hi, iv got a 2000 on a x td5 with 236k miles and in having problems with cooling as when driving the disco comes up to normal running temp and then some times drops to just above cold but when still with engine running after about 5 mins its drops to just above cold, then if you drive it it all of a sudden comes up to normal running temp.... help any ideas iv replaced top hose and hose below turbo, but it bled up all right and i was getting hot air out vents,