the 10 w40 is to thick for the tappets it will be like treacle and will cause sticky valve cindrome and not open the valves properly or worse cases drop a valve into the pistions or knacker the oil pump up

you should never engine flush a ford engine in fact any engine as it takes the dirty/carbon build up and moves it around and could block a oil gallery or knacker up the oil pump !!!
thats why you dont do it, cost lots of money to fix all because of £3.99 bottle of crap was used so big no no no !!