Detailed Analysis - Sonet 1.2 Petrol vs Diesel - Should You Buy The Kia Sonet Diesel?

Update (Feb 16, 2022): Please refer to the latest mileage and fuel cost comparison of the Kia Sonet 1.2L normal petrol and 1.5L turbo diesel models to help you decide which one is right for you:

Kia Sonet Petrol Or Diesel? Mileage & Running Cost Comparison

This knowledge will help us objectively answer, once and for all, which engine you should buy and why. We’ll compare the 1.2L normal petrol engine of the Sonet, which is available in HTE, HTK and HTK Plus variants and compare it with the Sonet diesel.

Kia Sonet Petrol vs Diesel - 1.2L Normal Petrol vs 1.5L Turbo Diesel

Let’s start off with comparing the prices of the lower variants of the Kia Sonet 1.2L normal petrol and 1.5L turbo diesel engine.

Kia Sonet 1.2L Petrol vs 1.5L Diesel - Upfront Cost

The price difference between the Kia Sonet 1.2L petrol and 1.5L diesel options varies between Rs. 1.04 to Rs. 1.4 lakh. The lower two variants, HTE and HTK, are on the expensive side and the higher HTK Plus trim is only Rs. 1.04 lakh. Since the on-road price will vary from state to state, we are only considering the ex-showroom price difference. But, you also have to take into account the on-road price difference between the variants you’re considering.

Based on our variants explained recommendation, the HTK Plus is the variant you should consider if you want a decent amount of kit and value for money. The price difference between petrol and diesel variants is also quite low, which makes the HTK Plus diesel that much more attractive proposition.

For our calculations, we’re considering the HTK Plus variant only.

Kia Sonet 1.2L Petrol vs 1.5L Diesel - Insurance Cost

Besides the upfront cost difference between petrol and diesel engines, there’s also going to be a difference in their insurance costs. The Sonet variant with the diesel engine is more expensive, therefore, it’ll also cost more to insure. Expect a Rs. 4,000 - 7,000 price difference in the first year. The difference will also vary based on the insurer and add ons you choose. But, for a 7-year ownership period, let’s assume an average of Rs. 4,000 per year as the car’s value will also depreciate with time. So, the diesel car will end up costing you about Rs. 28,000 more for this duration.

Kia Sonet 1.2L Petrol vs 1.5L Diesel - Performance

The Sonet 1.2L petrol has an ordinary performance judging by its torque-to-weight and power-to-weight ratio figures. The diesel engine makes 17PS more power and 125Nm more torque than the 1.2L normal petrol of the Kia Sonet. If each unit of horsepower and torque is worth Rs. 500, this performance gap between these two engines alone is worth Rs. 71,000.

The diesel engine also has a 6-speed transmission, which will help it cruise at relaxed RPMs on the highways but without the extra bottom-end torque, this cruising is not possible. So, we’re not giving it any additional value. Moreover, this tall 6th gear will also help it deliver better mileage while driving on the highways but that advantage will be covered in the fuel costs. So, we’re skipping it in this subsection.

With this additional torque, the turbo diesel will be much easier to drive in the city at low RPMs as you can get good acceleration without downshifting or revving the engine.

To warp up the performance part, the Sonet 1.5L diesel engine comes out on top in this section earning an advantage of Rs. 71,000 over the 1.2L normal petrol engine.

Kia Sonet 1.2L Petrol vs 1.5L Diesel - Fuel Cost

Calculating fuel cost is tricky because the price difference between petrol and diesel varies drastically from one state to another. So, we'll calculate the figures for a 70,000km ownership duration with a price difference of Rs. 0, Rs. 5 and Rs. 10 between the two fuel types. Then you can use the closest figure based on your city fuel prices.

Moreover, the real-world fuel efficiency also varies drastically based on factors like wheel alignment, tyre pressure, vehicle maintenance, driving style, traffic, weather and vehicle load.

To keep things even, we’re going to use the official claimed mileage figures. The Sonet 1.2L petrol claims to deliver 18.4kmpl while the Sonet diesel manual has an official mileage figure of 24.1kmpl.

