Author Topic: The great diesel con... (Read 6584 times)

HardRockCamaro · « **on:** November 18, 2011, 07:47:25 pm »

Jeep UK are only offering model year 2012 Wranglers with diesel engines and auto boxes. I figured this made good sense, despite the 2.8 being long in tooth and the new Pentastar v6 petrol being a really nice unit. I mean, Jeeps use a lot of fuel, you get so much more mpg out of diesel, you'd be mad to buy a petrol Jeep right?

Wrangler Sahara 4 dr Auto 3.6 V6

Combined 24.1 mpg
Extra Urban 30.7 mpg
Urban 17 mpg
0-62 8.9 sec
top speed 112mph

Wrangler Sahara 4 dr Auto 2.8 CRD

Combined 34.0 mpg
Extra Urban 38.7 mpg
Urban 28.2 mpg
0-62 10.7 sec
top speed 107mph

Time for some maths!

So on the Sahara, ie like for like, the diesel gets 26% better mpg on the long extra urban run, a whopping 66% better fuel economy around town but overall 41% improvement in mpg in general.

Diesel is clearly the way forward, surely!?

The cheapest petrol near me is 128.9.
Assuming 1,000 miles per month on the combined cycle the Pentastar would cost:
1 month - £243.14
1 year - £2,917.68
3 years - £8,753.04
5 years - £14,588.40

The cheapest diesel near me is 136.9
Assuming 1,000 miles per month on the combined cycle the diesel would cost:
1 month - £183.04
1 year - £2,196.48
3 years - £6,589.44.
5 years - £10,982.40

So over 5 years and 60,000 miles I would save £3,606 by running the diesel.
I don't know what the difference in tax would do to that figure, I assuming the diesel is cheaper on tax but still in a high bracket but probably a good couple of hundred quid a year to save there.

I'm not sure what the price difference between the 2 engines is as I guess officially we only get the diesel over here which makes a fair comparison difficult...

But typically diesels cost a good £1,000 or even £1,500 more than petrol equivalents right? If so it looks like running a diesel saves you less than £3,000 over 5 years even allowing for the £300 per year tax saving...

Now, just for kicks imagine we LPG the Pentastar and lose 15% fuel economy in doing so...

The cheapest LPG near me is 70.9

1 month - £157.23
1 year - £1,886.76
3 years - £5,660.28
5 years - £9,433,80

This means that over 5 years the Pentastar on LPG becomes £1,500 cheaper to run than the diesel, or even £2,500 - £3,000 cheaper than the diesel if we assume the Pentastar is that much cheaper to buy as we have said.

But then we need to take £2,000 off that saving for the cost of the LPG conversion in the first place. So a Pentastar on LPG would be between £500 and £1,000 cheaper than a diesel over 5 years...

I may have to rethink my opinion on diesel being the only real engine option.

Even if you use the Jeep daily and do decent mileage over 5 years the savings don't really add up to that much (I know £2,500 is still £2,500) really?

And if LPGing the Pentastar is viable then it would be the cheapest total cost of ownership, and be faster and frankly much nicer to drive and less of a health hazard!

Did you ever think we were being conned into diesels?!?!

Fieldy · « **Reply #1 on:** November 18, 2011, 09:26:26 pm »

Lol.... Welcome back Andy

HardRockCamaro · « **Reply #2 on:** November 18, 2011, 09:51:01 pm »

You know me, I only work from numbers, not opinion!

In god we trust.
Everything else we measure...

FUBAR · « **Reply #3 on:** November 19, 2011, 01:30:21 am »

Basically what you're trying to say is that the Oil companies & government have carefully controlled the prices & Tax on everything so that in the long run we all get Ass-Fk'd for the same exhorbitant cost of daily travelling no matter what fuel type or option we chose.

The 'differences' you describe above are so small in the grand scheme of things that in the end it makes no difference really does it...

Therefore you may as well chose the more fun option.

Decision made... the V6 it is then

F Body · « **Reply #4 on:** November 19, 2011, 03:36:48 am »

Quoting: FUBAR

Therefore you may as well chose the more fun option.

