3 Tips on how to choose a Diesel or Petrol car

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kingr
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3 Tips on how to choose a Diesel or Petrol car

Post by kingr »

Petrol or Diesel?

A question asked on our Q/A that has usually been easy to answer had us a bit stumped. Petrol or diesel? Typically, the choice comes down to several factors with either a diesel or petrol engine ticking your desired boxes. Do you want a comfortable, refined stallion or smoky-workhorse? Long-distance cruiser or city commuter? Are you concerned about running costs and resell value? Is fuel economy a priority for you and if not what's your credit card pin? Easy. But South Africa's recent carbon tax bill, emission scandals, unabating fuel prices and the continuous technological improvements of engines have made the lines quite blurred. Add another spanner in the works, the third choice of a hybrid engine. While the global manufacturing giants have introduced electric/hybrid alternatives to their flagship models, the uptake from South Africans has been sluggish. For the average South African motorists, it usually narrows down to three areas; price and running cost, fuel economy and the performance trade-offs - and the choice is either diesel or petrol.

Here are three general tips when considering a diesel or petrol-powered car as well as some essential information regarding legislative changes, the scandals and how it affects you.

Carbon Tax, Corruption, and the Consumer
On the 26th of May this year, the carbon tax bill was signed, and the first phase has come into effect. The controversial bill, which was initially meant to be implemented as early as 2010, had stalled for almost a decade due to mass opposition from fossil-fuel dependent industries facing stifling economic conditions. The bill is the first of many legislative changes to curb carbon emissions and meet the commitments set out in the Paris Climate Agreement. Although the tax is a positive step toward combating climate change, the real tangible impact is starting to be felt by motorists. The carbon tax added 9c/L for petrol and 10c/L for diesel at the pump at the date of its implementation, on top of the increase in fuel levies announced in the 2019 Budget. While the marginal increase may seem innocuous at first, the first phase is scheduled to run until 2022, where more aggressive taxes are set to follow. The carbon tax is set 2% above inflation targets, and that's contingent on whether the Reserve Bank can whither the political storm and keep to its “fiscally conservative” policy. Facing global pressure and running the risk of punitive export duties, the bill aligns with other foreign governments pushing consumers and manufacturers to adopt more fuel-efficient and low-emission producing technology. Which may have South Africa passing similar tax-cuts and "green incentives" for drivers buying eco-friendly cars - and more stringent restrictions on CO2 producing cars that we see in European cities. Keep that in mind, particularly if you're buying a car that you expect to have for a while.

The flip side is how well the big manufacturers have adapted to the regulated market, by introducing smaller, more fuel-efficient and more complex engines while still meeting performance expectations. The fact that the Ford Fiesta has a 3-cylinder 1.0L turbocharged engine that can fit on an A4-sized piece of paper, which produces 92kW of power and a stated 5.0L/100km fuel economy is an astonishing achievement. Likewise, diesel engines have become quieter, smoother, lighter, and better at delivering its power through the higher revs. Diesel engines are the choice of the luxury sport SUVs like the Cayenne and BMW X5d xDrive as well as attractive options for the quiet German sedans like the new G20 BMW 320d. Diesel engines have even crept into the small city-car and sport hatchback segments like the VW GTD (although, admittedly, received a lukewarm reception and is no longer sold in SA). However, the negative effect of increasing bureaucratic barriers through regulation is the temptation to cook the books.

