Image: wjrneo2/YouTube (screengrab)

For many months, Ford Focus RS owners around the globe have been freaking out about head gasket failures. The issue has led many to believe that Ford screwed up its gasket design, but in recent weeks Road And Track posed a different theory: the gasket wasn’t flawed, per se; it was just the wrong part. I looked into the issue too and this is what I found.

We already covered the Focus RS head gasket issue in our in-depth technical explainer in November, but it’s worth reporting this new theory about what may be the root cause of the failures—a theory that looks to have originated on forum FocusRS.org—because it seems more plausible than other guesses I’ve seen floating around message boards.

In his Road & Track article, sentient Bill Of Materials (and occasional Jalopnik contributor) Bozi Tatarevic points out that the couple of failed RS head gaskets he’s seen online look exactly like what might be found between the block and head of a Ford Mustang EcoBoost, which has the same 2.3-liter motor as the RS but with several notable differences.

Tatarevic told me over the phone that he has info from a Ford Engineer and a Ford parts employee indicating that the engineering part number found on at least one failed Focus RS gasket (a number that starts with “EJ7E”) is the same one for the head gasket of the EcoBoost Ford Mustang, and also the Lincoln MKC and Ford Explorer. (The Focus RS’s head gasket engineering part number should actually start with “G1FY,” Tatarevic reckons).

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Why This Theory Could Make Sense

Image: Ford

The Focus RS should have a different head gasket than other 2.3-liter Ford EcoBoost models. We know this for sure, because Ford itself, when launching the RS in 2015, said the hot hatch’s engine received a “more robust head gasket with improved thermal capability” over the Mustang.

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Plus, as FocusRS.org forum members Alex@Stratified, LiquidM4 and Regulated point out, there are a number of differences between the RS’s block and the Mustang’s block that should necessitate two different gasket designs. An important difference deals with how the engines go about keeping the thin metal section between the cylinder bores—called the “bore bridge”—cool. Regulated mentions a patent that apparently shows the Ford Focus RS’s bore bridge cooling strategy; the patent describes why keeping bore bridge temps down is so critical, saying:

In a water-cooled engine, sufficient cooling may need to be provided to the bore bridge between adjacent engine cylinders. The bore bridge on the cylinder block and/or the cylinder head is a stressed area with little packaging space. In small, high output engines, due to packaging, the thermal and mechanical stresses may be increased. Higher bore bridge temperatures typically cause bore bridge materials to weaken and may reduce fatigue strength.

It goes on, saying:

Thermally weakened structure and thermal expansion of this zone may cause bore distortion that can be problematic to overall engine functionality such as, for example, piston scuffing, sealing functionality and durability of the piston-ring pack. Additionally, high temperatures at the bore bridge area also limit the reliability of the gasket in this zone, which in turn may cause combustion gas and coolant leaks, and/or reduced engine power output and overheating.

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(By the way, I emailed Ford for comment on all this, but have not yet gotten a response.)

To understand how the RS’s and the Mustang’s bore-bridge cooling strategies should require different head gaskets, let’s have a look at some photos I included in the Focus RS explainer I wrote in November. One of those images, taken by Alex, an engineer at British Columbia-based tuning company Stratified (and also the original poster of an enormous thread about failing head gaskets on FocusRS.org), illustrates what one Focus RS’s failed head gasket looks like.

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This head gasket has one hole on both sides of the bore bridge between cylinders, and a gap in the elastomer between the holes. It looks quite similar to the Mustang’s head gasket shown below:

I’ll admit that I’m not too familiar with head gasket design, but this gasket does seem to make more sense on Ford Mustang/Lincoln MKC/Ford Explorer EcoBoost engine than on an RS, since the former group of cars have a groove (seen below) in the area between the cylinders to keep the bore bridges cool.

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Image: Ford Performance

One of the head gasket’s main jobs is to strategically block off the engine block’s cooling jackets to guide water into passages in the cylinder head. Looking at the Mustang’s block and gasket, it appears that coolant flows out of the cooling jacket surrounding the cylinders, and into the groove between them, but only from the intake side (notice how the groove doesn’t reach all the way across the bore bridge).

From there, coolant flows until it reaches the end of the groove, at which point it exits the hole in the head gasket, and flows up into a passage in the cylinder head. This is how Ford’s 1.6-liter EcoBoost works as well, as Alex from Stratified shows in his forum post.

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But, as shown in the two gasket images above, unlike the 1.6-liter EcoBoost, the 2.3-liter Mustang’s gasket also has a second hole in the bore bridge area that doesn’t line up with the cylinder head inlet (which, again, is above the end of the block’s cooling groove). Alex and I surmised that the second hole likely allows for coolant to flow on the top side of the gasket, across the cylinder head bore bridge, and out of the hole in the head.

