ...........(NEVER on neg Points side),
connect other Clip to POSITIVE BATTERY TERMINAL. 
 
After youre sure "jumper wire" is secure, start the engine and go for a roadtest. If it continues to behave, ALWAYS disconnect the jumper wire when you're no longer running the engine and/or parked the car..... Re-connect and disconnect each time you use the car, until youre convinced theres no more poblems. 
If this proves the problem, start with looking for a "broken wire" or loose connection in the Coil to Ign Sw Wire before replacing the more complicated job of Ignition Switch, assuming you havent got loose connections at the actual switch itself.
 
nb...........  when you go to turn off engine at key, it will likely keep running until you disconnect "aligator clip" at Coil FIRST 

cheers boys ..  I started on the rad flush as mention not cheap at 150 for part a and b …  but it does up to 30 + litres depending what your cars are . so it will go into the vk as well , put part a in today started it let it get warmed up then shut if off , will do the same again tomorrow until liquid goes clear from green looking crap..  should of taken pics before and after but too late now...
 
hey beevee  iwas thinking of doing that as well , bypassing the resistor but I always thought when resitor fails it would fail at almost point noy just when car gets  halfway..... I have this feeling its a manifold gasket , or the start of headgasket leaking  as there is nothing else I can think as while it would always do it at half way temp, wasn't evetr getting to half way when I first had it running  so something is getting it hot and making it stall and as mentioned when running just above the blue it runs perfect and doesn't miss a beat ..

Can 100% Guarantee you it wont be IM Gasket .............  try my suggestion as above as it only takes 5 seconds
 
This way, (starting at simple things first), you wont feel so bad after many hours of un-necessary work that gives you zero results
 
Hey Rod, it's not only the resistor you're bypassing; it's bypassing ALL your ignition wiring AND Ignition Switch which have potential for MANY partial breaks in the wires at ANY point, and poor/loose/worn-out IGn Sw Contacts !!!!!!!!!!!

yeah I will try the bypass wire .. I still think there is a slight manifold leak tho  as I can see the revs climb a bit when it gets upto operating temps..  just might be the risitor wire ...
 
is there any way of testing the resistor on cold and hot 
 
 
I think it also may be as mentioned loose or broken wire ..  ill go thru and re check the connections ..  might be something there as it stalled coming to a roundabout  tried to clutch it but wouldn't kick until I turned ignition off and then on again then it started.. so could just be a wire getting hot or bad connection .. just wierd as it will go for quite a while then decide to play up when it gets to half way or i park the car then go again 30 or so min later it will do it for a bit then run fine ..
 

Have you tried the "hotwire" 5 minute test yet (Pos jumper wire from BATT POS to COIL POS) 
 
Never Bat Pos to Neg points side or you'll have melt-down damage immediately! 

What ignition coil are you running 9v or 12v. As Bevee states it might have something to do with Ballast wire. I prefer nowadays to get rid of it and run a 12v as batteries are much better 50 years on. If the ballast wire is old it heats up more and causes a fire issue or maybe in your case just more resistance and failure. When it cools you get it driving again. You maybe need to get it on the open road for a good clean out on the open road for a solid hour of just driving without stopping which could work wonders or show the real cause.

Im in suspenders waiting for this "hotwire" test ............. a 1 minute job that tells a lot
 
Have you done it yet ?

happy new yr fellas 
 
no haven't done the hotwire yet as im sure running the electronic system I have to do it a different way I think my coil could be 9v as its a 1.5ohm's 
 
but had a bit of time so off came the top end and decided to change head gaskets.  it was lucky I did as I notice one was probably on its way out.
but that didn't change the issue thought it was only happening when hot but it does it when it feels like 
 
im going to remove the carby and check the float doesn't have a pin hole in it as a friend of mine had similar issue 
 
i have to get another radiator first as mine is pretty **** and the flush didn't really clean it out that much.
 
as i really need to get that right before doing the hot wire test .. 
 
has anybody brought a alloy one for there capri that might be able to direct me to where I can buy one.. 
i have seen these on ebay but not sure if they will be ok .
re doing mine is going to cost 800 odd so I think a alloy one at 260 might be a better option for now
 

https://www.ebay.com.au/itm/ALUMINUM-RADIATOR-FORD-CAPRI-RS-ESCORT-SUPERSPEED-MK1-ESSEX-V6-2-6-3L/262012747111?fits=Model%3ACapri%7CMake%3AFord&hash=item3d012d3d67:g:uLYAAOSwd0BV1WuU
 
https://www.ebay.com.au/itm/3Row-Radiator-Ford-Capri-MK1-MK2-MK3-Kent-1-3L-1-6L-2-0-Essex-Escort-RS1600/193002907384?fits=Model%3ACapri%7CMake%3AFord&hash=item2cefdea6f8:g:UzAAAOSwVZtdMpku
 
just have to see what size the hoses are as some of these are 38mm and some 35
would the above ones be ok to use
im still thinking its a fuel issue rather than electrical