Ok, so replaced the expansion tank cap with a brand new one. No air is escaping via the braded hose anymore when I squeeze the radiator hose. But the main radiator hose stays soft even on hot, is this normal? In my old 1987 D the hose was unde pressure when it got hot. Does this mean I need a new thermostat or something? Again the car does not overheat and there is no coolant loss...

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1987 300D
2005 E320 CDI