The Volkswagen scandal or Dieselgate, that first rocked the Munich-based manufacturer in 2014 is still reverberating through the industry. Not only did it completely tarnish the reputation of the world's biggest manufacturer, who posted its first quarterly loss in 15-years, it completely warped the perception of drivers and the trustworthiness of the global marquees. Researchers had foreshadowed the repercussions of the fuel emission scandal for over 20 years who observed the cushy relationship between the prominent manufacturers and government emission testing agencies. In 2014, the Environmental Protection Agency flagged 480,000 VW and Audi diesel cars that were sold in the U.S. as having "defective devices" used for measuring emission levels - or in better terms, fraud. After much flip-flopping, VW finally admitted to creating and installing sophisticated software in their cars that could "detect" testing scenarios used by emission agencies and deceptively lower the real NO2 levels to meet acceptable U.S. standards. The result, VW and Audi diesel engines were emitting 40 times the acceptable nitrogen oxide levels on the road than compared in test scenarios. European testing agencies have finally admitted that their methods are outdated, and South Africa is still assessing whether any rigged cars made its way to our shores - so check your VIN number. Despite other big manufacturers assuring the public that no similar practices are taking place, which is about as trustworthy as an officially stated fuel economy, we don't know how far this goes.

With that being said, and the doom and gloom aside, here are three tips when considering petrol or diesel engines with some general rules of thumb.

1. Price and Running Costs
The general rule of thumb when comparing diesel and petrol engines, with regards to price and running costs, is that diesel cars are usually more expensive. Diesel engines tend to be larger, heavier and far more complicated than their petrol counterparts. Diesel engines generate higher torque figures since it operates at higher compression ratios. The reason it has higher compression ratios is that unlike sparkplugs that are used in petrol cars, diesel fuel is ignited by the high temperature of the compressed air inside the chamber. This requires the material used in diesel engines to be highly durable and able to withstand the intense heat and pressure, which increases production cost. Diesel itself is also a highly viscous liquid that requires a more powerful pump as well as a host of other interconnected components. More moving parts means more potential parts that need replacing, and in general, will mean higher running costs.

The BMW 320i petrol engine which is priced at R617,036 is noticeably lower compared to its diesel counterpart the 320d at R649,453. It's also important to note that emission tax on petrol adds R3,036 to the asking price of the 320i compared to R253 on diesel. The Ford Focus 1.5L Trend comes out at more than R20,000 cheaper than the R341,000 diesel TDCi. The general rule is reliable with smaller compact cars but not as applicable once you start looking at bigger vehicles.

The BMW X4 xDrive 20d and BMW X4 xDrive 20i are priced precisely the same at R843, 000 but the emissions tax adds R7,337 to the asking price of the 20i compared to the R3,542 tax on the 20d. The Audi Q5 TFSi Quattro is almost R50,000 more expensive than the TDI Quattro and is approximately R86,000 more expensive in total running costs. Bare in mind despite having equally sized engines; there is a significant performance trade-off between the two.

Ultimately, when it comes to price and running costs, the pros and cons of buying petrol or diesel-powered car is a case-by-case basis. But generally, the price and running costs of diesel alternatives will be higher.

2. Fuel Economy

The fuel emission scandal has questioned diesel's viability and efficacy of being environmentally friendlier fuel. In 1997, after the Kyoto Protocol, diesel was promoted and pushed as the greener alternative to combat rising CO2 levels produced by petrol cars. Diesel engines are more frugal burners, meaning they use less fuel and more air to provide the same performance as petrol engines while emitting less CO2. However, the global drive to curb CO2 levels with diesel fuel overlooked a critical aspect. While diesel engines on average do emit less CO2, it also produces a dangerously disproportionate amount of toxic NO2 - which petrol engines clean through a three-way catalytic converter. With the steep advance in automotive technology, modern petrol engines are generally considered the least pollutive option. Nevertheless, with regards to fuel economy, diesel engines almost always deliver better fuel economy figures and range compared to petrol engines on average.

Take the BMW 220i Sportline auto; it has a claimed fuel economy of 5.0L/100km and a range of 953km. The estimated fuel cost comes to R84, 741 in long term testing. Compare that to its diesel counterpart, the 220d Sportline auto, which has a 4.0L/100km fuel economy and claimed a range of 1 300km, with an estimated fuel cost of R56,160. The fuel economy of diesel adds an interesting dimension to your choice. For example; the petrol Ford Fiesta 1.0T is nearly R30,000 cheaper in price and lower running costs with more kW of power compared to the 1.5 TDCi. However, the 1.5L turbodiesel diesel engine has a better fuel economy, 4.3L versus 3.3L/100km, and goes almost 300km further (1273km claimed range) than the petrol.

