I Have a 3.9 V8 Discovery and on long runs (70 miles) it starts overheating...water boiling up and wanting to escape out of the header tank, i'm sure the head gaskets are fine can anybody help ? i think it might be the Thermostat ?
feel top hose if hot thermostat all right,if not remove and test vehicle ,but also could be poor rad feel rad all over to make sure cooling effectively ,or could even be cracked bore behind liner
As above but normally thermostats fail in defalult mode ie. closed and within 4 or 5 miles you will see the the temp rise above the norm unless it opens, I would replace the header tank cap first unless u have other symptoms