In other words, the Mustang’s groove design, along with its gasket that has two holes with a gap in the elastomer between them, means coolant should be able to flow from the groove between the cylinders into either hole in the gasket, and then into the single passage in the head, keeping to the bore bridge of both the block and head cool.

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While I’m not certain that I completely understand the coolant flow path for the Mustang’s EcoBoost engine and head gasket, the Ford Focus RS’s bore bridge cooling strategy seems fairly straightforward, and it appears to be incompatible with the EcoBoost Mustang’s head gasket.

Its engine block, unlike the Mustang’s, does not include a groove between the cylinders; instead, each bore bridge has one cooling hole on the deck surface. The approximate location of a second hole, based on the previously mentioned patent, is marked in yellow above.

Looking at the patent, it seems that the way the RS keeps its bore bridge cool is via a v-shaped cooling passage below the deck that starts at that second inlet on the vertical face of the cylinders (on the intake side of the engine), passes under the surface through the bore bridge, and exits out of that single hole in the deck.

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The section cut through the bore bridge shown above provides a look at how that v-shaped cooling passage in the RS probably looks. Notice how the gasket, labeled 104, covers the cooling jacket on the exhaust side of the cylinder (134), and creates an aperture for coolant to flow from the cooling jacket on the intake side of the cylinder (130), through that second cooling passage in the block on the vertical face, out of that single hole on the deck, and into the cylinder head.

A head gasket that seems to make sense for this design is the one shown below, which many Focus RS owners have considered the “revised” gasket (but, based on Tatarevic’s theory, it could really be the “correct” gasket). There’s one hole (corresponding to the aperture in the image above), and no gap in the elastomer between cylinders.

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To see how putting a Mustang gasket onto an RS could cause a failure, let’s look at the Mustang’s gasket again:

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If this gasket were put onto a Focus RS, which Tatarevic and a number of forum members think may very well have happened, coolant would exit the single hole in the block through 178 shown in that patent drawing above (corresponding to the yellow arrows in the picture), and then have two options: it could go into the hole in the cylinder head, or it could flow in the elastomer-less gap between the cylinders. But since there’s no hole in the head (or block for that matter) corresponding to that second hole in the gasket, the coolant would just stagnate between the gasket holes.

Looking at Alex’s image of the cylinder head (and also the block image shown before) of a failed Focus RS engine, you can see that that’s exactly what appears to be happening. The first hole in the gasket lines up fine with the cylinder head hole, but the coolant doesn’t just flow into the head, it also floods the area between the cylinders and likely stagnates. This stagnation, Tatarevic and forum member LiquidM4 think, could eventually lead to coolant boiling in that area, and ultimately degradation of sealing performance.

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There Are Still Some Unanswered Questions

I’ve read all sorts of theories about why Focus RS owners have been experiencing coolant loss, steamy plumes from their exhaust and misfires. Some suggested that the head gasket was flawed, others thought perhaps the “open deck” engine design allowed the cylinders to flex and wear away at the gaskets, and still one person thought a cylinder head bolt was causing blocks to crack.

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I don’t know much about head gasket design, but I’ll agree with VW Vortex forum-goer BRealistic when he references Occam’s Razor, the idea that the theory involving the fewest assumptions tends to be the best one. Ford putting the wrong gasket onto the RS definitely seems more plausible than the other more farfetched theories.

That said, I’m left with some questions. If Ford really just accidentally put the wrong gasket onto some Focus RSes, then why are Ford dealers allegedly replacing both cylinder heads and gaskets?

Tatarevic thinks that perhaps the boiling fluid in the bore bridge warped or otherwise damaged the head. Alex from Stratified told me over the phone that it could just be a matter of Ford minimizing risk of having to do the job over again if, for example, the tech doesn’t properly clean the head surface. Both reasons sound plausible.

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But what about Ford’s lack of a real response describing the cause of the issue? Surely if they just put the wrong gaskets on, they’d have issued a recall or at least a technical service bulletin by now, right? Not doing so seems like a silly PR move.

Another question I’m left with: why aren’t the affected cars from a certain “batch”? It seems like various Focus RS builds spanning 2016 and 2017 are affected. You’d think that if the wrong head gaskets were put onto Focus RS engines, you’d be able to identify a certain range of affected VINs? Tatarevic told me “That, I have no way to explain. And it doesn’t make any sense.”

Still, while there remains a lot of mystery behind this Focus RS head gasket issue, at least now there’s a plausible theory for the cause.

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When we’ll find out for sure if this whole issue was just a simple case of mixed up gaskets, I have no idea.