Hi Jonathan, Is the leak around the outer edges of the water-dome or from around the spark-plug ferrules ? In any event you will have to remove the dome to renew the gaskets and seals. Normally the white efflorescence is glycol from antifreeze, but I suppose it could be an aluminium salt if you have a lot of corrosion occurring. Never put hard water in your engine. Use rainwater, distilled water, or deionised water. I have a dehumidifier in my workshop, so always have a good supply of the latter. Also always use a suitable, ethanol-free antifreeze at about a 30% strength in the system. Remember that with at least three different metals in wet contact in your cooling system, cast iron, aluminium, brass, and also nickel if you have a ‘modern’ replacement radiator, you will get electrolytic corrosion happening unless the coolant mixture is correct, and aluminium is the first metal to suffer, hence the ‘sacrificial anodes’ fastened to the hulls of steel ships and boats.
Brian
