Porsche 928 Engine Reliability & Maintenance

Is a 928 Engine Reliable?

The Porsche 928 engine, a V8 powerhouse known for its distinctive front-engine, rear-wheel-drive layout, is generally considered a reliable unit, especially when compared to many contemporary performance vehicles. However, like any sophisticated piece of engineering, its longevity and performance are intrinsically linked to proper maintenance and addressing potential age-related wear. While the core engine design is robust, many 928s are now classic cars, meaning that even with low mileage, components can degrade over time. Therefore, a proactive approach to maintenance is crucial for ensuring continued reliability and enjoying the unique driving experience the 928 offers.

Understanding the 928 Engine's Timing Belt System

The timing belt is a critical component in the 928's engine. Its primary function is to synchronise the rotation of the crankshaft and camshafts, ensuring that the engine's valves open and close at the correct times. The maintenance schedule for the timing belt is paramount, and understanding the differences between early and later models is key.

Timing Belt Replacement Intervals and Risks

The 928 features a timing belt that should ideally be replaced along with the water pump every 50,000 miles. It's important to note the distinction between engine types:

• Pre-1985 (16-valve engines): These are non-interference engines. If the timing belt breaks or slips, the valves will not be damaged, though the engine will cease to run. While catastrophic failure is less likely, teeth can still shear off, leading to belt slippage and the same outcome.
• 1985 and later (32-valve engines): These are interference engines. A broken or slipped timing belt in these models will result in bent valves, a significantly more expensive repair. These later engines are equipped with a warning light that monitors belt tension, providing an early indication of potential issues. It is vital that this warning system is not bypassed, as doing so can lead to severe engine damage.

Even with low mileage, the age of the rubber belt is a critical factor. A belt that is 5-7 years old can fail due to material degradation, regardless of its mileage. Therefore, replacing the timing belt based on age is as important as replacing it based on mileage. The cost for a timing belt, pulley, and water pump replacement typically averages around £1,000 in a reputable workshop.

The Importance of Belt Tensioning

Contrary to some misconceptions, the 928 timing belt system is not self-tensioning. While there is a tensioner that accounts for minor belt stretch and temperature fluctuations, periodic re-tensioning is necessary. The tensioner itself relies on oil for damping and heat transfer. Neglecting this can lead to premature belt wear or failure. If the tension warning light illuminates, it's crucial to investigate the cause immediately, which may involve checking the oil level in the tensioner or inspecting the tensioner itself for leaks or damage. Using a tension gauge is the only accurate way to set the correct belt tension; attempting to adjust it by feel or guesswork can lead to over-tightening and damage to pulleys and guides.

Troubleshooting the Timing Belt Tension Warning Light

The timing belt tension warning light can be triggered by several factors:

• Low oil in the tensioner: This can be topped up with SAE 90 gear oil using a syringe or oil can.
• Worn tensioner seal or boot: The rubber boot can become brittle with age and crack, leading to oil loss and improper damping.
• Loose electrical connection: The sensor is a simple switch, and a poor connection can trigger the light.
• Actual belt looseness: This is the most serious cause and requires immediate attention.

A common troubleshooting step involves disconnecting the sensor wire and cranking the engine. If the light comes on, the wiring and warning unit are likely functional. If it doesn't, the issue lies within the circuit or the belt tension.

The 928 Water Pump

The water pump is often replaced concurrently with the timing belt. This is due to the significant labour overlap; accessing the water pump requires removing the timing belt covers. While a water pump can theoretically last for two timing belt changes, replacing it at the same time as the belt is a common and recommended practice to avoid the expense of separate labour later. Signs of a failing water pump can include coolant leaks from behind the timing belt covers, or noise from the pump bearing. A failing water pump bearing can also affect timing belt tension, posing a risk to the engine.

Motor Mounts: A Crucial Comfort Factor

The engine mounts in a 928 are hydraulic and designed to isolate engine vibrations from the chassis. Over time, the fluid within these mounts can leak out or evaporate, causing them to lose their effectiveness. This leads to a noticeable increase in vibration felt within the cabin, making the car feel less refined. Worn mounts allow the engine to settle, potentially bringing metal-to-metal contact between the engine and the chassis. A simple check involves measuring the gap between the mount and its safety stop; if you can fit a finger in the gap, the mounts are likely worn. Replacing motor mounts is a labour-intensive job, often requiring the removal of the steering rack and cross-member. While challenging, the improvement in driving comfort can be significant.

Cooling System Health

The 928's cooling system is complex and vital for maintaining optimal engine temperature. Several components can contribute to cooling system issues:

Coolant Leaks and Overheating

Coolant leaks can originate from various points, including hoses, the water pump, heater core, or even a blown head gasket. A common cause of coolant loss without obvious puddles is evaporation from hot surfaces, such as the engine 'V' or the radiator/heater cores. The characteristic sweet smell of evaporating antifreeze is a strong indicator of a leak. If the coolant light illuminates and the temperature gauge rises rapidly, it indicates a significant cooling system problem, and driving the car is not recommended. It's often advisable to replace all coolant hoses simultaneously if one shows signs of deterioration, as the others are likely to be of similar age and condition.

