How long til a Diesel become better for MPG

[RobMorris]

Chaps

I'm on the look for a retro daily.
I do 10 miles to work, same back.
The very odd longer drive.
Ave 10k a year

Ive had diesels recently but are they really the best for my buck?
IE I have to pay more for a diesel compared to its petrol equivalent. + Plus the extra few pence on a litre..

My journey takes just over 15 mins

Am I right that a diesel needs to be at full operational temp to benefit from its higher MPGs?
My cars generally just about warm up fully after about 80% of my journey to/from work.

And am I right in thinking a petrol does its standard MPG from cold?

IE I would be better off with the Petrol equivalent?

Cheers!

[Anthony]

Petrol engines run enrichment when cold, so considerably lower MPG until warmed up.

Diesel will likely work out cheaper to run, certainly in terms of fuel and likely including maintenance (assuming an older diesel - newer ones can be a ticking timebomb!) but I guess it depends what value you put on enjoyment - diesels for me are frustrating, but others like them.

To put some figures into the equasion - my 306 HDi works out at 13p per mile in fuel, and my 205 1.9 GTi about 17p a mile (runs on SUL). If you're not doing many miles, there's not a huge amount in it - and chances are my HDi is more economical than most older mechanical TD engines.

[ChasR]

I found that my 205 GTi does around 17-18p a mile. The weight of the car probably has alot to do with it . I know my old Focus 1.6 would probably have struggled to have returned similar figures.

As Anthony said it all depends on the mileage although it can be many other factors as well. I reckon 15,000 miles is probably the breaking point for most people.

As an example when I had my Alfa 1.9 JTD it worked out cheaper than owning a 2.0 Twin Spark (as lovely as those engines are!). Not only was the insurance more expensive on the petrol (to the tune of £200 more), so were other things including tax (£260 vs £170), MPG (the 2.0s are shocking (the Porsche and Stag begin to look frugal in comparsion!)), and servicing costs (Cambelt needs changing ever 36k on a 2.0 with a dial gauge and some special tools meaning quite an expensive you keep totting up the miles; diesels only need it every 60k, spark plugs on the 2.0s are also £££££ thanks to there being 8 platinum plugs).

Add of the the above up and the little extra that the JTD was soon paled into insignificance. The rattly nature could be better though and I do admit that modern dervs come with their issues (although I am still convinced that meticulous servicing can go quite a way in circumventing that).

[Adambt]

I always thought one the main reasons diesels deliver better fuel economy was because of their higher torque lower in the rev range, meaning you don't have to rev it as much therefore use less fuel.
So it probably depends how you drive and on what kind of roads too, If you're sitting in traffic, little difference petrol to diesel, if you're screaming through country lanes, diesel a bit better but not much, if you're sat on the motorway in 5th gear diesel is far superior.

90's diesels are the cheapest to run in my experience had a 306td and a rover 420sdi which both cost me hardly anything in years. When I had a 306 HDI it was brilliant, until it cost a fortune in maintenance and then blew up anyway!

[lordyoung1980]

I'm facing a similar dilemma at the minute, in the not too distant future I'm being made redundant. I.m possibly taking a job 25 miles away, now do i go for a 306 diesel turbo or do i take a small petrol engined car like a Saxo or 106 Pug. Its tough to decide. I'm leaning more towards a diesel as i can chuck in some Veg oil when i can, which i obviously can't do with a Petrol engine.

[composimmonite]

All engines are at their most efficient when hot whether diesel or petrol.
I have a Kenlowe HotStart and plugged in 30 mins for setting off in the morning ensures the best economy (plus working heater) straight away. You can also get diesel powered water pre heaters - Rover 75, Ford Galaxy, Sharan, etc have them as standard if you want to hunt aroudn scrap yards but a lot more expensive to buy new than the Kenlowe

Paul h

[TurboDieselWeasel]

It's a two bladed sword... Modern diesels get stellar MPG - 'retro' diesels - not so stellar.

If I compare my cars:
300CE - 3.0 straight six petrol - 28MPG - 1.55€/l fuel (£1.31) tax: 18.33€/month
300TDT - 3.0 straight six derv - 31MPG - 1.45€/l fuel (£1.22) tax: 40.00€/month

I do about 1000km per month - that's 15.50€ more per month for the (Turbo)diesel. Despite lower fuel costs & more MPG. Same calculation done with 12l LPG @ 0.80€/l & 18.33€ tax/month - now we're talking about savings!

Or all in all: look into alcohol (ethanol, over here ~0.99€/l)) or LPG as fuel. This is where the real savings in fuel costs are at the moment! As a long-term investment a LPG kit will save more money. If you get a car that has allready been converted to run with LPG and works well - winner!

