A problem relating to the car's head gasket can cause early versions of the 2.3-litre Ecoboost engine to burn coolant fluid, creating white smoke during cold running.
"Owners of 2016-17 Focus RS vehicles are being offered a free inspection and repair, regardless of warranty or mileage status, for concerns of white exhaust smoke and/or coolant consumption stemming from an issue with cylinder head gaskets," the brand said in an official UK statement.
"Ford dealers will test the cooling system, replace the cylinder head gasket and may replace the cylinder head, as required, at no cost to the customer."
Ford UK has set no deadline for owners to bring their cars in by.
Prior to the statement, Ford had already replaced several affected engines with all-new units built to the latest specification under warranty. No official line as to the root cause of the problem has been released, but a large number of posts on internet forums from Mk3 Focus RS owners have suggested that the head gasket is failing to seal the engine block to the head effectively.
Rather than being a design issue of the head gasket itself, the problem has been linked to block distortion. It is believed that the physical shape of the engine changes through multiple heat cycles, eventually preventing the gasket from sealing the two parts correctly.
This, owners have suggested, is allowing coolant to leak into the cylinders when the engine is cold, causing issues such as a smoking exhaust and misfire before the engine is up to its optimum temperature.
A Focus RS owner, YouTube user MarkCup70, claims in a video that he has come across a dealership report stating that another car with the aforementioned symptoms was “losing coolant” due to the cylinder block being “out of tolerance”. The report concluded that the car now had a “distorted cylinder head”.
The problem is not thought to affect Mustangs with the same engine due to the use of a different alloy for its block and head. The Focus RS’s engine is made from an upgraded alloy with a cast-iron lining and gets its own head gasket design – requirements for the car’s higher 345bhp output.