Decision made... the V6 it is then

Decision made it's the V8 then

HardRockCamaro · « **Reply #5 on:** November 19, 2011, 07:01:36 am »

To be honest I assumed about a 40% improvement in mpg as diesel has a 40% higher energy value, but if the engine costs a £1,000 more due to the turbo, piping, stronger block and internals etc then that, combined with the higher cost of diesel, really eats into the savings so you have to ask yourself, is it really worth it? I had assumed that it wasn't until the 3 year mark, and then the savings would kick in a bit more and after 5 years I'd have made a decent saving.

But it looks like over 5 years and 60,000 miles diesel saves about 5p per mile.

For that I'd rather have the petrol engine which is quieter, nicer, more powerful etc etc?

And this is before we consider the health problems of diesel engines if we're feeling socially responsible...

The savings just aren;t there to fret over buying a diesel new or maybe even used...

The ore mileage you do and the longer you keep it the more you save, but the difference certainly isn't anything like as much as I thought...

F Body · « **Reply #6 on:** November 19, 2011, 07:57:40 am »

Pretty sure our next family car will be a petrol rather than the current diesel

The worst thing with the modern diesels is that they run so cold, in winter it takes our little 1.3 diesel nearly 10 miles of driving before it gets warm

Andy · « **Reply #7 on:** November 19, 2011, 09:35:17 am »

Quoting: F Body

The worst thing with the modern diesels is that they run so cold, in winter it takes our little 1.3 diesel nearly 10 miles of driving before it gets warm

Whats with that? Our company van doesn't get warm until we're at work, an 8 mile drive! i first reckoned it was a con with VW trying to sell you a winter package or something!

Incursus · « **Reply #8 on:** November 19, 2011, 09:55:29 am »

Mondeo warms up in less than 3 miles, not as quick as the stang but not bad.

F Body · « **Reply #9 on:** November 19, 2011, 10:58:48 am »

Quoting: Andy

Whats with that? Our company van doesn't get warm until we're at work, an 8 mile drive!

It's the same with all the modern common rail diesel engines I drive, IMHO it actually makes them dangerous to drive when the temperature gets really cold i.e below -10c

Last year I drove a new Astra over the North Yorkshire moors and the dashboard temperature gauge was showing -16c

We had to stop every two miles, then sit with the engine revving near the red line to get enough heat on the windscreen to stop it freezing on the inside

Compare that with my Z28 that blows warm air in 300 yards and is full temp hot and toasty in a mile and half ( although the oil pressure stills says the oil is cold )

Incursus · « **Reply #10 on:** November 19, 2011, 11:31:29 am »

HFS for the win

art b · « **Reply #11 on:** November 19, 2011, 11:51:58 am »

the difference between derv and petrol can be 6p a litre,
which can be nearly 50p a gallon... so unless your doing lots of miles the extra cost of a diesel car is a false economy ..

unless you have a cheap as a chips old oil burnin audi...mine has more than paid for its self over the last two years...

Cunning Plan · « **Reply #12 on:** November 19, 2011, 03:30:59 pm »

Quoting: FUBAR

Basically what you're trying to say is that the Oil companies & government have carefully controlled the prices & Tax on everything so that in the long run we all get Ass-Fk'd for the same exhorbitant cost of daily travelling no matter what fuel type or option we chose.

We drove across Europe this summer, through France, Belgium, Netherlands and Germany. Everywhere had Diesel on sale for 5 to 10 cents cheaper than Petrol. You get back to England and diesel is 4 to 10p more expensive. Yet, Diesel is a bi-product of Petrol - you can't get Petrol without creating Diesel.

So, does 20 miles of English channel really raise the cost by that much

Fub's is right, the previous goverments have worked out that Diesel cars genrally have a longer range than Petrol cars and do not need to fill-up as often, so to get the same amount of duty and vat from them, they pay a higher price to start with

HardRockCamaro · « **Reply #13 on:** November 19, 2011, 05:14:30 pm »

Diesels take longer to warm up as they are a thicker walled block.

art b · « **Reply #14 on:** November 19, 2011, 07:43:54 pm »

my dwesil audi takes its heater matrix pipes, directly to and from from the rear of the head,
so it heats up really quick...no probs with misted screen

it doesnt matter if the engine is coldish,

it does take around 20 mins to get up to temp tbh...

but it is a big 5 cyl 2.5l lump..

