Subaru Engines 101: What You Need to Know About Interference Engines

Are you a Subaru owner or a potential buyer wondering what an interference engine is? Look no further, because we have all the information you need to know about Subaru interference engines.

What is an interference engine?

Before we dive into the specifics of Subaru engines, let’s first define what an interference engine is. An interference engine is an engine design where the pistons and valves occupy the same space in the engine cylinder, but at different times. In other words, the valves and pistons are not in sync, meaning they can potentially collide and cause serious engine damage.

Interference vs. non-interference engines

Now that we know what an interference engine is, let’s compare it to a non-interference engine. In a non-interference engine, the piston and valves never occupy the same space in the engine cylinder at the same time. This means that even if the timing belt or chain breaks, the valves and pistons will not collide, and the engine will not be damaged.

Why does Subaru use interference engines?

Subaru uses interference engines in their vehicles to maximize performance and fuel efficiency. By having the valves open longer and creating a greater intake of air and fuel, there is more power available to the vehicle. Interference engines also tend to have a higher compression ratio, which results in better fuel economy.

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How does a Subaru interference engine work?

A Subaru interference engine is a four-stroke engine that operates on a horizontal plane. The engine has an overhead camshaft configuration with four valves per cylinder. The camshaft is driven by either a timing belt or chain, which keeps it synchronised with the crankshaft.

In a Subaru interference engine, the pistons travel towards the cylinder head when they fire, while the valves open and close in a specified pattern via the camshaft. The timing belt or chain ensures that the pistons and valves do not collide.

Benefits and drawbacks of interference engines

As we mentioned earlier, interference engines are designed for maximum performance and fuel efficiency. However, they do come with a couple of drawbacks. For example, if the timing belt or chain fails, the pistons and valves will come into contact with each other and may cause significant engine damage.

It’s also important to note that interference engines tend to be more expensive to maintain due to the complexity of their design. Regular maintenance, such as timing belt or chain replacement, is crucial for preventing costly damage.

Common issues with Subaru interference engines

Some common issues with Subaru interference engines include timing belt or chain failure, valve interference, and engine overheating. These issues can be do to a lack of maintenance or other factors, such as engine age or driving habits.

Maintenance tips to prevent issues with interference engines

To prevent issues with your Subaru interference engine, it’s crucial to follow the manufacturer’s recommended maintenance schedule. This includes regular oil changes, air filter replacements, and timing belt or chain replacements at specified intervals.

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Additionally, monitoring the condition of your engine and addressing issues promptly can significantly reduce the risk of engine damage. For example, if you hear knocking or ticking noises coming from under the hood, visit a trusted mechanic and have the issue diagnosed.


In conclusion, Subaru interference engines are designed for high performance and fuel efficiency. However, they do require regular maintenance and care to prevent engine damage and costly repairs. By understanding the basics of interference engines and following a preventative maintenance schedule, you can keep your Subaru running smoothly for years to come.

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Davis Bellew

As a Subaru owner and enthusiast, Davis has a deep understanding of the needs and concerns of Subaru drivers. He specializes in writing informative and engaging content about Subaru maintenance and repair, and his articles are always well-researched and easy to understand. When he's not writing, he enjoys hiking and photography.

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