The Cause of the Ford Focus RS Head Gasket Issues Has Been Discovered
It appears to have been a case of mistaken identity between head gaskets for the Focus RS and the Mustang EcoBoost.
Ever since the Ford Focus RS hit the streets there have been tales of catastrophic engine failures, such as this one last March. Ford has not made any public comment on these failures nor the cause of them, other than to direct owners to their dealers to have the problem repaired under warranty. It seems that Ford has been quite good about covering these repairs. But what caused the problem in the first place?
Bozi Tatarevic is known for his particularly in-depth research on various automotive topics. He turned his sleuthing skills to the Focus RS head gasket problem, and in a Road & Track article he seems to have made a stunning discovery: The failed head gaskets appear to be designed for the Mustang EcoBoost, not the Focus RS.
Both the Focus RS and the Mustang EcoBoost use 2.3-liter four-cylinder turbocharged engines, leading to the assumption both cars use the same engine. (I have myself been guilty of this assumption in the past.) This is not correct, however. As Tatarevic explains in detail, despite the similar designs the coolant passages are different in either engine, which requires head gaskets unique to each engine to allow proper cooling. The Mustang head gasket blocks certain passages in the Focus RS engine, causing coolant to get stuck, boil, and eventually ruin the head gasket.
It is unknown precisely why the wrong head gaskets were used in the failed engines. It's possible that a supplier labeled them ambiguously or incorrectly. Or perhaps Ford got them confused since both engines are so similar. Wherever the fault lies, it would certainly explain why this issue has occurred. Either way, it does appear to be Ford's responsibility rather than the owners of the affected cars. Ford is doing the right thing and covering engine repairs or replacements under warranty without question.
It should also be noted that the internet seems to have blown the commonality of this problem out of proportion. Yes, this is a serious problem that should never have occurred. Yet it only seems to have happened to 3 percent of all Focus RS models made. A spreadsheet on the FocusRS.org forums currently lists 48 cars known to be affected. Compared to 3,500 cars sold as of last March according to Motor1, it's a very small proportion of cars built that actually suffer from this problem. Remember the numerous head gasket problems reported by owners of Subarus in the mid-2000s that Subaru did nothing about, in comparison? The Focus RS has gained a bad reputation for a problem affecting only a small number of actual cars.
With any luck, this problem should be fixed for the final 1,500 models to be produced for the 2018 model year.