Petrol v deisel in a small car
 

iF you were to buy a smallish eurobox as a new car (not necessarily new) what would you get the most mpg out of, petrol or deisel. I know something like the 1.4tdi in the Seats and Fiats etc is super economic but a sweet little 1.0 petrol can run on fumes almost. Also an estate would prob tip the balance in the aero dept. The reason I ask, is quite a few people on here seem to run these metro jobbies. i read somewhere that they are a suzuki swift (petrol) and seem to get v.good milage. Are they the eco car of choice? or are there just a lot about?

Diesel has about 10% more energy per gallon than gasoline, so these engines inherently get better mpg. Considering how common it is to mix ethanol with gasoline, the energy content is even more in favor of diesel (ethanol containing roughly 2/3 the energy of gasoline). On top of that, the diesel engine is more efficient due to higher compression, lower pumping losses, and lower RPM.

The general rule of thumb is that a diesel will get about 30% better mpg than the gasoline counterpart. Just compare the various flavors of Volkswagen Jetta.

Keep in mind, in the US, diesel is currently 8% more expensive than gasoline and buying a diesel model car is more costly than the gasoline counterpart. It would take quite some time to recover that additional expense.

Assuming 12k miles traveled per year, gas @ $3.83 and diesel @ $4.12, with a $4,000 price difference between Jetta gas and Jetta diesel, it would take nearly 13 years to recover the extra expense of the diesel. That doesn't even factor in the interest you could have earned by investing the $4,000 you saved, or didn't make interest payments on. You would break even about the time the car is retired.

Auto makers don't like trying to sell small diesel cars in the USA, partly because in the 1970's the US automakers tried to make diesel engines that were based off gasoline engines and their vehicles suffered catastrophic failures.
Geo Metro's are popular on here because they are one of the most common cars that was sold in the US with a 1 litter engine, so while a lot of us would love to have a small diesel car, the only way we can get one is to buy a VW or to import something that is 20 years old or older from some other country that sells small diesel cars, reason for the 20 year old figure is that at that point the import regulations are not as strict and while some people do buy diesel VW's, we don't even have very many options here, the VW golf, Jetta and Passat are really your only choices and even they have a spotty reputation because here in the USA we were getting VW's that were made in Mexico for a while with more electrical problems then you can count, timing belt failures are still an issue and repair costs are some of the highest of any vehicle sold here.

I would go with diesel. The added benefit is, if you ever run out of fuel, just drain some random car's oil pan and voila! You're back on the road again.

There are only a very few new cars that I'd consider buying and one would be a VW Up! diesel. Sadly VW continues to smite us- not only denying the Mk3 Scirocco but also the Polo and Up!, it's a miracle we even got the MK6 Golf R.

Anyway, people choose Geo Metros because they're about the best bet for cheap fuel economy in the country.

I'd say it's much more dependant on how you use it.

Diesels don't appreciate short journey or city driving. They take longer to warm up and newer cars have DPF (diesel particulate filters) that require high engine temps to clear themselves. A serious of short journeys will see you clog the DPF. Diesels have also become far more complicated in the hunt for sales. Turbos, DPF and Dual Mass Flywheels are all expensive items you won't find on many petrol equivalents (though small turbo petrols are increasingly common), and other items like injectors are far more expensive on diesel engines.

However, if you're doing big mileage, over 20,000 miles p/a say, then a diesel make increasingly more sense financially. But you'd still have to consider selling it on before the end of the warranty period.

Hey, why not just have the best of both worlds. Fill up your tdi on gas and your gas car on diesel! The one that survives is the winner.

Omnivores my ass...

The OP lives in the UK, no? This means they aren't constrained to only VW diesels. :p

I know he lives in the UK. But DPF, DMF and expensive fuel systems are not constrained to just VAG motors.

And apart from that, VAG Europe cars aren't seen as unreliable, most the taxi drivers in my area at least drive Skoda Octavia/Superb and Audi A4.

...uh, didn't notice my use of the 'weasel-word' "...almost..." did you?

"...diesels are almost omnivorous, while gasoline engines choke on almost anything but petrol."

Sorry, I assumed you were referring to water and pixie dust.

Tell me about it :(

I'm seeing my share of troubles with a PSA / Volvo engine and assorted accessories.


I'd advice against a diesel.
The way things are looking, the "clean" diesels with DPF etc. could well become the most harmful of them all !

How about natural gas ?
Cleanest fossil fuel, with potential to get it from biological , renewable sources as biogas ?

Could come cheap in the form of some second hand Fiat .

Indeed.
Modern diesels have become very picky in their fuel choice.
Matter of fact, with today's DPF systems, they can't even take high biodiesel content any more !

In Germany, it's nearly killing part of the biodiesel industry as the cars that could take biodiesel (RME in Germany) are slowly disappearing.
It's only the 5% mix in regular diesel that keeps them going - but it takes 20 cars to get to the fuel needs of just 1 car running at 100% BD !

Uh, diesel engines and dumkoph gobberments are two totally different things, although they both DO seemingly work under high-compression ratios: much IN, much ado OUT.

Is there any sort of easy checklist for converting/modifying modern diesels to run on WVO/WMO?

If it's got a DPF, you can forget about using biodiesel (RME, FAME - either as 100% or high-% blends), and vegetable oils.

You have to go for older diesels without, or pray that they start converting them to run with a fifth injector in the exhaust to enable the DPF.

Even then, biodiesel has its effects on engines... you can actually see valve recession on some engines when running biodiesel. Straight veggie oil is a little better, but it's solid at low temperatures (which is why they convert it to biodiesel). It still washes in to the engine oil over time, requiring more oil changes.

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Gasoline engines can run run E85, E100 or LPG (with different injectors). Same problem, LPG... valve recession... but it depends on the motor.

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Hear, hear... DMFs are a pain in the ass. At least there are some companies selling SMF conversions, as long as you can put up with the clatter...