Engine reliability is very important as it is the most expensive part of your car to replace. As such, understanding what type of engine you have can help you understand how sensitive it is to certain conditions. An important factor in engine durability is the style of the head, where open cover, semi-closed and closed cover systems differ greatly in their construction.
What is an engine “cover”?
When describing an engine, the “cover” is the area on top of the engine block and cylinders. Depending on the type of engine, it may not be at the top when you look at it with the hood open. For example, Boxer engines, like those found in Subaru cars, are aligned so that their covers are on the sides of the engine.
Simply put, the cover is the area between the cylinders and the rest of the car, and is where the head gasket is located.
Open deck engines are the weakest
Cars with open deck engines are notorious for their reliability issues. Some vehicles include late 90s Subarus like the Outback and Impreza, along with some early 00s models like the Baja and STi.
These engines are prone to exploding because there is no material between the engine block and the cylinders. This open space is how they get the name “open deck”, and it was a common failure point for an entire decade of cars.
In essence, the lack of support allowed the cylinders to flex excessively, especially under heavy acceleration or when turbocharging. And while catastrophic failure isn’t the most common, these engines can blow dramatically under the right (wrong) conditions.
However, most of these engine problems are related to the surrounding components, namely the head gasket. Because the cylinder walls flex a lot, they wear at the head gasket over time. This eventually allows the coolant to enter the cylinders, where it affects the engine oil and can cause internal damage.
In addition, the sudden loss of coolant can also cause overheating, which has its own set of problems that are not easy to fix.
In addition to Subaru, many Honda engines are open deck, along with certain Nissan engines from the early 2000s.
Semi-closed roof construction
Semi-enclosed deck engines are less prone to failure because they place some support between the cylinder walls and the engine block. This construction means less overall cylinder deformation and therefore less wear on surrounding engine parts.
Most modern Subaru engines are semi-enclosed rather than open, and it is one of the most common engine types available today.
Closed deck engines are the most reliable
As you can imagine, closed deck engines are the most reliable and strong of the bunch. They are almost solid between the cylinder walls and the block, leaving enough space for the coolant passages. This means virtually no cylinder deformation and long lasting engines. And if you need any more proof of this, consider that the Toyota Camry and Corolla use closed-deck engines and are easily capable of exceeding 200,000 miles.
Not sure what type of engine you have? Look at the head gasket
If you’re trying to figure out what type of engine is in your car, find compatible head gaskets for sale. If the head gasket is mostly solid with only a few small holes around the edges, it is most likely a closed deck motor. Whereas if it is mostly open, with only thin strips around the cylinders and engine block, you have an open deck engine. Finally, a semi-closed deck head gasket will look a lot like an open deck, but with small corresponding bridges on each cylinder.
