XUD9 vs DW8 discussion

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: XUD9 vs DW8 discussion

Post by CitroJim »

I always pride myself on understanding diesel combustion fairly well and never understood how cetane improvers can make a significant difference to running at normal running temperatures...

My understanding has always been that the cetane rating of diesel fuel is essentially the opposite to that of octane rating for petrol in that it is a measure of a fuels' readiness to detonate at a given temperature and pressure. It is generally upped to a higher level in the winter to assist in cold staring and this generally is where I've understood a high cetane rating is beneficial - it improves cold starting.

Cetane ratings also influence the ignition delay... i.e. the delay from start of injection to actual detonation. This is longer in the cold than in the warm and is the reason why old-school diesels have cold ignition advance set on their pumps.

On a modern electronic diesel any changes in cetane should be compensated for automatically so no difference in performance should be seen.

Also, a diesel will burn any old hydrocarbon that can be ignited under heat and pressure so once hot what fuel it is any what cetane rating it has should in theory at least, be irrelevant.

Hence why a diesel can run on anything from coal dust to peanut butter. If the pump can pump it and inject it the engine will run and most see no significant performance difference between running DERV or cooking oil in an XUD...

Having said all that I know that many report the 'premium' diesels do indeed give benefits. I'm not disputing it but I've never seen any difference myself in XUDs or early HDis and I wonder how much is down to placebo effect and the fact these fuels may have good detergents in them and any performance improvement comes about from having a clean fuel system as a result of their use...

Your educated thoughts on this would be appreciated as I want to understand it properly... I have not yet seen a satisfactory answer to dispel my belief that it's mostly marketing hype.
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
Harlequin
Donor 2023
Posts: 912
Joined: 11 Jan 2006, 21:11
Location: Eastbourne , East Sussex
My Cars: Xantia Activa - one day I`ll own her again! Also miss my `old` 405 GLx4
2005 C5 3 Litre V6 Exclusive in Mauritius Blue and my 1997 Xantia Exclusive V6
x 23

Re: XUD9 vs DW8 discussion

Post by Harlequin »

Simon
User avatar
white exec
Moderating Team
Posts: 7445
Joined: 21 Dec 2015, 12:46
Location: Sayalonga, Malaga, Spain
My Cars: 1996 XM 2.5TD Exclusive hatch RHD
1992 BX19D Millesime hatch LHD
previously 1989 BX19RD, 1998 ZX 1.9D auto, 2001 Xantia 1.8i auto
and lots of Rovers before that: 1935 Ten, 1947 Sixteen, 1960 P5 3-litre, 1966 P6 2000, 1972 P6 2000TC, and 1975 P6B 3500S
x 1752

Re: XUD9 vs DW8 discussion

Post by white exec »

On both BX, XM and D4D, we've often had to put up with less than wonderful performance (i.e. lack of torque) after having to fill up in desperation with budget or supermarket fuel. All I can say is the difference in driveability can be marked.

I don't bother with posh diesel (super super premium advanced, or whatever, and higher priced), but just buy standard grade - usually Repsol, which is consistently good. Many friends here have found the same, with older and new cars running on an exclusive diet of supermarket/budget fuel encountering problems. Diesel workshops here advise against doing this, and suggest a combination of good-quality fuel and an Italian tune-up to get things working properly again.

I think it depends on the journey, and what terrain you encounter. Here in the mountains, being able to tackle steep corners and inclines is of daily importance, especially heavily loaded.

It really isn't just marketing hype. I agree with you, Jim, diesels will run on almost anything, it's just a matter of how well they run though.
Last edited by white exec on 29 May 2017, 00:39, edited 1 time in total.
Chris
User avatar
van ordinaire
(Donor 2017)
Posts: 2537
Joined: 23 Jun 2015, 14:45
Location: Live & work in London but weekend in Devon (or do I now live in Torbay & work in London?)
My Cars: Citroens:-
'81 2CV Club (quietly sleeping in a parallel universe)
'05 (yes, really) C15
'97 Xantia Exclusive estate
others:-
'96 Jeep Cherokee Limited - the "donor"
'99 Jeep Cherokee Orvis - the green one
'97 Jeep Cherokee Limited - the red one
'99 Cadillac Seville STS
'96 Cadillac Eldorado ETC
& numerous what might be described as abandoned projects!
x 405

Re: XUD9 vs DW8 discussion

Post by van ordinaire »

As some of you will know, my sudden interest in additives arose because of a particular issue, but, having caught up, a few random though, hopefully, relevant thoughts:

My old van does seem to run better when there's veggy (usually sunflower oil) in there, even if it's only 5 litres to a tank: placebo or lubricity?

What's the difference between a diesel & a multifuel engine (apart from the fact the latter will run on petrol)?

DERV - now there's a dear old fashioned term; how/why isn't it diesel?

What exactly was "bunkering service" - & why don't we need it any more?

Is it really being suggested that we use a supermarket's own brand additive to cure the deficiencies of their fuel? The irony is delicious (& probably smells better than the additive).

Do I correctly understand that one particular Wynn's product was chosen over the other two for its smell - or was it simply because that was the only one that was available locally?

