Subaru Forester Diesel Problems: Common Faults

The Subaru Forester diesel combines impressive all-wheel-drive capability, excellent practicality, and economical fuel consumption. However, despite its appealing features, the diesel-powered Forester has developed a reputation for certain mechanical problems that buyers and owners should understand.

The most common Subaru Forester diesel problems include crankshaft failures, diesel particulate filter (DPF) blockages, exhaust gas recirculation (EGR) valve issues, turbocharger faults, clutch wear, and fuel injection problems.

Some of these faults are relatively straightforward to repair, while others can result in expensive engine damage.

Does this mean every Subaru Forester diesel is unreliable? Not necessarily. Many examples have covered substantial distances, particularly when maintained correctly and driven regularly on longer journeys.

In this guide, we'll examine the most frequently reported Subaru Forester 2.0D problems, identify potentially troublesome model years, explain warning signs, and help you decide whether buying a used diesel Forester makes financial sense.

Are Subaru Forester Diesel Engines Reliable?

The Subaru Forester diesel has a mixed reliability reputation.

Its 2.0-litre turbocharged boxer diesel engine, known as the EE20, offers good torque, relatively low fuel consumption, and excellent traction when combined with Subaru's symmetrical all-wheel-drive system.

Unfortunately, the EE20 is not generally regarded as one of Subaru's most dependable engines.

Early versions attracted particular criticism because of reports of crankshaft and bottom-end engine failures. Later versions received engineering improvements, although DPF, EGR, and other diesel-related problems remained possible.

Reliability depends heavily on several factors:

• Engine production year and specification.
• Previous maintenance and oil change history.
• Whether the vehicle regularly completes longer journeys.
• Frequency of interrupted DPF regenerations.
• Driving habits and engine operating temperatures.
• Quality of replacement parts and previous repairs.
• Overall mileage and mechanical condition.

A well-maintained later-model Forester diesel used primarily for motorway driving may provide considerably better ownership prospects than an older example used exclusively for short urban journeys.

Nevertheless, buyers should approach these vehicles carefully because major engine repairs can be expensive.

Subaru Forester Diesel Engine Overview

Subaru introduced its distinctive boxer diesel engine in 2008, offering a different approach from the conventional inline diesel engines used by most competing manufacturers.

Instead of positioning the cylinders vertically, Subaru arranged them horizontally opposite each other.

This design produces a compact engine with a relatively low centre of gravity.

Subaru Forester 2.0D Specifications

The diesel Forester was discontinued with the arrival of the fifth-generation model in 2018 in markets such as Australia.

Therefore, anyone considering one today will generally be shopping for a used vehicle.

Most Common Subaru Forester Diesel Problems

Before examining individual problems, let's compare the principal mechanical concerns.

Not every vehicle will experience these problems, and the table does not represent verified failure rates.

However, it highlights the areas worth investigating during a mechanical inspection.

1. Subaru Forester Diesel Crankshaft Failure

Crankshaft failure is arguably the most serious concern associated with early Subaru EE20 diesel engines.

The crankshaft converts the pistons' reciprocating motion into rotational movement that ultimately drives the wheels.

When it fails, the consequences can be severe.

Some owners have reported cracked or broken crankshafts, damaged bearings, and catastrophic engine failure.

Why Does the EE20 Crankshaft Fail?

Reports involving early EE20 engines have raised concerns about crankshaft durability and stresses within the engine's bottom end.

Possible contributing factors include:

• High combustion pressures.
• Crankshaft or bearing stress.
• Engine block rigidity.
• Lubrication problems.
• Oil contamination or dilution.
• Excessive engine loading under unsuitable operating conditions.

However, not every crankshaft failure has the same root cause, and it would be misleading to attribute all failures to poor maintenance.

Earlier EE20 engine versions are generally considered more vulnerable than later revisions.

Symptoms of Crankshaft Problems

Warning signs may include:

• Deep metallic knocking from the engine.
• Abnormal vibrations.
• Unusual noises under acceleration.
• Low engine oil pressure.
• Sudden loss of power.
• Engine stalling.
• Complete engine failure.

