If you were to ask a Subaru owner, they may tell you that their world is flat. No, I don’t mean that they think the earth is flat. It’s a clever euphemism for the distinctive engine design used by Subaru: the flat, or boxer engine. The boxer engine is to Subaru what the V-8 is to muscle cars. You may have seen a T-shirt or decal somewhere with the icon below. It’s an illustration of a crankshaft and pistons from a boxer engine.
But there’s so much more to this automaker than its distinctive engine types. Let’s take a closer look at what makes Subaru so special, and what makes it tick as a brand. After that, we’ll look at a few common repairs so you’re prepared to help your customers find the part they need to get their vehicle back on the road again.
Flat Engines vs. Boxer Engines
Subaru engines are often misunderstood. People commonly refer to them as flat engines, but this isn’t the case. There’s one major difference in the construction of these two types of engines.
Both flat engines and boxer engines will have cylinders on either side of a central crankshaft, but the crankshafts are different in each engine type. A flat-engine crankshaft will mount two opposing connecting rods onto a shared crank pin (Figure 1), whereas a boxer engine will mount each connecting rod onto its own separate crank pin (Figure 2).
This subtle difference in construction affects the way the pistons move inside the cylinders. In a flat engine, one piston will move inward while the opposing piston moves outward. In a boxer engine, each opposed pair of pistons will move inward and outward at the same time.
Boxer engines produce significantly lower vibrations when compared to other engine configurations. Since each opposing piston is moving in and out at the same rate and speed, the opposing forces are canceled out. This means that they don’t require counterbalance shafts to smooth out their operation, and the internal components don’t suffer from the same sort of wear and tear caused by vibrations.
Boxer engines offer a number of advantages over other engine styles. (It wouldn’t make sense for Subaru to keep installing these engines into their vehicles if that wasn’t the case.) First and foremost, the boxer engine is incredibly compact. It’s effectively a V-4, with two cylinders on each side of the central crankshaft. This means that the overall length of the engine block is only a little bit over the length of two cylinders.
Boxers also are compact vertically, so they can be mounted lower in the engine bay. This pays dividends when you consider the center of gravity in the vehicle. The engine tends to be the heaviest component in the front of the vehicle. If the engine can be mounted lower in the vehicle, it lowers the center of gravity. This leads to better driving dynamics, better stability in corners and reduced understeer (Figure 3).
Understeer is a phenomenon that causes the vehicle to not turn as sharply as intended. Have you ever put a 24-pack of drinks in the front of a shopping cart, then tried to turn the cart at the end of the aisle? That’s understeer.
As I said earlier, boxer engines produce less vibration than other engine styles, and don’t require any additional counterbalancing to operate smoothly. And last but not least, they produce a truly distinctive exhaust note. Seriously, it’s music to the ears. Well, that may be the car enthusiast in me speaking.
Now, all of these advantages aside, there are a few drawbacks.
The engine assembly is rather complex, both during manufacturing and when rebuilding later on down the road. In an inline or V-style engine, you can place the crankshaft into the main bearings, torque the main bearings, then install and torque the connecting rods onto the crank pins. All of this can be done from underneath the engine with relative ease.
Boxer engines use a crankcase that’s split into two pieces. You can’t access the crankshaft to torque down the connecting-rod caps once the crankcase has been put together. So, the connecting rods must be installed and torqued down onto the crank pins with the crankshaft supported outside of the engine. Then the entire rotating assembly is installed into the crankcase. Or is it?
Nope! The pistons need to be installed onto the connecting rods AFTER the two halves of the crankcase have been bolted together. There are special access holes in the front and back sides of the block that allow you to slide the wrist pins into place (Figure 4). There are a few common issues in boxer engines once they start to age, but we’ll come back to those later on.
Symmetrical All-Wheel Drive
If there’s one other thing that Subaru is known for, it’s the all-wheel-drive system. Known as Symmetrical All-Wheel Drive (SAWD), Subaru has been perfecting the art of driving all four wheels for decades. SAWD was first introduced in 1972 as an optional part-time four-wheel-drive system on the Leone wagon. This early four-wheel-drive system was all-mechanical, and has evolved into the more electronic SAWD system that we know today (Figure 5).
Modern SAWD systems work in conjunction with the vehicle dynamic control, antilock brakes and traction control for optimum handling performance and grip. Subaru has earned a reputation as one of the best vehicles to drive in snowy conditions, or offroad adventuring thanks to the superior grip and stability offered by SAWD. I’m willing to bet that you’ve seen a Subaru Outback with a suspension lift, big offroad tires and a roof rack out on the road. In fact, it’s not uncommon to see Outbacks, Foresters and Crosstreks set up for offroad adventuring out on the road today.