However, diesel engines don't seem to hold their value in compact, city cars and strenuous stop-start driving as the general running costs outweigh its fuel economy and range benefits. Diesel utilizes its full potential with long-distance cruising and loadbearing trips.

3. Performance Trade-Off
The most significant difference between petrol and diesel engines is how it generates its power. Diesel relies on compression ignition (CI) which uses the air brought in by the intake valve and then compresses it (increasing the air temperature) to ignite the diesel entering the chamber - petrol engines use sparkplugs. This high compression ratio produces better thermodynamic efficiency, meaning diesel using its power more efficiently. In combination with the high compression ratio, diesel also has a high power density, which is why it has an incredible amount of torque at its disposal. The consequence is that diesel engines are not "rev-happy," and prefer to convert their power to low-rpm torque rather than into speed as petrol engines do. Most diesel engines use turbochargers, but the dreaded turbo-lag has always been a problem.

It all comes down to your driving style and needs. Generally, pull, and load-bearing engines along with long-distance cruising prefer diesel fuel and exciting, high-revving engines like petrol.

Summary

Ultimately, the choice of petrol or diesel is still a matter of preference and needs. Kilowatts versus torque, fuel economy versus running costs, mule or steed. But those clear lines that differentiate the two choices are becoming opaque. The planned tax hikes, failed emission testing methods and rapid improvements in automotive technology will make the question of petrol or diesel more difficult in answering - don't forget about the increasingly affordable third competitor, the hybrid engine.
Kurt #3337

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VAG Fan
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Re: 3 Tips on how to choose a Diesel or Petrol car

Post by VAG Fan »

VW based in Munich? Wolfsburg it is.
In German forums (both VAG and BMW), for that you'd be tarred and feathered on the spot. ;)

For the rest, an interesting read!
Mark R.
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Brenz95
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Re: 3 Tips on how to choose a Diesel or Petrol car

Post by Brenz95 »

As always, an informative article.

Sent from my ANE-LX1 using Tapatalk

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Unobeat
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Re: 3 Tips on how to choose a Diesel or Petrol car

Post by Unobeat »

Informative Read, thumbs up.
THANAS wrote:Mix them together to create Shellstrol, and then mix that with Winstrol to create the ultimate, maximum performance oil for your engine.
panic-mechanic wrote:When I build engines and do stuff like this I do it when there is nobody else around, No distractions, No phone nothing so that you don't forget what you should be doing. It's the little things that make them run right. Anybody can slap a basic bottom end together. that is the easy bit. It's all the little things that makes these builds a success or not.
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kingr
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Re: 3 Tips on how to choose a Diesel or Petrol car

Post by kingr »

VAG Fan wrote: Thu Aug 01, 2019 4:20 pm VW based in Munich? Wolfsburg it is.
In German forums (both VAG and BMW), for that you'd be tarred and feathered on the spot. ;)

For the rest, an interesting read!
:lol: :lol: :lol:

I missed that in editing - we will fix :wink:
Kurt #3337

Current:
- 10" Mx5 NC2 (main daily)
- 12" Toyota Hilux D/C 2.5tdi 4x4 (tow car / vacay)
- 2020 Mini Cooper S Clubman (swambo)
- 80" VW Mk1 2 Door Golf 8vt project 192wkw/314nm

Ex: 07" G5 GTi, 13" ST180, 03" Mk4 2 door 1.8T Stage 2, 07" Velo 1.6, 83" Mk1 GT 2.0 8v MP9, 87" Mk1 1.6 CitiSport, 88" Mk2 2.0 16v, 83" Mk1 GT 1.6 + 40 webers
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