#1 - Rs. 10 Price Difference Between Petrol And Diesel

Let’s say the petrol costs Rs. 90 and diesel costs Rs. 80. With the fuel prices heavily in diesel’s favour, the fuel cost per kilometre tips Rs. 1.57 in diesel’s favour. Over a driving distance of Rs. 70,000, this adds up to Rs. 1.1 lakh. That’s quite a substantial saving in such a short period.

#2 - Rs. 5 Price Difference Between Petrol And Diesel

If petrol costs Rs. 85 and diesel costs Rs. 80, then the per kilometre cost advantage in diesel’s favour is Rs. 1.3. So, for a 70,000km ownership period, the diesel car will save you about 91,000. That’s still a decent chunk of money.

#3 - Rs. 0 Price Difference Between Petrol And Diesel

If both fuels cost Rs. 80, then the diesel engine’s better fuel efficiency figure only gives an advantage of Rs. 1.09 per kilometre. So, over a course of 70,000km, the diesel engine will save you Rs. 76,000.

Kia Sonet 1.2L Petrol vs 1.5L Diesel - Routine Maintenance Cost

The diesel engine has more components in it like a turbocharger, intercooler, direct fuel injectors, high-pressure fuel pump, and a few others. The diesel engine also runs at higher stress levels than a normal petrol engine. Thus, it will have higher maintenance costs. Here’s the routine maintenance costs of the 1.2L normal petrol and 1.5L turbo diesel engine of the Kia Sonet:

NOTE: These prices are as per routine maintenance schedule and declared by Kia Motors. GST is not included in the costs. Even without the GST, the above-mentioned service costs should give us a fair idea of how much more the diesel engine might cost to maintain compared to the 1.2L petrol for a period of 70,000km and 1.0 lakh km.

Based on these figures, we can see that the petrol engine will cost about Rs. 5,000 less to maintain for an ownership period of 70,000km.

Verdict - Kia Sonet 1.2L Petrol vs 1.5L Diesel - Should You Buy The Kia Sonet Diesel?

Based on our comparison, the diesel engine is objectively coming out on top and justifying the price difference with better performance and mileage. It’s saving you Rs. 44,000 during a 7-year / 70,000km ownership period if the diesel in your city is Rs. 10 cheaper than petrol. If this price difference drops to Rs. 5 and Rs. 0, then for the same duration, you will end up saving Rs. 25,000 and Rs. 10,000.

However, there are still a few things you should consider:

1. Refinement: The diesel engine will be noisier than the 1.2L 4-cylinder petrol engine at regular city speeds.
2. Registration Cost: The registration cost for the diesel engine in your city may tip the scales in the petrol engine’s favour.
3. Loan Amount: We haven’t considered the additional interest you might incur if you’re taking a loan and have to increase the loan amount of tenure to accommodate the Sonet diesel in your budget. Please factor that difference in the ‘upfront cost’ section to get a realistic cost difference.
4. Bigger Price Difference: If you’re considering the lower variants, the higher cost difference will also make the Sonet diesel more expensive because of the bigger ex-showroom price gap.
5. More Driving: If you drive more or intend to hold on to the car for longer, then the diesel engine may turn out to be even cheaper in the long run. We have laid out the cost per km difference for different fuel prices between the two engines to help you calculate the difference based on your expected ownership mileage. Similarly, the table for maintenance costs includes the routine maintenance costs for up to 1.0 lakh km so you can gauge how it’ll affect your bills if you intend to clock more miles.
6. Depreciation: We haven’t included the resale cost as it’s difficult to predict how the market conditions may evolve during this decade. It may drastically affect the diesel cars’ resale price or even increase the demand.
7. Need For Speed (Err. Performance): Based on your usage, the performance of the diesel engine may hold more or less value. For example, if you frequently drive on open roads and highways, then the 1.2L normal petrol engine may feel stressed consistently maintaining triple-digit speeds. However, if you mostly drive in the city, then this engine can offer adequate performance.