Petrol vs Diesel: Which Is Cheaper to Run?
Diesel cars use less fuel per kilometre. But diesel costs more per litre. So which one actually saves you money? Here is a simple breakdown.
Key Takeaways
- Diesel cars use 20-30% less fuel than petrol cars
- But diesel fuel costs R2-R3 more per litre
- Diesel only saves money if you drive more than 20,000 km per year
- Diesel maintenance is more expensive (injectors, turbo, DPF)
- For city driving under 15,000 km/year, petrol is usually cheaper overall
Fuel consumption difference
A diesel engine is more efficient than a petrol engine. A car that uses 9 litres/100km in petrol will typically use 6-7 litres/100km in diesel. That is about 25% less fuel. On a long highway trip, the difference is even bigger.
- Diesel uses 20-30% less fuel than petrol
- Example: Petrol 9L/100km vs Diesel 6.5L/100km
- Biggest savings on highway driving
- In city traffic the difference is smaller
Fuel price difference
In South Africa, diesel (50ppm) is typically R2-R3 more expensive per litre than 95 unleaded petrol. This price gap eats into the fuel savings. The more you drive, the more the lower consumption makes up for the higher price.
- Diesel is R2-R3 more per litre than petrol
- This gap changes monthly with fuel price adjustments
- The gap has been getting bigger in recent years
- You need to drive a lot to overcome this price difference
The break-even point
If you drive less than 15,000 km per year (mostly city driving), petrol is cheaper overall. If you drive 20,000-30,000 km per year (lots of highway), diesel starts saving you money. The break-even is typically around 18,000-20,000 km per year.
- Under 15,000 km/year: petrol wins
- 15,000-20,000 km/year: about the same
- Over 20,000 km/year: diesel wins
- Long-distance commuters benefit most from diesel
Maintenance costs
Diesel engines have more expensive components that can fail: turbochargers, diesel particulate filters (DPF), and fuel injectors. A set of diesel injectors can cost R20,000-R40,000 to replace. Petrol engines are generally simpler and cheaper to fix.
- Diesel injectors: R20,000-R40,000 to replace
- Turbo failure: R15,000-R30,000
- DPF replacement: R10,000-R25,000
- Petrol engines: simpler, fewer expensive parts
- Diesel services are also slightly more expensive
The verdict
If you drive a lot (over 20,000 km/year), mostly on highways, and plan to keep the car for 5+ years, diesel can save you money. For everyone else — especially city drivers doing under 15,000 km/year — a petrol car is cheaper to buy, run, and maintain.
- High-mileage highway drivers: choose diesel
- City drivers and low-mileage: choose petrol
- Consider resale value too — petrol cars sell easier
- Hybrid/electric is becoming a third option
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