If diesel cars are cheaper to run then why haven't they fully replaced petrol cars?

Question

Diesel gives far far better fuel economy than petrol. For example a 1.6 litre petrol engine may only give 35 mpg but a diesel will give over 60mpg! Yes I know diesel fuel costs more but with economy like that you save money.
Also petrol drivers are really hammered with road tax often paying double what diesels cost to tax. Eg a 1.6 petrol car costs £220 a year to tax, compared to only £120 for the same sized diesel.

Car insurance is also much cheaper with diesels.

It's also known that a Diesel engine will last far far longer than a petrol. A petrol engine gets worn after about 130,000 miles but a diesel is still running great well after 250,000 miles. It's because the fuel helps lubricate the engine because diesel is basically an oil.

So why do car manufactures still make lots of expensive to run petrol cars? It seems common sense that diesel is the best type of engine, especially with spiralling fuel prices. I know there are far more diesels now but still petrol cars are in the majority.

Answer 1

Simple answer is a Diesel often isn't cheaper to run overall than a petrol car.



They do better mpg but that's it. Everything else about a Diesel, from the purchase price to the servicing costs and the cost of fixing them is far higher than for a similar petrol engined car.

You need to be doing about 15k+ miles a year for Diesel to start to make sense, and only then if it's a new car.

For secondhand cars at the 5-10 year old, 100k miles mark, Diesels can often work out massively more expensive than the far simpler petrol car.



"It's also known that a Diesel engine will last far far longer than a petrol. A petrol engine gets worn after about 130,000 miles but a diesel is still running great well after 250,000 miles" - That's crap and has been for the last 10-15 years.



"Diesel gives far far better fuel economy than petrol. For example a 1.6 litre petrol engine may only give 35 mpg but a diesel will give over 60mpg! " - It's often nowhere near that. The real world difference is often about 10-15mpg more from a Diesel.

Answer 2

I also prefer diesel, but some of your "facts" are skewed. For example, many petrol engines last well beyond 200,000 miles--and some diesel engines last well beyond 400,000 miles without a rebuild. The 2.8 million mile Greek Taxicab (a 1976 Mercedes-Benz 240d) was a diesel; it averaged over 400,000 between rebuilds



The reason auto companies have not wholly switched to diesel is, many consumers won't buy a diesel automobile. There are a whole host of reasons diesel is less popular with consumers; the biggest one is they're not aware how good diesel fuel economy can be. This is a factor that seems to be changing, but change comes slow.



Another issue is, automakers use Horsepower as a primary means of marketing. A diesel engine generally has a longer stroke than a petrol engine--which means it makes less torque, but it has a lower maximum rpm. Since horsepower is rpm*torque, it works out that a diesel engine makes about 35% less horsepower than a petrol engine of similar displacement. If you want a normally aspirated diesel engine that makes the same horsepower as a normally aspirated petrol engine, the diesel will weigh twice as much. Which makes diesel a poor choice for performance cars, especially when the statistics matter.



Also in the U.S., diesel is considerably more expensive than petrol. At the station right down the road, petrol is $2.99 (cheapest it's been in years) vs. diesel for 3.79. My diesel pickup is still cheaper to drive than a petrol model would be, but it's a very small savings.

Answer 3

The fact of the matter is that modern diesels are hobbled by EU rules, rules that were designed for long distance trucks, not modern cars that spend most of their lives in towns.



For example. I currently drive an old school 5 cylinder 2.5 litre TDI V70 phase 2 & it averages 43mpg. More modern D5 & 2.4D produce 41 & 35 mpg respectively. A backwards step in terms of economy. The older D5's didn't even give you that - 34mpg on average - firmly petrol territory. Both the D5's & 2.4D's are useless on the local runs because they have DPF's (diesel particulate filters - as mandated by the EU) that clog up, unless used on a decent motorway trip. I have no such faults in my old diesel with an engine sourced from an Audi 100.



Small engined petrol cars have now caught up with diesels on most fronts, especially environmental as petrol is simply a cleaner fuel & does not require special filters to clean up it's exhaust.



Modern diesels also have another problem caused by the EU - the diesel additive AdBlue/BlueTec, for trucks this is not a problem, they have an easy to fill tank on the side of the chassis. Cars do not, in fact to refill a car you are looking at a bill of hundreds of £'s. That is a lot considering all you are putting into the cars additive tank is effectively piss & water.



Then there is the stigma of running a diesel, especially on a cold start it sounds like you are driving a tractor, even when you start a modern one.



Petrols cost less to buy in the first place.



Yes, if you do mega mileages on motorways & pull large things modern diesels are make sense, for the driving that most people do, a small petrol is lighter on the wallet.