Unfortunately, some failures can occur with little obvious warning.

What should we do?

If an EE20 engine develops pronounced metallic knocking or an oil pressure warning, stop driving as soon as it is safe and arrange professional inspection.

Continuing to operate an engine with a suspected bottom-end failure can make the damage considerably worse.

Is Crankshaft Failure Expensive?

Yes.

A damaged crankshaft can require extensive engine rebuilding or a replacement engine.

Depending on the damage and local labour rates, the total repair bill may approach or exceed the market value of an older Forester diesel.

This is one reason why checking the engine's history before purchasing is so important.

2. Subaru Forester Diesel DPF Problems

Diesel particulate filter problems are another frequent concern.

The DPF captures soot particles from the exhaust gases, reducing harmful particulate emissions.

To continue functioning, the filter periodically needs to burn away accumulated soot through a process called regeneration.

Why Does the DPF Become Blocked?

DPF problems are particularly likely when a diesel vehicle regularly makes short journeys.

For example, driving only a few kilometres to work and returning home may prevent the engine and exhaust system from reaching suitable regeneration conditions.

Repeatedly interrupted regeneration cycles allow soot to accumulate.

Other causes of apparent DPF problems include:

• Faulty exhaust temperature sensors.
• Defective differential pressure sensors.
• EGR system faults.
• Excessive soot production.
• Fuel injection problems.
• Deteriorating engine combustion.
• Accumulated ash inside the filter.

Symptoms of DPF Problems

Common warning signs include:

• Illuminated DPF warning light.
• Reduced engine performance.
• Increased fuel consumption.
• Unusual exhaust smells.
• Frequent regeneration attempts.
• Engine warning lights.
• Limp mode.

A blocked DPF can also place additional stress on other engine components.

How Can We Prevent DPF Blockages?

We can reduce the risk by:

1. Regularly driving longer distances when practical.
2. Keeping the engine properly maintained.
3. Using oil that meets Subaru's exact specification.
4. Investigating repeated regeneration problems.
5. Avoiding unnecessary engine idling.
6. Repairing EGR or injection faults promptly.

A suitable uninterrupted drive may help complete normal regeneration when the owner's manual specifically permits it.

However, a flashing warning or a vehicle already experiencing serious DPF faults may require specialist diagnosis rather than simply driving faster or farther.

A mechanically damaged or heavily ash-loaded DPF cannot necessarily be restored through regeneration alone.

3. Engine Oil Dilution Problems

Oil dilution is an important issue because it can affect engine longevity.

During active DPF regeneration, additional fuel may be injected to increase exhaust temperatures.

Under certain operating conditions, particularly with interrupted regenerations, some fuel can reach the engine oil.

This reduces the oil's ability to lubricate critical components effectively.

Signs of Oil Dilution

Possible symptoms include:

• Engine oil level increasing unexpectedly.
• Oil smelling strongly of diesel fuel.
• More frequent regeneration cycles.
• Changes in engine noise.
• Oil-related warning messages.

An unexpectedly rising oil level is particularly important.

Why Is Oil Dilution Dangerous?

Diesel-contaminated engine oil may provide inadequate protection for:

• Crankshaft bearings.
• Connecting rod bearings.
• Turbocharger components.
• Other moving engine parts.

Over time, this can accelerate wear.

If we discover that the oil level has risen above the permitted limit, the safest approach is to have the vehicle inspected before further driving.

An oil change may be necessary, but the underlying cause must also be addressed.

4. Subaru Forester Diesel EGR Valve Problems

The exhaust gas recirculation system helps reduce nitrogen oxide emissions by recirculating a controlled amount of exhaust gas into the engine.

Unfortunately, EGR components operate in an environment containing soot and deposits.

Over time, carbon buildup can restrict their operation.

Common EGR Symptoms

We may notice:

• Rough idling.
• Hesitation during acceleration.
• Reduced power.
• Increased fuel consumption.
• Engine warning lights.
• Irregular engine operation.

