I've always had an issue of having to top up my expansion tank as water level drops to minimum, sometimes below, and the light comes on when I start the car. I have tried many things, including releasing pressure after a drive and checking for leaks, to no avail!

 

Within the last year I have had the Timing Belt and Water Pump replaced and it still continues to lose coolant.

 

Does anyone have any ideas as to why this still occurs? Would purchasing a new expansion bottle and cap help?

 

 

Thanks

I had similar and it was resolved by simply replacing the cap (see eBay). My old one was obviously not sealing properly allowing evaporation.

It may be possible that there is a really small leakage from refrigerator or any collar which may not be visible. ..

You may have to try a specialist appropriate engineer though.