Answer 4

The engines are heavier, cost more to manufacture, and need more regular maintenance than petrol engines. They also take longer to reach their full operating temperature.



As a result they're not always more economical than a modern small petrol engine when all cost factors are taken into account. For regular short trips they also produce more pollution.



There's also the question of greater noise, especially from cold, lower power output for the same displacement as a petrol engine, and in the UK the diesel fuel is more expensive than petrol.



Petrol engines are also far more adaptable as they are better suited to being incorporated into hybrid-electric designs, and can easily be adapted to run on LPG and bio-ethanol; diesels have too high a compression ration for that.



Diesels used regularly for short trips are also highly prone to clogging up their diesel particulate filters, an essential modern feature to prevent a sooty exhaust, and although they can often be cleared by giving the car a good long run at high speed, it's not always successful and becomes a very expensive replacement issue.



Diesel engines are the primary choice for many vehicle applications, but are not the ideal choice for all cars.

Answer 5

A generator or alternator is essentially an electric motor so a complete series hybrid where the combustion engine drives a generator which then runs a motor basically doubles the electric motor requirement whereas having the electric motor and the combustion engine share some mechanicals allows the electric motor to act as both a source of propulsion and as a generator when needed. This is done rather cleverly in the Prius through planetary gears and a counter torque motor (no actual gear changes, just the appropriate amount of torque to direct the energy along the appropriate mechanical output shaft). A direct mechanical link also allows the large electric motor to be used in starting the combustion engine such that start up is very quick and efficient. The sizing of the combustion engine is to match the steady state power requirements of the car at speed. Basically, the 70 HP engine was selected because that's what it would take to run a car of that size at freeway speeds. To use something significantly less than 70 HP would require running the engine during more dead time to the point of allowing the engine to run even when the car is parked. This would not be suitable in homes with garages nor would it guarantee the power to be always sufficient under all circumstances. E85 is a terrible fuel, to produce one gallon of ethanol from corn it takes the equivalent of 0.8 gallons of gasoline to ferment it hence you're burning 0.8 gallons of gasoline or equivalent (coal for electrical power, etc.) to then burn 1 gallon of ethanol. Bio-diesel makes a lot more sense. But there are very few diesel cars in North America. The high sulfur content of US diesel fuel allowed the American auto makers to be complacent about diesel development since the foreign cars required low sulfur diesel fuel and hence had difficulty penetrating the US market. The consequence is that unlike Europe or Asia, the North American market has very few diesels. Note, that big three backed lobby groups convinced the government to legislate in low sulfur diesel but only when the German auto makers came up with a catalytic converter that removed all the sulfur from the exhaust thereby allowing them to enter high sulfur markets hence the big three could only compete on their home turf with inferior technologies by getting the government to change the rules of the game. Of course, now two of the big three even has the government paying the bills.

Answer 6

Modern diesel engines cost about £1,000 more to build than the equivalent petrol engine, so the cars cost more. The equipment necessary to make a diesel engine meet the latest emissions regulation is to blame, and has also increased the servicing and maintenance costs of diesel engines.



This means that for a low-mileage driver a new diesel car will be more expensive to buy and more expensive to service and maintain than the equivalent petrol car. For a high-mileage driver a diesel may make finance sense compared to a petrol, but the savings are less than they were a few years ago.



Future emission legislation, combined with advances in petrol engine technology such as that in Ford's 1.0-litre EcoBoost engine in the Focus and C-Max, and planned for the next generation of Mondeo, mean that the economic benefits of diesel are diminishing, and manufacturers are preparing for an increase in the proportion of petrol cars sold in Europe over the next few years.

In fact diesel may become virtually non-existent in very small cars in the next 5 years or so, as the costs and weight of a Euro VI compliant engine in a small car (or even a medium car) may not be justifiable by most buyers.



For example, 10 years ago Volkswagen offered a choice of a 1.7 non-turbo or a 1.4 turbo diesel engine in its Lupo A-segment car, but today's equivalent, the "Up!" doesn't offer any diesel engine.



In larger cars, where the cost and weight of the diesel engine are smaller proportions of the overall cost and weight of the car, and buyers typically drive greater distances, diesel is expected to remain dominant in Europe.

Answer 7

Unless you are doing over around 15000 miles a year, which is well above average, a diesel car will be more expensive to buy and run - its a fact, so get over it



On top of that many owners do not want to be using smelly old diesel, prefer the way a petrol engine performs and do not want to listen to the clanking old diesel engine





So why do car manufactures still make lots of expensive to run petrol cars? - because for lower milages they simply are not and because most of us actually like them



Incorrect facts in your question lose you all credability. We have a sporty 1.6 that costs less than £150 a year to tax. There is no point having a diesel that runs to 250000 miles when all of the running gear on the car is well worn out and beyond economical repair well before that.