In some cases, EGR control-related diagnostic fault codes may appear.

How Are EGR Problems Fixed?

A mechanic should first confirm whether the problem is caused by carbon deposits, an electrical failure, a sensor fault, or another component.

Depending on the diagnosis, repairs may include cleaning the EGR passages or replacing a faulty valve.

A failed electrical actuator cannot necessarily be repaired simply by removing carbon deposits.

Ignoring EGR problems may increase soot production and contribute to further DPF complications.

5. Subaru Forester Diesel Turbocharger Problems

The EE20 diesel engine uses a turbocharger to improve power and torque.

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Although turbochargers can last for many years, they operate under demanding temperatures and rotational speeds.

Poor lubrication, contamination, worn components, and boost control faults can create problems.

Symptoms of Turbocharger Failure

Warning signs include:

• Unusual whistling or whining noises.
• Poor acceleration.
• Reduced boost pressure.
• Excessive exhaust smoke.
• Increased oil consumption.
• Engine warning lights.

However, these symptoms do not automatically mean the turbocharger itself has failed.

A split intercooler hose, faulty boost sensor, vacuum control issue, or restricted DPF can produce similar symptoms.

Preventing Turbocharger Damage

Regular oil changes are essential.

We should also avoid demanding heavy acceleration immediately after a cold start.

Allowing the engine to reach appropriate operating temperatures before applying high loads can reduce unnecessary mechanical stress.

If the turbocharger develops unusual noises or severe oil leakage, a professional inspection is recommended.

6. Subaru Forester Diesel Injector Problems

Fuel injectors are responsible for delivering precisely controlled quantities of diesel into the combustion chambers.

The EE20 uses a high-pressure common-rail injection system.

As the vehicle ages, injector performance may deteriorate because of wear, contamination, electrical problems, or internal leakage.

Symptoms of Faulty Diesel Injectors

Common symptoms include:

• Difficult starting.
• Rough engine idle.
• Engine hesitation.
• Increased diesel consumption.
• Excessive exhaust smoke.
• Poor acceleration.
• Abnormal combustion noise.

A faulty injector can also affect DPF regeneration and engine emissions.

Are Diesel Injectors Expensive to Replace?

Injector repairs can be costly because the components are precision-engineered.

Before replacing an injector, a qualified technician should perform the appropriate diagnostic checks.

These may include fuel pressure testing, injector correction analysis, return-flow testing, and electrical checks where applicable.

Replacing injectors without verifying the problem can lead to unnecessary expenses.

7. Clutch and Dual-Mass Flywheel Problems

Manual Subaru Forester diesel models may develop clutch and dual-mass flywheel problems as mileage increases.

The dual-mass flywheel helps absorb engine vibrations and smooth the transmission of power.

Because diesel engines produce substantial torque at relatively low engine speeds, these components can experience considerable stress.

Symptoms of Clutch or Flywheel Problems

Signs include:

• Rattling noises at idle.
• Vibrations when accelerating.
• Juddering when pulling away.
• Difficulty changing gears.
• Clutch slipping.
• Unusual noises when starting or stopping the engine.

What Causes Premature Wear?

Potential contributing factors include:

• Frequent stop-start driving.
• Heavy towing.
• Aggressive acceleration.
• Excessive clutch slipping.
• Driving at very low engine speeds under heavy load.

A worn dual-mass flywheel is often replaced alongside the clutch when necessary because the labour involved overlaps considerably.

Nevertheless, not every vibration or rattle comes from the flywheel. Engine mounts and other drivetrain components must also be checked.

8. Subaru Forester Diesel CVT Problems

Some later Subaru Forester diesel models were available with Subaru's Lineartronic continuously variable transmission.

In Australia, the diesel CVT option arrived in 2015.

Unlike a traditional automatic gearbox, a CVT changes its transmission ratio continuously rather than using a conventional sequence of fixed gears.

Potential CVT Warning Signs

We should investigate:

• Jerking or juddering.
• Delayed acceleration.
• Unusual transmission noises.
• Excessive vibration.
• Transmission warning lights.
• Abnormal behaviour when changing between Drive and Reverse.

