Over the last week Iâm getting an unexplained coolant loss,which is being chucked out of the expansion tank. The cars has had the following work done on it, new water pump, thermostat, temperature sensor, new expansion tank and cap, new G12 coolant. I only start to see the loss when the car is sitting ataround 70-80MPH, any higher and it will chuck the stuff out quickly. Since Sunday I would have lost around 5-6 liters (could be more) Also notice that when you release the pressure, the expansion tank can go from being almost empty to around half full. What Iâm NOT getting is the following, no oil in the wateror water in the oil, no mayo oil cap. No trouble starting the car, no faultcodes on the engine, no smoke coming out the exhaust. Questions! Could this the exhaust gasses going into the coolant?What sort of pressure should be in the coolant system? As the pipes are justabout solid when the car has been run.