Mechanic Tips

Diesel vs Petrol Engines: Maintenance and Performance Comparison

When it comes to choosing between a diesel or petrol engine, there are several factors to consider regarding maintenance and performance. With advancements in technology, both engine types have become more efficient and reliable over the years. However, there are still key differences that drivers should be aware of. This article examines the pros and cons of each engine to help you decide which is better suited for your needs.

Maintenance Costs

One of the biggest considerations is the cost of maintenance and repairs. In general, diesel engines tend to require less frequent servicing than petrol engines. The service intervals are typically longer, often ranging from 10,000-20,000 miles between oil changes compared to around 5,000-10,000 miles for a petrol engine. Diesels also do not require spark plug changes or ignition timing belt replacements, which are common maintenance tasks on petrol cars. This lower maintenance requirement translates into lower costs over the lifetime of a diesel vehicle.

However, the parts and labor for diesel engine repairs tend to be more expensive than petrol when they are needed. Components like the fuel injectors and turbochargers are more costly to replace on a diesel. This evens out the playing field in terms of overall maintenance and repair costs over the long run.

Fuel Efficiency

When it comes to fuel consumption, diesel engines are hands-down more efficient. The precise difference depends on the vehicle, but a diesel will typically achieve 15-30% better fuel economy than the petrol equivalent model. This efficiency advantage stems from diesels having a higher compression ratio in the engine and the higher energy density of diesel fuel itself. For high-mileage drivers, the improved fuel efficiency can lead to significant cost savings in the long run.

On the other hand, modern petrol engines have narrowed the gap somewhat with advances like direct fuel injection, turbocharging and variable valve timing. Petrols still lag behind diesels, but are not as far behind as in the past. For lower mileage drivers, the fuel savings of a diesel may not offset the higher upfront vehicle cost.

Performance Differences

The performance characteristics of diesel and petrol engines also differ in a few ways. Diesels provide stronger low-speed torque, which gives them quicker acceleration from a standstill. The abundance of torque also allows diesel engines to handle heavier loads and towing more efficiently. However, petrol engines tend to have a higher maximum rpm and thus higher top speeds. Petrol’s lighter weight and higher revving abilities also make them more suited for sporty driving.

Modern turbocharged diesels have helped improve power and throttle response at higher rpms, while turbo petrols provide increased low-end torque. But in general terms, diesels still favor traction at low speeds, while petrol engines achieve better performance at higher speeds. Drivers should consider their specific performance needs and driving style.


In the past, diesel engines had a reputation for longevity thanks to their iron block design and lower rotating speeds. However, modern diesel engines have more complex fuel injection and emissions components that impact reliability. Turbochargers and particulate filters require careful maintenance in diesels, which are less of a concern for petrol engines.

When maintained properly, both engine types can reliably reach over 200,000 miles. But on the whole, petrol engines tend to need fewer repairs and have lower rates of failure past the 100,000 mile mark according to consumer surveys. For buyers focused on durability, petrol is the safer bet.

Environmental Impact

One area where petrol engines have an advantage is lower emissions output. Diesel exhaust contains higher levels of nitrogen oxides (NOx) and particulate matter, which have a negative impact on air quality. Diesels still produce less carbon dioxide (CO2), but stricter emissions standards have helped petrol engines catch up.

Many modern diesels also require diesel exhaust fluid (DEF) or AdBlue to meet emissions regulations. This is an added maintenance task and cost that petrol vehicles avoid. As emissions laws become more stringent, diesel’s higher polluting emissions are becoming a bigger liability.

Noise Levels

The characteristic “diesel clatter” at idle and lower speeds makes diesel engines run louder than comparable petrol engines. The combustion noise is inherent to diesels due to their higher compression ratios. Dampening materials and engine mounts have reduced the noise somewhat, but diesels are still louder overall. This may be a consideration for buyers who prefer quieter cabins.


In summary, diesel engines hold advantages for fuel efficiency, torque, and long-term maintenance costs. But petrol engines are cheaper to buy upfront, emit less pollution, and often have greater performance capabilities. For most buyers, the decision ultimately depends on your specific needs and priorities. High-mileage drivers can benefit most from a diesel’s fuel savings, while petrol suits those who prioritize affordability and engine refinement. Speak to a knowledgeable mechanic to weigh the pros and cons before deciding. At SNC Automotive, our technicians have over 20 years experience with diesel and petrol engines. Visit our workshop in Brendale to get trusted advice on selecting your next car engine.


What type of engine requires less frequent maintenance?

Diesel engines generally require less frequent maintenance than petrol engines. Diesel service intervals are typically around 10,000-20,000 miles between oil changes, compared to 5,000-10,000 miles for petrol engines.

Which engine has better fuel efficiency?

Diesel engines are significantly more fuel efficient than petrol engines. A diesel will typically achieve 15-30% better fuel economy compared to a similar petrol engine vehicle.

Which engine is better for towing or hauling heavy loads?

Diesels are better suited for towing and hauling due to their high torque output, especially at low rpm. The abundant low-end torque helps diesels handle heavy loads efficiently while accelerating or going uphill.

Which engine option emits less pollution?

Petrol engines have lower emissions overall compared to diesel. Diesel exhaust contains higher levels of nitrogen oxides and particulate matter, which have a greater impact on air quality. Stricter standards have helped close the gap, but petrol engines remain the cleaner option.

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