My VW Golf GTX_Twin turbo overheated last night while driving back home. on 1999 Volkswagen Golf

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The problem happened last night when I noticed the temperature going beyond half. I managed to reach home but when I opened the bonnet I noticed the exapansion tank was full of coolant, not circulating and the fun was not running. I waited for the system to cool off and when I open it most of the coolant had leaked off at the pipe which connects to the engine (I assume that is were the thermostat is located). I put in fresh water and some coolant and it appeared to have behaved. This morning the same thing happened so I had to park it. What could be the problem and what is the solution? It is a 1.8cc 4 cylinder.
(2) Answers
Have a combustion leak test performed at most any repair shop to check for head/gasket problem forcing coolant out of rad. Fans will not work properly if coolant forced into recovery tank leaving radiator very low of coolant. Fan switch needs liquid to activate. Driving in city stop and go or will it overheat at speed also?
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