Unless you find a source of free or very cheap WVO or SVO. But WVO will bring it's own problems, such as contamination with water and ultra fine particles which will wear out even the toughest injection equipment over time - and once you need a new injection pump - all savings are gone. I've watched the WVO brigade for some time now (3 years) - even the hardcore WVO-burners admit, that filterint WVO to 1micron is not sufficient and water & acids in the WVO will eventually destroy even the tough Bosch inline injection pumps and nozzles. And treatin the WVO consumes time, money and a lot of space. Centrifugal clearing of WVO is "en voque" at the moment.

But still - I prefere the diesel. I'm a diesel-type of person (hence my user name ), I just like them and the naggling and low-ish revs make me calm. I could sit for hours at the traffic light with the windowsdown and listen to the yatter of the straight six diesel

Last sentence: compare MPG figures of the exact cars that interest you and calculate what they will cost you, based on fuel costs & mileage you do. I think the tax system in the UK is totaly different to what we have (based on cubic capacity, euro norm & fuel type), so that's maybe not such a big downer to you and a diesel might offer actuall savings

Cheers,
Jan

[Deleted]

Probably stating the obvious:

1) Cost of buying the car minus price you expect you'll get when you sell it = depreciation costs.

2) mpg x annual mileage x fuel cost x number of years you're planning to keep it = total fuel cost

3) Number of annual services x servicing cost x number of years = cost for servicing

4) Insurance x number of years

1 + 2 + 3 + 4 = total cost of ownership negating consumables like tyres etc. Compare the two. Profit. Simples.

[optimusprime]

As said before, it all depends on what you want/need .... when i bought my 406 hdi, it was a choice between that and a petrol Saab estate.
My heart said Saab, but my head said Pug .... in the end it was the road tax that swung it, £180 for the pug opposed to well over £200 for the saab.
My daily 'commute' is only 7 miles each way,and i doubt there'd be much in it between the 2.
But last summer we went away, and i got 640 miles out of a tankfull of diesel. Doubt the Saab would have done that.

[joem83]

I'd be more tempted with getting a petrol, mainly because I find diesel's soul destroying lol.

As my commute is 2 miles in non rush hour traffic, I have thought about something like this:
www.ebay.co.uk/itm/Coolant-heater-Engine-pre-heater-Hotstart-ATO-ONE-220-240-VAC-/230895390137?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item35c2700db9

I was going to replace my polo with a Mk4 Golf GT TDi, until I did the sums.
Car was £600-£800 more than a 1.4/1.6 Petrol, insurance was £250 a year more, tax was the same (1.4) £80 more expensive (1.6) & it would only be doing 3k miles a year. Maintenance/parts for the diesel were higher so I gave up on that idea lol/

This is a handy tool for working out fuel cost's
www.fuel-economy.co.uk/calc.shtml

[welshpug]

you really do need the right conditions to make the most of a diesel, especially newer ones, stop start stuff kills diesel MPG more than petrol engines for some reason, however even loaded up the C5 I've been driving does an easy 44 MPG cross country through wiltshire to dorset and back to south wales, sat on the motorway you could push that to over 50, however tottering into town to work and back its under 40, which is the same as I can stretch out of my 205 gti.

[chairchild]

Rover 220SD (not an SDi, those are more upmarket! lol)

Very simple, but one of the best-built cars Rover made, with arguably the best engine ever developed by Rover - the L series

Almost purely mechanical pump (only electronic timing advance, for better economy/emissions) best trim quality, only comparable to the 400's or 600's, and if you like to tinker, you can swap almost any part from a 25 or MGZR onto it (they kinda went downhill budget wise after they made the 200/400 and 600's....)


My last 2 have cost me less than £250, with a years MOT. It's survived hydrolocking (stopped the car from 30mph from locking the engine, with no damage!) And a couple of months ago the cambelt snapped due to me being a cheapskate, swapped the head, and it's still going - no damage to the pistons, only the lifters, and one bent valve

[Anthony]

May 7, 2013 15:27:46 GMT ChasR said:

I do admit that modern dervs come with their issues (although I am still convinced that meticulous servicing can go quite a way in circumventing that).

I'm less convinced, although certainly I agree that newer diesels are less tolerant of neglect than the agricultural lumps of old.

For example, dual mass flywheels and diesel particulate filters are common and often expensive headaches on newer cars which typically aren't found on older engines, and not only are newer diesels more susceptable to electronic/sensor woes than older mechanical pump engines, but the injectors, turbos and inlets (eg BMW swirl flaps) give hassles that rarely existed on older engines.

Knowing the hassles people I know have had with them on new or newish cars (less than 5 years old) I really dread to think what sort of ownership proposition these newer diesels will be when they're 10+ years old with patchy servicing and penny pinching owners.

May 7, 2013 16:08:41 GMT lordyoung1980 said:

I'm leaning more towards a diesel as I can chuck in some Veg oil when I can, which I obviously can't do with a Petrol engine.

You need to make sure that you get the right sort of fuel pump if you intend to run veg, as some types are far more suitable/tolerant than others.

