The heater of my 5yr old Diesel 2.2 Nissan X-Trail T-Spec has never been much good and only starts to give out heat when the engine has warmed up after 10-15mins of driving. This is a real nuisance in severe winter weather because I can't use it to defrost my windscreen. My partner's petrol MINI One has an excellent heater and her car warms up within a few minutes and certainly long before the engine reaches its optimum operating temperature. Should my heater work better than it does?