Overheating, what makes a Subaru a Subaru! But hopefully it's just the radiator cap

Only the open-deck EJ25D/251/253 experience this type of failure; where the cylinders & deck surface are not connected. From what I understand, there were multiple issues (bad grounds exacerbate the issue) that sometimes combined, but the root of the issue was the single-layer coated gasket that failed as the cylinder & deck expanded at different rates, and the cylinders basically rub the coating off from this action until they leak. Supposedly, the closed-deck EJ255/257 nor aftermarket conversions to closed decks suffer the same fate, but most of them also got an MLS gasket instead of the single-layer that was originally used.

Maybe somebody smart like Trav can confirm, since like I said none of mine have actually failed.
Spot on! The open deck engine were a real POS, the closed decks were great and had 200K and more in them easy if they were maintained and like all Suby engines the grounds were taken care of.
Even the open deck engines were okay if instead of just changing the HG the case was split and the bores honed with a deck plate (hot honing is even better if you can find someone to do it), the cases decked and the heads planed and using a MLS HG. They will last a long time.
Again with these engines it is grounds, grounds and grounds, these fail and coolant electrolysis really buggers the engine.

An older article but still relevant today.

 
Spot on! The open deck engine were a real POS, the closed decks were great and had 200K and more in them easy if they were maintained and like all Suby engines the grounds were taken care of.

Again with these engines it is grounds, grounds and grounds, these fail and coolant electrolysis really buggers the engine.
Exactly. Like we’ve both said the factory grounds are not sufficient even brand new; I forget the company I went with but their ground kits go from both strut towers, across the top to the TB and alternator case, and on the bottom side from the frame to each head.

“They” say it will result in a smoother idle; that’s so subjective so I won’t comment on that. But the engine definitely cranks better and like I said I’ve never lost a head gasket on the several EJ25s I’ve owned.

And yes, @Slow Car Sport Mode, the EZs never had issues because they are all closed decks. In reality, looking at the closed decks and chain driven cams, the flat-6s were really the pinnacle of Subaru’s engine design.
 
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