What could be causing the coolant problems in my Renault Clio 1.2?

I'm having some issues with my petrol Renault Clio Rush 1.2 8V. I had the water coolant tank and stop light show on my dashboard because the engine was overheating. I found there was no coolant in the tank, but last time I checked there was some. The cap was secure, no external leaks, so I refilled the coolant and it seems to be okay. A mechanic has done all the necessary tests but is unable to source the issue. I was wondering if you have any ideas?
If the mechanic has checked for head gasket failure and found no fault, then we would suggest (if not already done) a pressure test on the cooling system, as this should establish any leaks from there. Another thing to check is the expansion tank itself plus the cap.
Answered by Alan Ross on

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