Citroen XM Forum

My 2.1 td didn't have a problem with hills and there are plenty around here in yorkshire.

Norman

Give it a good run up and it's fine Norman, get stuck behind someone in a Toyota....

And give that supermarket diesel a miss

White Exec wrote:And give that supermarket diesel a miss

Do you have any evidence to support that claim. I have covered probably over 1 Million miles on all brands of fuel and other than finding lower mpg on Shell V-Power, have never noticed any difference on any other brand.

The calorific value is the same on all brands.

Dieselman wrote:

White Exec wrote:And give that supermarket diesel a miss

Do you have any evidence to support that claim. I have covered probably over 1 Million miles on all brands of fuel and other than finding lower mpg on Shell V-Power, have never noticed any difference on any other brand.
The calorific value is the same on all brands.

Experience aplenty, over hundreds of thousands of business (about 30k p.a. for 10 diesel years) and private miles all over Europe.
Became aware of the difference between diesel fuels long ago, whilst driving BX19RD, ZX 1.9D, and more recently XM 2.5, RAV4 2.0 D4D, and numerous hire cars, including Kia, Ford, LR, and Fiat.

Significant difference between diesel fuels is their cetane rating, not how much heat they produce. Look it up, and you will find that the cetane value of a fuel is related to the number and amount of additives put into the basic fuel. These additives are not cheap, and budget and supermarket fuels use less of them. Forgetting "premium priced" fuels, the better brands of standard diesel (eg Esso, Repsol...) simply produce more torque, particularly at low revs, and make hill climbing, towing, and out-and-out acceleration, noticeably easier, with less need to drop a gear on steep inclines.

Many diesel motorists pay the price of running on cheap diesel fuel, not only with reduced torque and slightly worse mpg, but also with increased engine and exhaust deposits, which, if not purged, can result in test failure.

I am really surprised by your comment, which doesn't reflect the experience of those working regularly with diesel engine performance and maintenance.

Petrol engines are another matter.

I have noticed a tiny difference between supermarket and say Esso fuel. Esso being a little quicker. But, apparently Tesco sell Esso fuels now, although not advertised as such. But essentially the difference is so small it doesn't make a huge difference really that I can tell.

How interesting. I've never noticed any difference between supermarket versus branded diesel personally and I'm sufficiently anal to work out my mpg every tank. I've never bought any of the 'super' fuels mind.

The cetane improving (and other) additives are, apparently, added at the diesel fuel distribution depot where the delivery tankers are filled - and it this operation which differentiates one 'brand' and type from another. Tankers from numerous fuel 'brand' companies fill their tankers at the same depots.

The larger depots themselves are - like major airports and Defence establishments - linked into a "national grid for fuel", operated on behalf of the government by a semi-privatised company. See https://en.wikipedia.org/wiki/CLH_Pipeline_System for details.

At an airport connected to the grid, airline operators have their planes refuelled (by contracted pumpers) from tap-off points at each apron. Individual airlines have fuel contract arrangements with individual oil companies (BP, Shell...) but they all draw the same fuel from the same pipe network. Who bills whom is simply a matter of subsequent accountancy; the fuel is all the same. The various oil companies' refineries simply pump their products into the same fuel grid, where, of course, it all mixes.

The major tanker refuelling depots need to be supplied, and, like airports, this isn't done by road tanker! It's a pipeline job (for logistical, security and safety reasons), and the individual oil companies do not, generally, have individual pipelines.

Tesco might well buy its fuel from Esso this month, but the supermarkets exert downward pressure on their buying-in price by shopping around, and so fuel type will not be consistent. In turn, the oil companies and wholesalers trim the price by economising on fuel additives, and one of the casualties of this process is a reduced level of additives (cetane improvers, lubricants, cleaning agents, anti-corrosion, biocides...) in supermarket- and budget-branded diesel road fuel.

Plenty on the web about this:
https://en.wikipedia.org/wiki/Cetane_number
https://en.wikipedia.org/wiki/Cetane_Improver
http://www.millersoils.co.uk/automotive ... sector=Car
-see also the MSDS sheet for what's in it

The differences in "pulling power" will vary from one car to another, and for some vehicles/drivers the differences may not be noticeable. From personal experience, though, all the diesels I've driven run better on good rather than budget fuel. Benefits include better starting, quieter running (down to the action of the combustion-modifying cetane improvers), smoother and better power delivery, and better fuel consumption.

Cheap fuel can often 'pepped-up' by the addition of a good diesel fuel supplement like Millers or Wynn's, to provide what is there by default on best brands. Trouble is, you have to add it, and some of the cost-saving disappears.

I have tried premium-grade ("posh") diesel from several companies, and cannot detect any difference whatsoever between these and their regular stuff. I think it's a marketing opportunity, which most cars don't need, but some drivers think is a good idea.

In The Xm i never noticed any difference between supermarket fuel and premium everthing stayed the same But in the c6 the difference is very noticable much better mpg and smoother engine response,

norman

In all my diesel cars I've never noticed any difference, other than as already mentioned, Shell V-power consistenly giving less mpg.

The calorific value is what governs the power output, the Cetane rating is the ignition enhancer to give quieter and smoother running. Cetane rating may give a marginal power improvement, but it is minor compared tot eh calorific value.

I logged all my fuel useage for many years and could clearly see a reduction in mpg in cold weather and when switching to winter diesel, but most particularly when running on Bio-diesel, due to it's lower calorific vlue.