Quoting: F Body

It's the same with all the modern common rail diesel engines I drive, IMHO it actually makes them dangerous to drive when the temperature gets really cold i.e below -10c

but still better than that wobbly old push bike....

philoldsmobile · « **Reply #15 on:** November 20, 2011, 04:57:43 pm »

Diesel takes longer to warm up because its more efficient, I.e. more energy goes into propelling the car, and less is wasted as heat. Some bigger diesel people carriers actualy have diesel fired heaters rather than coolant fed ones.

There are some advanced petrol units now such as the multi air that can exceed diesel economy while giving more power and refinement.

HardRockCamaro · « **Reply #16 on:** November 20, 2011, 07:49:31 pm »

I don't see how diesel uses more of its energy to propel you forward when it works on the same principle, ie an explosion, which generates heat, forcing the piston down? You go further on a litre of diesel than a litre of petrol as diesel has a 40% higher calorific content, ie there's 40% higher energy stored in it.
The reason for taking so long to warm up is that "warming up" is a measure of coolant temperature and the thicker walls of a diesel block required to keep the higher compression force from blowing the thing apart, mean that heat takes longer to transfer through the block to the coolant.
In the same way thinner walled petrol engines warm up quicker than thicker walled petrol engines.

One thing I was looking into today funnily enough is radiator covers, or winter fronts s they are often known, seen on big rigs and London taxi's, a bit like sticking a bit of cardboard to shield most or all of the radiator. Aside from the theory that the radiator is oversized to allow good performance in slow traffic on a hot day and thus too much cooling is done on a cold day on the move, I can't see the point of them.... A couple of people have suggested the vehicle warms up quicker with one, but as the thermostat would keep the coolant in the block anyway until it reaches a certain temperature I fail to see how?

I've read a couple of theories but it seems to be all guesswork, I've not seen any hard proof of if it does anything and why...

Know anything about it?

Cunning Plan · « **Reply #17 on:** November 20, 2011, 08:13:27 pm »

Quoting: HardRockCamaro

funnily enough is radiator covers

I assumed they were used to limit the amount of 'wind-chill' making the coolant even colder when travelling and to aid warming up faster - much like Ice Road Truckers:

HardRockCamaro · « **Reply #18 on:** November 21, 2011, 07:56:06 am »

Yeah I notice they use them a lot

Do they stop the coolant from getting too cold before it re-enters the engine?
Is it supposed to help retain the heat in longer when you stop?
Does it actually warm up quicker?
Is it only of benefit to diesels?
Was it needed back in ye olde days and now not really but people keep doing it?

Enquiring minds would like to know...

art b · « **Reply #19 on:** November 21, 2011, 12:19:10 pm »

i think people used to block off the bottom part of the rad in cold weather,

which would allow it to cool the coolant, but not freeze the bottom part..maybe...

F Body · « **Reply #20 on:** November 21, 2011, 05:36:01 pm »

Quoting: art b

i think people used to block off the bottom part of the rad in cold weather,

Indeed I did with cardboard

I believe that some new cars such as the Ford Focus have a louvered grill which only opens when the water temperature gets hot

HardRockCamaro · « **Reply #21 on:** November 21, 2011, 06:17:03 pm »

For better aero...

The home or aftermarket mod I have only seen in winter so I'm assuming it's a temperature thing as opposed to aero.

Fro what I can gather it's to keep heat in which can help warm the engine up quicker, ensure it dens't lose heat as fast when stopped temporarily and the coolant is not cooled down as much when on the move so the coolant entering the engine isn't as cold thus maintaining a more consistent temperature and also meaning the engine is not over cooled so your heater works better.

I'm tempted to try it on the Jeep as it has the large open 7 slot grille, just to see what it does