Ford Focus 2005 1.6 Petrol - Temp Gauge/Cooling

I have seen previous threads on this subject, can anyone point me in the right direction to a running thread. I have bought a lemon, I am crap at buying cars. I bought a focus 1.6 petrol estate as a cheap run around, however a problem I have is when you go above 45MPH, the temp needle starts to flicker, jumps into read, drop speed or hit traffic lights, back down to half. if you are on a dual carriageway or worse motorway, it shoots into red, then the ECU light illuminates, then the warning light and Limp mode kicks in. Pull over, turn off wait 5 mins and start the process again. I have had the car on diagnostics, and no fault codes or signs the engine is overheating however cannot pin it down. I have had the rad changed out and in place of the air con rad a basic non AC rad. Thermostat changed, Temp sensor to cylinder head changed. New coolant tank lid.

The car does not lose any coolant???  The heater never loses heat. The fans kick in on the rad. 

If I can't resolve this by the end of the week I am flogging it as spares. Done. 

What I do notice is levels to the coolant tank. before starting off my routine is to check to see if there is any coolant. It has been at the same level for months, mid way between full and empty. However when I check once the temp gauge goes on it's dance, it is at the max line sometimes higher. A lot of gurgling is taking place with coolant dribbling out the top RH small bore pipe. 

The rad hoses to the RH side are hot, the LH side are cool. 

I am now at a loss where to look next. Do I strip the coolant pipes down?

Replace the water Pump?

Replace the ECU and Instrument Panel?

Install Ford TSB  005/2001 to splice in new pipes to the existing, replace coolant tank, new thermostat with lower degree spec?

Thanks for taking the time to look

Forgot to mention. When the engine running, if you remove the oil filler cap, there is a blowing similar to the firing of the cylinders, very weird. I have heard of the cat failing and causing blockages???

Edited February 23, 201610 yr by 63 Oahu
Another quirky oddidty