I have read about a possible issue with the Ford C-Max and the fuel filter becoming easily blocked with emulsion, which forces the car to go into limp home mode. This happened to me and with a fuel error coming up on the diagnostic and we changed the filter and all has been OK. But a later observation has made me question this action and I wondered if you had any views.

The event happened soon after a refuel and every time as I add my Millers diesel additive following each refill. When I do so, I always trigger a "whoosh & gurgle" when I insert the funnel. It has a misfuel prevention type filler cap. Clearly there is a back pressure developing.

Might this have been the cause of my problem, not the filter itself? How might I get the tank to vent correctly when full to avoid the problem?