I seem to have a slight coolant leak on my 156 1.9 JTD- I have had to top up from just below the minimum line to the max twice in about 1500-2000 miles. Is this normal (I can't imagine it is), I can see no sign of a leak. There is no obvious evidence of a head gasket problem i.e sludge in oil or white smoke. The car does not run hot- if anything it runs cool, 70 when moving, 90 in traffic. Any ideas?