D4, D6 cooling problem

If your D4,D6 is not cooling properly, it may be due to the outlet at the bottom of the expansion tank not being drilled out sufficiantly. Hole size should be 10.7mm X 50mm deep. If filling the engine with coolant takes longer than 2.5 minutes this may well be the cause and would certainly warrant investigation. If this is found to be the problem it is possible to drill out to the above dimensions but be careful to remove any drill swarf