First question, why did you change Rad,Pump,and Thermostat ? second question, are you getting water in the oil ? Sounds to me as if it has over heated and warped the head(or alike) and pressurizing the water system ! Radiotwo Hi items changed because pump impeller was loose on spindle and radiator was blocked. I have had a sniff test done on coolant, all OK. No suggestion of gasket leak.No sign of water in oil, no brown residue etc