Have you seen how much it is to replace the dual mass flywheels and anti polution systems in modern diesels? probably not otherwise you would not be coming out with all this rubbish.

Answer 8

Petrol driven cars are usually less noisy and perform better. However, since I replaced my Audi TT FSI with a diesel powered Q3 I have found that these new diesels are much more powerful than they used to be and perform extremely well. With my TT I got around 30mpg but with the Q3 I am achieving about 50 mpg and in all honesty I am getting from A - B just a quick.

Answer 9

There is something in what you say. Diesels CAN be more economical to run if you do enough miles and enough long runs.



The new turbo-diesels give acceleration that is comparable to a petrol engine. They are better at hills than comparable petrol engines too because diesel produces more grunt (torque).



I choose to drive automatic cars for which diesel engines are ideal due to their higher torque at low revs. The downside is that I do not cover enough miles or make enough long journeys for a diesel car to be viable. The initial price plus higher maintenance costs plus shortening the life of the expensive particulate filter makes them a non-starter for me. For me, they would not be cheaper to run .... beside which my wife objects to cars that makes that much engine noise.



Driving schools like diesels because their cars cover many miles and because of diesel's higher torque. It makes the cars slightly harder to stall when clutch control and gear selection is not as good as it could be. Whether the learner would actually be as competent to drive a petrol car after passing their test is questionable, but that's not a criticism of diesel cars.



As a car buyer, I look for the whole-life cost of my car and how pleasant it will be to own. With my current and forecast driving needs, diesel would not be a sensible option.



Car insurance costs are related to risk. As some diesels are slower, less powerful, heavier and less appealing to high risk drivers, it is perfectly plausible that some diesels can be insured for less than some petrol cars. Boring cars are less risky for insurers so they charge less to insure them, whether petrol or diesel.

Answer 10

Depends where you are, in France and Britain they are popular because of fuel economy but in the USA not so much also the thing about them being smelly as diesel is, and at the end of the day if every one drove diesels then our respective governments would hike up the price of diesel and then it would not be so cheap, most of the cost of motoring in Europe is tax of one sort or another

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Answer 12

Because drivers who have always driven petrol cars are prejudiced against them. Older diesels were indeed smelly, noisy and expensive compared to petrol versions. However modern diesels are clean due to exhaust filters, quiet, and much more pleasant to drive. They have much more torque which makes for relaxed driving. VW make a 2 litre diesel that churns out 184 bhp yet still exceeds 67 mpg.

Ok they are a bit dearer than petrols but they last much longer and driving through a puddle doesn't snuff them out.

Answer 13

Many modern petrol cars average 50mpg. Eco cars don't cost much to tax. You need a larger diesel engine to produce the same power as a petrol one and a turbo which is an expensive replacement. They are more expensive to buy and servicing isn't as straightfoward. Diesels are a nightmare to jump start as well, linked with carcinogenic emmisions, older ones are noisy.

Answer 14

They might well have if the government had not increased the tax so much on diesel. Up to 30-40 years ago diesel was much cheaper than petrol, and also potentially more environmentally friendly. However, once diesel cars became more popular the tax was massively increased under some pretext about there being more soot in the emissions.

Answer 15

The question regarding the relative speed can be partially answered by the recent winners of the latest 24hour race at Le. Mans which have been diesel powered

Answer 16

People don't like change. They see petrol as the fuel for cars and diesel as the fuel for buses and lorries. A diesel car is seen as less responsive than a petrol one so they have a bad image. They may be slower at getting from 0 - 60, but for driving down to the shops or even for normal motorway driving, there's no difference. However, it has become a self-fulfilling prophecy. Because they are less popular, people don't want second-hand ones. That means they depreciate more, making them less popular.

Answer 17

All you say is so. My 1.4L diesel car has averaged 52.4mpg since I bought in in mid-2010. The CO2 emissions are only 116g/km, so my VED is only £30. This year's insurance is just under £200.



Diesel engines generate maximum torque at relatively low revs. Mine gives 160Nm at 2000rpm. This is very useful in town driving. It also cruises at 70mph at 2750rpm. On paper, to 30mph, it should out-accelerate a friend's BMW Z4. OK, from then on, I watch it disappearing into the sunset.



However, when diesel cars go wrong, they can be very expensive to fix. I've just paid £1,200 for a new diesel particulate filter (DPF).

Answer 18

Diesel burns not as clean unless u get like a mercedes bluetec