Subaru’s commitment to safety has led to years of industry-leading advancements in both passive and active systems. A precision-engineered, strong vehicle frame will provide maximum protection for passengers in the event of a collision. Subaru’s advanced airbag systems can deploy up to eight airbags, protecting the passengers from forces in all directions (Figure 6).
In other vehicles, the engine and/or transmission may be pushed inside the passenger compartment during a front-end collision. But, thanks to the compact size and placement of the boxer engine, the drivetrain is pushed downward and away from the passengers in a Subaru (Figure 7).
It’s clear that Subaru’s commitment to safety has paid off. A cursory glance at the IIHS website shows strong ratings for all of its current models. In fact, Subaru earned Top Safety Pick or Top Safety Pick+ ratings on the following 2022 model-year vehicles:
• BRZ (Top Safety Pick+)
• Crosstrek (Top Safety Pick)
• Crosstrek Hybrid (Top Safety Pick+)
• Impreza (Top Safety Pick)
• Legacy (Top Safety Pick+)
• Outback (Top Safety Pick+)
• Forester (Top Safety Pick+)
• Ascent (Top Safety Pick+)
The only model missing from this list is the WRX. It appears that the 2022 WRX hasn’t been crash-tested at the time of this writing. Based on Subaru’s track record, I wouldn’t be surprised to see the 2022 WRX also earn its place on this list in the near future. I went back 10 years on the IIHS website and saw consistent top safety-pick ratings for the brand throughout the past decade.
In addition to these strong crash-test ratings, Subaru has pioneered several advanced driver-assistance systems (ADAS) to help drivers avoid collisions whenever possible. The EyeSight system uses a series of cameras to scan the road ahead of you (Figure 8), and apply the brakes if needed to avoid or minimize a collision. Subaru’s DriverFocus system looks for signs of a distracted or drowsy driver, much like an attentive front-seat passenger might do. And of course, Subaru offers other ADAS systems for added safety and convenience including blind-spot detection, rear cross-traffic alert and reverse automatic braking just to name a few.
I’d be remiss if I didn’t mention Subaru’s strong racing heritage. Subaru has proven itself in the racing world by pitting its engineering and manufacturing skills against the competition. And of course, Subaru’s success on the racetrack has led to advancements in its road cars.
If you want to get a closer look into the Subaru racing world, I highly recommend searching for a video series called “Launch Control.” This show follows the Subaru Racing Team USA (SRTUSA) season after season. You’ll see driver profiles and background, vehicle development and the challenges that come along with running a race team.
As with all things that are mass-produced, there are some common failures you should be on the lookout for. If a customer walks into your store with a question about their Subaru, you may be able to help them find exactly what they need to perform the correct repair and keep their vehicle on the road for as long as possible.
Due to the design of the boxer engine, the cylinders are mounted horizontally on either side of the crankcase. This orientation means that any sediment, debris or contaminants that might be present in the cooling system will settle down inside the coolant jackets instead of elsewhere in the system. The same thing will happen with the oiling system. Over time, this can cause the head gaskets to leak, leading to oil and/or coolant consumption, leaks and abnormal smoke from the tailpipe.
This is an issue that has garnered a lot of attention on social media and other channels, but it’s not a guaranteed problem with every single Subaru engine. Routine maintenance such as oil changes and coolant flushes can help to extend the life of the engine and all of its components. There are two types of head gaskets that will be found inside the boxer engine: composite and multi-layer steel (MLS). If the customer removed a composite gasket from their engine, an MLS replacement gasket can be seen as a more robust option. MLS gaskets are more wear-resistant and can offer an extended service life over composite gaskets.
It’s not uncommon to see oil leaking from a high-mileage boxer engine, or any other style of engine for that matter. While not overly common, valve-cover gaskets, camshaft seals and rear main seals tend to be the most likely sources. If the engine-oil level drops between services, but there are no external leaks present, it’s time to look inward. Worn turbo seals, piston rings or a faulty PCV system can cause oil consumption.
The all-wheel-drive system in Subarus can be vulnerable to unintended drivetrain movement or free play. For example, a worn pair of engine mounts could cause the drivetrain to shift from side to side while driving. This places added stress onto other components such as CV axles and bearings. If a customer is in your store asking about a replacement CV axle, try to help them figure out what caused the axle to wear out in the first place. You may be able to help them to treat the cause, not the symptom.
Timing belts and water pumps are routine maintenance items on boxer engines. Replacement intervals vary based on the model and the production year; be sure to check the OE service information for specifics. We suggest selling a complete timing-belt replacement kit with the belt, water pump and all other required components to get the job done.
Finally, be on the lookout for worn, cracked rubber hoses in the engine bay. Years of heat cycling will cause rubber hoses to break down, become brittle and crack. The same goes for plastic components such as radiator end tanks, reservoirs, plastic hose fittings and more.
It seems to me that Subaru has found a winning formula, and the automaker continues to stay true to it. I’m excited to see what the next decade will bring for this pioneering Japanese automaker.