Thread: What Diesel?

I know it's been discussed before, but couldn't find any recent threads...

...anyway, with fuel co's constantly tempting us with 'new and improved' juice at the pumps thought it might be worthwhile seeing what people are currently putting in their motors and whether it really makes any difference......

Never found any difference whatsoever with the premium brands.

With petrol there's a real, definable difference in that they have a higher octane rating. Engines which can alter their timing to suit will thus benefit from this. With diesel you can't just rase the octane so they resort to all sorts of daft additives and claim it helps. IMO, whilst the premium petrols can benefit some cars, the diesels are just marketing guff trying to leverage the press of the petrols such as Optimax.

From what I recall (and this is going back a good few years to A-level chemistry) raising the octane rating of diesel would actually decrease the performance of the fuel in an engine, as higher octane fuels are less likely to ignite under compression (in the absence of a spark, natch). This is obviously an undesirable quality in a diesel fuel.

So what you really want is a lower octane diesel fuel as this combusts more easily. However, too low and your engine doesn't reach maximum compression before the fuel ignites, so power and efficiency decreases.

I think that because of this, octane isn't used in relation to diesel fuels (people never seem to like the idea that the lower the number, the better, so it doesn't make for good marketing). Instead there's something called "cetane rating" which is some kind of measure of diesel fuel's quality (I'm struggling here). I seem to recall that the cetane number is mainly used to check the fuel meets regulations (that BS EN 5-something-or-other it says on the pumps).

Science aside, I agree with Vertigo1: you might as well be running your car on snake oil

No difference,whatsoever.
I just go to whichever diesel pump is free.
Fancy diesel is like fancy dog food.
Just makes the owners feel better,that's all.

Yup. No real difference.

I tried the "performance" diesel (ahem!) and it made no difference to normal. I try and buy the cheapest round the doors (try www.petrolprices.com to find the cheapest where you live) and then give the car a good horsing once or twice a week to clear the muck from the tail pipes.

Anyone else tried bio-diesel ?
I tried some from a local outlet.
It was only something like a 5-10% mix.
Again,no difference to running.

Ok this realtes to petrol but I'm sure part of it is relevant to diesel!

Evo and various other mags have done lots of research/tests on this in the last 6 months or so and the conclusion was always the same. If you have a very highly tuned car it was worth using the optimax type fules if you wanted a small gain.

what they did say was fuel goes off, stale if you like. The best thign you can do is use a busy petrol station as the fuel will be fresher.

I just sainsbury's fuel as it seems to suit my car better, smoother running and better miles to the tank, but this could just be in my mind of course...

Originally Posted by marriedblonde

what they did say was fuel goes off, stale if you like. The best thign you can do is use a busy petrol station as the fuel will be fresher.

You'll probably find that some of the additives they use to raise the octane (used to be benzine but not sure nowadays as this is carcinogenic) evaporate slowly over time, lowering the octane.

When I had the Sportback, I couldn't tell any difference between standard tractor oil and the expensive BP Ultimate stuff.

That said, I've not been able to notice any difference between standard and super UL with the 2.0T either. It goes very well with both types of petrol.

Originally Posted by bowfer

Anyone else tried bio-diesel ?
I tried some from a local outlet.
It was only something like a 5-10% mix.
Again,no difference to running.

Yes, I've used it in my Pug 306 HDi before, which I think was about the same mix as that. I thought things ran a bit smoother with it, but how much of that was a placebo effect I don't know (i.e.: if I didn't know it had biodiesel in, would I have noticed a difference? Probably not, in all honesty.)

My main reason for trying it was to show my support for biofuels. I've heard storied that on the continent all diesel is 5% biodiesel unless otherwise stated; why isn't it like that over here? With diesel cars becoming ever more popular every little step to easing the demand for derv is no bad thing, especially if it helps the price go down (diesel is 6p more expensive than petrol near me now )

I've tried to show my support for bio-diesel too.
Unfortunately,it's dearer and the only garage that sells it is miles away in the wrong direction,so it defeats the 'green' purpose !
If I had my way,the whole fleet (including the vans) would run on bio-diesel,but both MD's are dinosaurs.
One of them runs a 3.2TT and the other runs a 3.0 V6 Jag,so neither really give a fig about economy or the environment !

The manual for my car says if you have a DPF you can't use bioderv!

Resurrecting this thread.

Tesco Diesel is 5% bio, and as PJLarge says the 170TDI manual clearly states pure bio is bad news for 'no maintenance' DPF due to deposits and could need to be replaced if used. Might even mention the injectors too.

So is 5% doing just a little bit a damage every day, possibly causing future replacement situation - typically just as the warranty run out

Anybody worried or am I paranoid?

Can't see a 5% mix doing much harm,can you ?
Depends how many miles Audi reckon 100% bio would take to cause damage,then double it for 5% stuff !

Doesn't seem very forward thinking of Audi to equip their cars with parts that can't cope with green diesel.
They'll bleat on about recyclable parts in their brochure,for example,but take away the bio diesel option !

If you wording is accurate though,take note of the word "could"...
Big word that.
Big 'cover our corporate arse' word.

From the manual (just fetched it from the car)

"Caution: The vehicle is not designed for the use of biodiesel (FAME Fuel). The fuel system would be damaged if you use biodiesel."

"Caution: Vehicles with diesel particulate filter must not be driven with RMA fuel (biodiesel), as this could cause damage to the fuel system"

However if 5% bio still complies with EN590 then maybe that would be ok? I think I'll google for more info on EN590

EN590 (actually EN590:2000) describes the physical properties that all diesel fuel must meet if it is to be sold in the EU, Czech Republic, Iceland, Norway or Switzerland. It allows the blending of up to 5% Biodiesel with 'normal' DERV - a 95/5 mix. In some countries such as France, all diesel sold routinely contains this 95/5 mix.

from http://www.biodieselfillingstations.co.uk/approvals.htm

So I guess I'm just paranoid...

So how do you know what fuels contain some biodiesel? Is it just Tesco or do others do it too?

I heard tesco do it for petrol (bioethanol - that's how they get 99RON rather than 98) and for diesel as a tax break...
Looking around the web looks like it's probably quite common practice at least in Europe. And give Tesco don't exactly make their own fuel I'm guessing somebody else will be doing the same.

Here's a massive thread on DPF's and biodiesel

http://www.biofuelsforum.com/general...lters_dpf.html

Which I think, after a brief read, says that it shouldn't be a problem for % were talking here. And actually may be beneficial - so bowfer's comment about arse covering may be more accurate...

What made me paranoid is that my glow plug relay 'failed' straight after filling up from Tesco and that particular failure is highlighted by the emmission control system warning light...

Southpaw,

I've been running mine on and off on either Tesco or Shell, depending on whether I run out near home or work. I must admit I didn't even realise the Tesco stuff was a blend but it doesn't seem to have done any harm, nor does it seem to make any difference to either MPG or performance.

My glow plug relay has failed as well - I'm still waiting for replacement parts. Has yours been sorted?

No still waiting for Glow plug relay. Apparantly they've changed suppliers entirely and it's a different design, there are none in the country. Don't hold your breath for any this year...
I imagine there have been some quite heated discussions between Audi and the original supplier about the failure.

Oh I'm not the slightest bit worried that a 5% bio content would harm the fuel system or DPF as, if there was the slightest chance, Audi would be making sure everyone knew about it.

I was just curious really.