However, the presence of these symptoms does not establish a specific CVT defect.

Engine performance issues, drivetrain mounts, and other mechanical faults can produce similar behaviour.

How Can We Protect the CVT?

The most important steps are following Subaru's maintenance requirements, using the exact approved transmission fluid, and respecting the vehicle's towing limits.

A used Forester diesel automatic should undergo a thorough transmission inspection before purchase.

9. Glow Plug and Cold-Starting Problems

Diesel engines rely on glow plugs to help improve combustion during cold starting.

As these components age, they may become less effective.

Signs of Glow Plug Problems

Possible symptoms include:

• Difficult starting in cold weather.
• Extended cranking.
• Rough running immediately after starting.
• White smoke during startup.
• Glow plug warning indications.

Nevertheless, cold-starting problems can also result from a weak battery, starter motor issues, fuel pressure problems, or faulty sensors.

We should avoid assuming that glow plugs are responsible without testing.

Replacement may also require care because ageing glow plugs can become difficult to remove.

10. Cooling System and Oil Leak Problems

Cooling system faults and oil leaks are not necessarily unique to the diesel Forester, but they deserve attention on ageing vehicles.

Possible problems include:

• Coolant hose deterioration.
• Thermostat faults.
• Water pump leaks.
• Radiator damage.
• Oil leaks around engine seals.
• Cooling system restrictions.

Why Is Overheating Serious?

Excessive engine temperatures can damage cylinder heads, gaskets, and other internal components.

Warning signs include rising coolant temperatures, coolant loss, overheating warnings, and unusual engine smells.

If the engine overheats, we should stop safely and allow it to cool before further investigation.

Opening a pressurised cooling system while hot can cause serious burns.

Which Subaru Forester Diesel Years Have Problems?

Not all diesel Forester model years have identical engine specifications or mechanical risks.

The EE20 underwent several revisions during its production life.

Subaru Forester Diesel 2008–2010

Early versions are generally considered the most concerning because of reported crankshaft and engine bottom-end failures.

These are particularly relevant to European-market diesel models.

Potential problems include:

• Crankshaft or bearing failure.
• Clutch and flywheel wear.
• EGR faults.
• Diesel injection problems.

We would approach an early example without detailed service records with considerable caution.

Subaru Forester Diesel 2011–2013

Subaru introduced revisions to the diesel engine as production continued.

These models can be more appealing than the earliest examples, although they are not automatically free from serious engine problems.

Important areas to check include DPF operation, oil condition, clutch wear, and engine noise.

A complete maintenance history remains essential.

Subaru Forester Diesel 2014–2015

This period brought further engineering changes and updated emissions systems.

The precise specifications depend on the market and production date.

For the 2015 model year in Australia, Subaru introduced an updated Euro 6 diesel engine and the option of a Lineartronic CVT automatic.

These improvements make some later vehicles attractive, but proper maintenance remains critical.

Subaru Forester Diesel 2016–2018

Later examples generally benefit from more developed versions of the EE20 engine.

However, ageing diesel emissions systems, injectors, turbochargers, and transmission components still require attention.

We should never assume that a newer registration automatically guarantees better reliability.

Which Years Should We Avoid?

The earliest 2008–2010 EE20 models warrant the greatest caution because of their crankshaft failure reputation.

Later models, particularly those with documented maintenance and updated engine specifications, may present a more reasonable purchase.

However, there is no model year that can be guaranteed problem-free.

Subaru Forester Diesel Problems by Mileage

Mileage can provide useful context, but it should never be the sole factor when evaluating reliability.

These are inspection guidelines rather than statistically verified failure intervals.

A diesel Forester with 140,000 motorway miles and excellent maintenance may be in better condition than one with 60,000 miles spent on short urban journeys.

For this engine, driving conditions and maintenance records can be more informative than mileage alone.

How Much Do Subaru Forester Diesel Repairs Cost?

Repair costs vary significantly depending on the country, labour rates, parts availability, and the specific failure.

