UK Car Repair: Overheating Opel Astra 1995 vauxhall model, opel astra 1995, fuel air mixture

Question
I bought a 1995 opel astra last year and since then I have had never ending problems with overheating. I have had the raditor and bottle cleaned. The mechanic put a ford cap on my water bottle (astra cap didn't provide enough pressure and water leaking through cap) and have had a golf switch put in. Even though the golf switch works and my fan comes on I still lose water. Everyday I have to fill up almost 3L of water. The guy I bought the car from removed the thermostat and made it free flow and did not put in a restrictor which the mechanic said cold be causing the problem. I did a pressure and blockage test and all is fine now. It was an 1800 vauxhall and the engine was upgraded to a 2l vauxhall. Could you please help me I'm at my wits end. Sometimes the fan does not kick in and I have to pull over to fill up water as water comes out the bottle when fan doesn't come on and heat guage almost on hot. Sometimes after a 2 minute drive the engine heats up and the fan doesnt come on and I break down again. I am a lady and want to sell this car as no mechanic or auto electrican can get it right. I have spent alot of money with no results. PLEASE HELP I'm running out of options.

Answer
So sorry for late reply, I replied 3 times by mobile phone but it hasnt worked!


Its either:

The radiator is too small for the engine. pretty sure the 1.6/8 has a simgle core radiator, and the 2.0 has a triple core

(or similar sort of grading).


OR

The ignition timing and/or fuel/air mixture is incorrect

OR

There is a blockage somewhere (in the engine block or cylinder head), or a pipe has collapsed internally.

OR

The waterpump is giving out.. as you said its somewhat intermittent, EG overheating in 3 minutes or overheating after 10-15 then it's failrly likely to be a worn out waterpump.