Thermostat Functionality

The 928's thermostat operates differently from many conventional vehicles. It's essential for proper engine warm-up and temperature regulation. In certain conditions, it blocks flow to the radiator while allowing bypass flow within the engine block to ensure even heating. Removing or tampering with the thermostat is strongly discouraged, as it can lead to overheating. Drilling small holes in the thermostat flange is sometimes done to aid in air bleeding, but excessively large holes can prolong warm-up times.

Coolant Level Sensor

The coolant level warning light system involves both a level sensor and a pressure switch. If the level light is constantly on, it could indicate a faulty sensor, wiring issue, or a problem with the control unit. Testing the sensor and its connections is a common diagnostic step.

Oil Changes and Oil Quality

While many owners opt for frequent oil changes (every 3,000 miles) using high-quality synthetic oil like Mobil 1, the manufacturer's recommended intervals are often more generous. However, given the cost of potential engine repairs, using a quality oil and changing it more frequently than the absolute minimum can be seen as cheap insurance. Harsh driving conditions, such as frequent short trips where the engine doesn't reach optimal operating temperature, or driving in dusty environments, warrant more frequent oil changes to remove moisture and contaminants.

Clutch and Transmission Reliability

The 928 featured different transmission options throughout its production run. The earlier transmissions are generally robust, capable of exceeding 100,000 miles with proper care. The introduction of the Borg Warner transmission in 1985 offered smoother operation and reduced the issue of premature synchro wear. While the later S4 models introduced a single-disc clutch system, the earlier dual-disc systems are considered very reliable and capable of handling high power outputs. The hydraulic clutch system may require attention before the clutch itself wears out.

Other Considerations

Harmonic Balancer Removal

Removing the harmonic balancer (vibration damper) during timing belt replacement can be challenging due to its press-fit nature. While pullers can be used, caution is advised to avoid damaging the rubber element. Soaking with penetrating oil and careful prying are often successful methods. If the balancer is damaged, replacement can be costly.

Backfiring and Induction Issues

Backfiring, particularly during cold starts, can be a serious issue, sometimes leading to damage to the airbox and induction system. This can be caused by ignition timing issues, a stuck intake valve, or a malfunctioning fuel injector. Diagnosing the root cause is essential to prevent recurrence.

Idle Speed Adjustment

Idle speed on the 928 can typically be adjusted via a screw located near the throttle body. It's crucial to ensure there are no air leaks in the intake system before adjusting the idle, as these can significantly affect engine performance and idle stability.

Carbon Cleaning

While some engine cleaning services claim to remove carbon deposits, the 928 engine generally does not suffer from excessive carbon build-up unless subjected to poor tuning or significant oil consumption. Routine maintenance and proper engine operation usually keep carbon deposits to a minimum.

Porsche 928 Engine FAQ

Q1: Is the 928 engine generally reliable?

Yes, the 928 engine is generally considered reliable, but age-related wear and the need for consistent maintenance are crucial factors.

Q2: How often should the timing belt be replaced?

The timing belt should be replaced every 50,000 miles or every 5-7 years, whichever comes first, due to the risk of age-related degradation.

Q3: What happens if the timing belt breaks on a 1985 or later 928?

On these interference engines, a broken timing belt will cause bent valves, leading to significant repair costs.

Q4: Should I replace the water pump when changing the timing belt?

It is highly recommended to replace the water pump at the same time as the timing belt due to the shared labour costs and the pump's critical role in the cooling system.

Q5: What are common signs of worn motor mounts?

Increased vibration felt in the cabin, especially at idle or low speeds, is a primary indicator of worn motor mounts.

Q6: How do I check the timing belt tensioner?

The tensioner requires oil and proper tension. If the warning light is on, check the oil level, look for leaks, and ensure the tensioner is functioning correctly. Using a tension gauge is the definitive method.

Q7: Can I drive my 928 if the coolant light comes on?

No, if the coolant light comes on and the engine temperature rises, it is unsafe to drive the car. Pull over immediately and investigate the cause.

Q8: Is it necessary to have a thermostat in a 928, especially in warmer climates?

Yes, the 928's thermostat plays a critical role in engine temperature regulation and must be present for correct operation, regardless of climate.

Q9: What is the typical cost of a timing belt and water pump service?

This service typically costs around £1,000 at a reputable independent specialist.

Q10: How often should I change the engine oil?

While manufacturer intervals can be extended, changing the oil every 3,000-5,000 miles or 6 months, whichever comes first, is a wise preventative measure for preserving engine health.

In conclusion, the Porsche 928 engine offers a blend of power and engineering sophistication. By understanding its specific maintenance requirements, particularly concerning the timing belt, cooling system, and engine mounts, owners can ensure the long-term reliability and enjoyment of these iconic vehicles.

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