Hi Gill .
Sorry to hear of your car problem and i will help you sort out this issue .
If you are sure that there is a leak then you need to check where it is coming from ,due to the leak this is why you are most likely starting to overheat.
First you need to find a good local garage that has good references from the locals friends etc.
What has to be done if the leak can not be located is pressure test the cooling system ,this will help you locate the leak ,
Most common is a waterpump so check here first when the system is under pressure.
After having the system checked by one repair shop you could also have a second opinion at another shop .
Try AutoZone , PepBoys for free diagnostics of the cooling system.
Cooling system leak check at home , make sure the system is full of coolant ,go for a test drive and when hot open the hood and see if there is any leaks ,when the engine is hot the system will be under pressure , so be very careful as you may have a bad hose that may burst, rad cap faulty that may also burst . if you see any leaks wait until the engine cools off then refill with coolant and take it to the repair shop and explain where you seen the leak.
Personally if you are very limited on engine repairs i would leave the cooling system to the pros, so you don't get burnt by scolding hot coolant/water that could blow up in your face .
Still need additional information then please get back to me with the reply button, and not the poor or bad service, this way i can get back to you or suggest another expert if needed.
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Kind regards Greg.