I've got a W124 Brabus 3.6 saloon/sedan based on a 300E M103 engine (SOHC). When I go on long journeys, for instance today I travelled 100 miles to Leicester (cruising around 70-100mph most of the way), the car loses around
2 litres of water. It only starts overheating when in traffic. I have checked all water connections except for the ones where the heat exchanger is but as this is a recent problem I don't see how that could be a factor. I filled the car with water and just made a 15 miles journey and there was no water loss. The thing that makes me think it is the head gasket is that I can petrol in the expansion tank. However there is no oil-water mixing as I would expect to see with a blown head gasket. When the car is water deficient the oil pressure gauge is unstable floating around 1 bar erratically. Any ideas?Thanks