Subaru Forester 4th Generation Problems: Full Guide

The following table provides a relative comparison rather than fixed quotations.

The most expensive scenario is usually major internal engine damage.

We should obtain an itemised quotation before authorising significant repairs.

For an older vehicle, comparing the repair cost with its current value is particularly important.

Warning Signs Before Buying a Used Forester Diesel

When buying a used Subaru Forester 2.0D, inspecting the vehicle carefully is essential.

Check the Cold Start

Ask the seller not to warm the engine before your inspection.

Listen for metallic knocking, excessive rattling, unusual vibrations, or prolonged cranking.

Some diesel combustion noise is normal, especially when cold, but pronounced mechanical knocking requires investigation.

Check the Engine Oil

Inspect the oil level and condition according to the manufacturer's instructions.

Be cautious if the oil level appears abnormally high, the oil smells heavily of diesel, or the service history shows repeated DPF-related issues.

Check the DPF System

Ask whether the DPF has required repeated cleaning, regeneration, or replacement.

A diagnostic scan can help assess fault codes, recorded regeneration activity, and relevant sensor readings.

Test the Clutch and Transmission

On manual vehicles, check for juddering, slipping, or flywheel noise.

On CVT-equipped vehicles, assess acceleration smoothness, transmission response, and abnormal noises.

Inspect the Service History

Look for evidence of:

• Regular engine oil and filter changes.
• Correct lubricant specifications.
• Timely fuel filter replacement.
• Previous DPF repairs.
• Injector servicing or replacement.
• Clutch or flywheel repairs.
• Engine replacement or major internal repairs.
• Transmission maintenance where required.

Arrange a Specialist Inspection

Ideally, have the vehicle checked by a mechanic familiar with Subaru diesel engines.

A generic inspection may miss some issues specific to the EE20.

A specialist should also identify the exact engine version and investigate any suspicious diagnostic readings.

How to Prevent Subaru Forester Diesel Problems

Although we cannot prevent every mechanical failure, sensible maintenance can reduce the likelihood of avoidable problems.

Change Engine Oil Regularly

Use the oil grade and approval specified for the exact engine and market.

Because oil dilution can occur, monitoring oil condition is especially important.

Drive Long Enough for Proper Operation

Regular longer journeys can help the engine reach normal operating temperatures and support appropriate DPF regeneration.

A diesel Forester used exclusively for very short journeys may face greater emissions-system maintenance demands.

Avoid Heavy Acceleration When Cold

Allow the engine oil and other components to reach suitable operating conditions before placing the engine under high load.

Monitor the DPF Warning Light

Investigate recurring DPF warnings rather than ignoring them.

A repeated warning often indicates that the vehicle requires diagnosis beyond normal regeneration.

Use Suitable Diesel Fuel

Purchase fuel from reputable suppliers and follow Subaru's applicable fuel requirements.

Fuel contamination can damage expensive injection components.

Avoid Overloading the Engine

Respect the vehicle's permitted towing and carrying capacities.

Driving at extremely low engine speeds while demanding substantial torque can also place unnecessary stress on the drivetrain.

Keep Accurate Maintenance Records

Document oil changes, filter replacement, transmission work, and major repairs.

This helps identify recurring problems and improves transparency when selling the vehicle.

Is the Subaru Forester Diesel Good for Long Journeys?

Long-distance driving is one of the situations where the diesel Forester can make sense.

Its combination of torque, all-wheel-drive capability, and economical fuel consumption can be attractive to drivers who travel regularly on motorways or rural roads.

For example, someone who frequently drives several hundred kilometres may be better suited to the diesel engine than someone who only travels a few kilometres around town.

Advantages include:

• Strong low-speed torque.
• Comfortable motorway performance.
• All-wheel-drive traction.
• Practical cabin and luggage space.
• Potentially lower fuel consumption than some petrol alternatives.

However, the potential fuel savings must be considered alongside maintenance expenses.

One major engine or emissions-system repair can eliminate several years of fuel savings.

Subaru Forester Diesel vs Petrol Reliability

Would we choose a petrol or diesel Forester?

