I have a '95 968 which has developed a thirt for using coolant. I have checked the header tank for signs of oil and the oil for signs of water but none is present in either. I have changed the thermostat and flushed the system. I have looked at the bores and none appear to be clean. Last week I used approx 3/4 litre of water in 10 miles. Any ideas.

 

Is it overheating or at least getting very hot? Are you getting any puddles of coolant under the car / steam from anywhere? The coolant must be going somewhere?

 

Any white smoke coming out the tail pipe, especially on start up? Any drips on the driveway? The coolant tanks have a tendancy to get pinhole leaks in them, which can lose a lot of coolant. What i would do if the car is not over heating, is start it, and let it run in the driveway for about 20 minutes. That will get it warm enough that the thermostat has to open and move coolant. Any leaks should be visible with the car running and hot. If it absolutely isn't leaking, and isn't in the oil, then you probably have a head gasket going out.