Are Subaru engine blocks aluminum?

Subaru generally builds its modern boxer engines with aluminum engine blocks, but the critical wear surfaces inside the bores are typically cast iron sleeves or liners. This combination aims to save weight while preserving durability.

Block materials and bore design

Subaru's contemporary engine families unify a lightweight aluminum block with durable cylinder surfaces provided by iron sleeves. The result is a block that saves weight for better efficiency and performance while protecting the bores against wear and heat. Different engine families have variations in bore topology, but the general approach remains aluminum block with steel or cast iron sleeves inside the bores.

Before we dive into specifics, here are the core points you should know about Subaru's engine block construction:

• The engine block is typically made from aluminum alloy to reduce weight and improve heat management.


• Cylinder bores are lined with cast iron (or steel) sleeves/liners to resist wear from steel piston rings.


• Manufacturing and design choices can vary by engine family and model year, so always verify the exact spec for a given vehicle or engine code (e.g., EJ vs FA/FB models).

In practice, this design means Subaru engines balance light-weight construction with a durable wear surface inside the cylinders. The use of sleeves is a common compromise used across many manufacturers to extend engine life without sacrificing performance.

Model and engine family overview

Subaru's engine lineup has evolved from the older EJ family to the more recent FA and FB families. Across these generations, the basic strategy has remained consistent: aluminum block to save weight, with worn-in cylinder surfaces protected by iron sleeves. The Subaru boxer layout itself remains unchanged, featuring horizontally opposed pistons that contribute to a low center of gravity and balanced operation.

EJ family (older engines)

Historically, the EJ engines were built with aluminum blocks that incorporated cylinder liners made of cast iron. This combination helped longevity and wear resistance while keeping weight down compared to an all-iron block.

FA/FB family (modern engines)

In more recent engines, including the FA and FB series used in models like the Forester, Outback, WRX, and others of the 2010s onward, the blocks are aluminum with bore liners designed to withstand wear. These engines emphasize improved efficiency and smoother operation while maintaining durability through liner technology.

Note that exact bore liner materials and deck design can vary by model year and market, so it's wise to check the specific engine code for precise construction details.

Maintenance and implications for owners

Understanding block material matters for maintenance and potential repairs. Sleeve wear can influence decisions around engine rebuilding or bore repair. Aluminum blocks are more prone to certain forms of corrosion if coolant or oil conditions are not maintained, but the presence of robust cylinder liners helps prevent bore wear. Routine maintenance, including using the correct coolant specifications and adhering to service intervals, remains essential for longevity.

For buyers, asking for the engine code and confirming whether a given Subaru uses an aluminum block with iron sleeves can help set expectations for maintenance and potential repair costs.

Summary

Subaru generally uses aluminum engine blocks across its modern boxer engines, including EJ, FA, and FB families. The cylinder bores themselves are typically protected by cast iron or steel sleeves inside the aluminum block, enabling a lighter overall design without sacrificing durability. While there are variations by model year and engine family, the aluminum-with-sleeve approach is the common thread that defines Subaru's engine construction in the current era.

Are subarus steel or aluminum?

Highly Rigid Body
For an ideal balance of both of these qualities, Subaru has created a highly rigid and lightweight body by comprehensively using aluminum materials and high tensile steel plates throughout the vehicle.

Are engine blocks aluminum?

Yes, many modern engine blocks are made of aluminum, though cast iron is still used. Aluminum offers benefits like reduced weight for better fuel economy and heat dissipation, but cast iron blocks are typically stronger and cheaper. The choice of material depends on the engine's application, with aluminum becoming the standard for most new passenger cars.
 
Aluminum engine blocks

• Advantages:
  • Lightweight: Reduces overall vehicle weight, leading to better fuel economy and performance. 
  • Better heat transfer: Dissipates heat more efficiently, which can help with cooling. 
  • Modern technology: Modern casting techniques allow for more intricate designs and are common in most new gasoline engines. 
• Disadvantages:
  • Lower strength: Generally not as strong as cast iron, so designs often compensate with thicker walls, reinforcement, or the use of special alloys. 
  • More susceptible to warping: Can warp more easily in extreme overheating situations. 

Cast iron engine blocks

• Advantages:
  • Stronger: More durable and can withstand higher internal pressures. 
  • Cheaper: Typically less expensive to manufacture. 
  • Less thermal expansion: Less prone to warping than aluminum. 
• Disadvantages:
  • Heavier: Significantly heavier than aluminum, which impacts fuel economy and performance. 

Which is better?
The "better" material depends on the vehicle's requirements. Aluminum is favored for its efficiency, making it the material of choice for many modern cars and performance engines. Cast iron is often still used in heavy-duty applications where its superior strength and durability are more important than weight savings, notes Auto Truck Service Inc..

What is the most common problem with Subaru engines?

One of the most notorious issues plaguing Subaru vehicles is head gasket leaks, particularly in older models with the EJ series engines. These leaks can lead to coolant loss, overheating, and potential engine damage if left untreated.

How to tell if an engine block is aluminum or steel?

If you have a steel hammer it will leave a big mark on the aluminium but will not mark the steel as much. Along the same lines, hit it with a bit of brass/copper/aluminium. If the punch yields then it is steel. If the block deforms then it is probably aluminium.