For example, Peugeot XUD engines come with either a Bosch or Lucas fuel pump fitted - the Bosch pumps will take straight veg oil quite happily (although you'd be wise to dillute in winter), whereas the Lucas's must be run with a fair percentage of diesel for longeivity and can (and do) suffer terminal failure on straight veg.

Also, unless you've a source of cheap new veg oil or are happy to mess around with waste oil, it's not actually that cheap any more compared to what it was a few years back. I remember running my old ZX TD on supermarket veg at less than 50p a litre...

May 7, 2013 16:53:45 GMT TurboDieselWeasel said:

Last sentence: compare MPG figures of the exact cars that interest you and calculate what they will cost you, based on fuel costs & mileage you do. I think the tax system in the UK is totaly different to what we have (based on cubic capacity, euro norm & fuel type), so that's maybe not such a big downer to you and a diesel might offer actuall savings

This, although I would add to check against what owners are reporting that they're seeing in the real world, rather than what the manufacturers claim, as the two can be very different!

Here in the UK, our tax system on older (pre-2001) cars is very simple and generally quite a bit cheaper than mainland Europe - below 1549cc is £140 and above 1549cc is £225.

Pre 1973 are tax free.

It's post-2001 that things start getting a bit more complicated and based on emissions.

[bortaf]

Forget MPG, think about repair and servicing costs of a low cost S/H diesel !!!
i get lots and lots of cheapo 10 + Yr old diesels in, all need money spent on them, in the last 2 months it's been a 53 plate skoda 1.9 in for a new clutch and D/M flywheel 2 weeks after purchase, a T reg 306 in for a new lift pump and glow plugs 15 mins after purchace (they really saw him coming !), 2 fiestas and a 206 in for leaking injector seals and new leakoff pipes and the 206 left with the D/M flywheel still rattling cos the owner decided "fook it i'll drive it till it dies", a transit for yet another S/H starter cos the D/M is breaking up and the dust is killing starters, an 807 in cos the it was out of pigs pizz and the particulate filter was blocked, a galaxy in with yet another cracked filter housing, another transit in for a set of injectors (which i had to tow to a specialist to get the dam things coded in before it would start), i could go on.
TBH when you sit down and get the "true" MPG they are usually 3 or 4 MPG ahead on my 25 Yr old P100 BUT i can run on any old fuel, i run it on cooking oil and missfuel dregs (from the cars that needed a new leccy lift pump after missfueling) ;D
IMHO the rover above is about you best bet for cheap motoring or a small petrol car that might be 8 or 10 MPG behind the diesel (even closer on such short journeys) but will cost less to service and repair.

[grez6232]

Current thinking for new cars at least, is that you have to do about 15k miles a year to make driving driving a diesel worth the extra initial outlay (typically around £1500 over equivalent petrol) and the extra cost of diesel.
With older cars where the price difference in purchase price is less, its a relatively simply calculation to work out if diesel is worth the extra. But certainly a good rule of thumb is that you need to be doing at least 10k miles a year. Around that or less, a petrol might be better.

[samg40]

I used to drive a car I built as a track car to work every day, its only 7 miles so I started cycling to work. Now I don’t worry about petrol costs as I don’t do that much mileage and I get fit and lose a bit of weight in the process. Only problem is cycling gets expensive when you start getting into road bikes! I know not everyone can cycle to work but for anyone driving 2 or so miles to work I’d certainly consider it if I were you.

[optimusprime]

May 8, 2013 10:18:10 GMT Anthony said:

May 7, 2013 15:27:46 GMT ChasR said:

I do admit that modern dervs come with their issues (although I am still convinced that meticulous servicing can go quite a way in circumventing that).

I'm less convinced, although certainly I agree that newer diesels are less tolerant of neglect than the agricultural lumps of old.

For example, dual mass flywheels and diesel particulate filters are common and often expensive headaches on newer cars which typically aren't found on older engines, and not only are newer diesels more susceptable to electronic/sensor woes than older mechanical pump engines, but the injectors, turbos and inlets (eg BMW swirl flaps) give hassles that rarely existed on older engines.
.

I have trouble with the DPF on my DAF works lorry, as it only tends to get run around Grimsby all day. the system don't burn it off, so it has to have a blast down the M180 every so often to clear it through.
One of the contributers to demise of Dual Mass Flywheels is drivers pulling away in to high a gear (cos it can) and putting to much stress through it.

[omega]

if its only 10 miles get a push bike! you do it in a hour
or why not a 50cc moped that will do 100 mpg

[scoobypete]

get a petrol one with lpg fitted.....

[daddyglyn]

Really depends on what your using it for I've got an a4 1.9tdi. Wouldn't say there much difference in it with petrol on the drive to work (5 miles) but most weekends am off to a different part of scotland and that where I notice the saving, I can easily do over 300miles in a weekend