The answer depends on driving habits, vehicle condition, and the specific engine.

Petrol Foresters are not immune to mechanical problems.

Some petrol engines have their own oil consumption, cooling, or transmission concerns.

Nevertheless, for drivers primarily making short journeys, a suitable petrol Forester often represents the more straightforward ownership choice.

Is It Worth Buying a Used Subaru Forester Diesel?

A used Forester diesel can still be appealing if it has been well maintained and is available at a reasonable price.

We would consider buying one when:

• The maintenance history is comprehensive.
• The engine runs smoothly without suspicious noises.
• The DPF system functions correctly.
• The oil level and condition are satisfactory.
• No significant diagnostic faults are present.
• The clutch or transmission operates correctly.
• The purchase price reflects the vehicle's age and mechanical risks.

Conversely, we would be reluctant to buy an early EE20 diesel without service records, especially if the engine exhibits knocking, frequent DPF warnings, or evidence of neglected maintenance.

For many buyers, a later petrol Forester may offer a more manageable long-term ownership experience.

Frequently Asked Questions

1. What Is the Most Common Subaru Forester Diesel Problem?

DPF and EGR-related issues are among the commonly reported operating problems, particularly on vehicles used for short journeys.

However, crankshaft failure is the most serious widely discussed concern associated with early EE20 engines.

There is no comprehensive public failure-rate dataset establishing a definitive ranking across every model year.

2. Which Subaru Forester Diesel Years Are Best?

Later models, particularly those produced after the early EE20 revisions, are generally preferable to the first diesel versions.

The updated 2015–2018 models can be worth considering, provided they have strong maintenance records and pass a specialist mechanical inspection.

A newer model year does not eliminate the possibility of DPF, EGR, injector, or transmission problems.

3. How Long Does a Subaru Forester Diesel Engine Last?

A well-maintained Subaru Forester diesel can potentially exceed 150,000 miles (approximately 240,000 km).

Some vehicles may cover considerably more, while others experience major failures much earlier.

There is no guaranteed engine lifespan, and early EE20 crankshaft problems make predictions particularly difficult.

Maintenance, driving conditions, and the precise engine version all matter.

4. Why Does My Subaru Forester Diesel Lose Power?

Possible explanations include a blocked DPF, faulty EGR valve, turbocharger boost problem, fuel delivery fault, or engine management issue.

A diagnostic scan is usually the best starting point.

We should avoid replacing expensive components until the cause has been identified.

5. Should I Avoid the Subaru Forester Diesel?

Not necessarily, but we should approach it carefully.

An early diesel Forester with an uncertain maintenance history presents a greater financial risk than a well-documented later example.

For mainly short-distance driving, a petrol Forester is generally the more suitable option.

For frequent long-distance journeys, a properly maintained diesel can still be a reasonable choice if its purchase price accounts for potential repair costs.

Final Verdict: Are Subaru Forester Diesels Reliable?

The Subaru Forester diesel offers an attractive combination of practicality, all-wheel-drive traction, and efficient long-distance performance.

However, the EE20 engine has genuine reliability concerns that buyers should not overlook.

The biggest Subaru Forester diesel problems include early crankshaft failures, DPF blockages, EGR faults, oil dilution, injector problems, and clutch or flywheel wear.

Some later engines benefited from engineering revisions, but they still require careful maintenance and appropriate driving conditions.

If we're considering a used example, the safest approach is to prioritise documented servicing, a healthy engine, proper DPF operation, and a thorough specialist inspection.

For drivers covering substantial motorway distances, a well-maintained later Forester diesel may still be appealing.

Are Subaru Foresters Reliable in Australia?

For buyers prioritising lower mechanical risk, predominantly urban driving, and simpler long-term ownership, a petrol Subaru Forester is often the more sensible alternative.

Ultimately, the best used Subaru Forester diesel is not necessarily the newest or the cheapest. It's the one with the strongest maintenance history, the healthiest mechanical condition, and a purchase price that realistically reflects its potential repair risks.