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Join Date: Feb 2009
Location: South Africa
County: Northern Cape
Re: Where`s my coolant going ??
It sounds like a head gasket leaking. The coolant is sucked into the combustion chamber and blown out into the exhaust, thus the loss of coolant. Upon combustion, exhaust gases are forced into the cooling system, pressurising it, thus the hissing sound. To confirm this, remove the cap and smell the gases blowing off. The antifreeze in the coolant has a sweet fresh smell. If you can smell exhaust fumes, then you have confirmed that the gasket is leaking.
You should take remediate action as soon as possible to avoid progressive damage to your engine. If left unchecked, the water entering the combustion chamber will erode away a growing slot into your cylinder head or crankcase. The engine will start missing at idling speed, due to water vapour on the spark plug. The water will loosen carbon deposits from the cylinder head, some of which ends up between the rings and cause scratches and grooves on your sleeve walls.
I had a similar experience a year ago with a car I bought for my son (a student). I got away with minimal damage and even repaired a slot in the head between the water-channel and the combustion chamber with liquid metal, without having the head skimmed. It is important to have all mating surfaces absolutely clean before assembly, using a new paint scraper to remove protruding old gasket matter. The car is fine now, having done about 15 000 km without having to add any coolant.