Why is (a lot of) Eurodiesel blue?
Citroens:-
'81 2CV Club :cry:
'05 C15 :!:
'97 Xantia Exclusive estate [-o<
others:-
Jeep XJ Cherokees x 3 :?
'96 Cadillac Eldorado
'99 Cadillac STS :|
& the numerous "abandoned projects" #-o
User avatar
white exec
Moderating Team
Posts: 7445
Joined: 21 Dec 2015, 12:46
Location: Sayalonga, Malaga, Spain
My Cars: 1996 XM 2.5TD Exclusive hatch RHD
1992 BX19D Millesime hatch LHD
previously 1989 BX19RD, 1998 ZX 1.9D auto, 2001 Xantia 1.8i auto
and lots of Rovers before that: 1935 Ten, 1947 Sixteen, 1960 P5 3-litre, 1966 P6 2000, 1972 P6 2000TC, and 1975 P6B 3500S
x 1752

Re: XUD9 vs DW8 discussion

Post by white exec »

The three I mentioned (Wynns, Millers and 3CV) all look and smell the same, and have almost identical MSDS sheet ingredients. The choice was down to local availability - currently 3CV.
Chris
elma
Posts: 3745
Joined: 13 May 2007, 02:17
Location: United Kingdom
My Cars: Undisclosed
x 287

Re: XUD9 vs DW8 discussion

Post by elma »

I always found xuds smoothest on BP or shell diesel, best economy too. I saw no improvement from super diesel either, but wouldn't expect to.
My v6 is similar but happily drinks at Texaco as well, high octane only. Filled with regular unleaded it loses torque and smoothness. Fill with Esso, supermarket or other budget fuel and it barely runs or sometimes refuses altogether (asda fuel caused that and I thought I'd broke it)
Online
User avatar
myglaren
Forum Admin Team
Posts: 25362
Joined: 02 Mar 2008, 13:30
Location: Washington
My Cars: Mazda 6
Ooops.
Previously:
2009 Honda Civic :(
C5, C5, Xantia, BX, GS, Visa.
R4, R11TXE, R14, R30TX
x 4888

Re: XUD9 vs DW8 discussion

Post by myglaren »

Mine seems better on Torq standard diesel than anything else, including 'super-premium' diesel including Torq's own.
Been adding Redex for six months now and no difference whatsoever.

It did do very well on Bio though, n longer available.
User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: XUD9 vs DW8 discussion

Post by CitroJim »

None of my cars seem to care a jot what fuel they have...

My Activa might be a tad more frugal on premium but that's all and fully expected given it's injection is adaptive to different octane ratings... To me the difference is hardly noticeable...

The Pug of Love and Gabriel are not fussy at all..

Must be how I drive...

Now, my bike engine is totally different and that has very critical and specific fuelling requirements ;)
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
Hell Razor5543
Donor 2023
Posts: 13726
Joined: 01 Apr 2012, 09:47
Location: Reading
My Cars: C5 Mk2 VTX+ estate.
x 2993

Re: XUD9 vs DW8 discussion

Post by Hell Razor5543 »

Burger and Chips? :D
James
ex BX 1.9
ex Xantia 2.0HDi SX
ex Xantia 2.0HDi LX
Ex C5 2.0HDi VTR
Ex C5 2.0HDi VTR

C5 2.2HDi VTX+
Yes, I am paranoid, but am I paranoid ENOUGH?
Out amongst the stars, looking for a world of my own!
User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: XUD9 vs DW8 discussion

Post by CitroJim »

Hell Razor5543 wrote:Burger and Chips? :D


No!!!! That’s akin to putting used veg oil straight into an HDi :lol:
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
Hell Razor5543
Donor 2023
Posts: 13726
Joined: 01 Apr 2012, 09:47
Location: Reading
My Cars: C5 Mk2 VTX+ estate.
x 2993

Re: XUD9 vs DW8 discussion

Post by Hell Razor5543 »

Ah, but the bun was some of your own home baked bread! Surely that makes a difference?
James
ex BX 1.9
ex Xantia 2.0HDi SX
ex Xantia 2.0HDi LX
Ex C5 2.0HDi VTR
Ex C5 2.0HDi VTR

C5 2.2HDi VTX+
Yes, I am paranoid, but am I paranoid ENOUGH?
Out amongst the stars, looking for a world of my own!
User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: XUD9 vs DW8 discussion

Post by CitroJim »

Hell Razor5543 wrote:Ah, but the bun was some of your own home baked bread! Surely that makes a difference?


Yes, a big difference :D I'm a vegetarian so as long as the burger is either bean or fish ;)

I don't eat processed meat of any sort...
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
ekjdm14
(Donor 2020)
Posts: 1810
Joined: 19 Jan 2015, 17:42
Location: Congleton
Lexia Available: Yes
My Cars: '95 Xantia 1.9D automatic - 109k one of two remaining
'03 206 GTi180 - 97k in pieces being brought back up to snuff
'03 206 1.9TD - home-built veg-fuelled B-road bruiser
'99 306 SE 2.0i cabriolet - 92k awaiting service work ready for next summer
'97 306 XS 1.6i 3 door, Bianca White, from dead 12 years & seized solid to road legal in 7 days
x 212

Re: XUD9 vs DW8 discussion

Post by ekjdm14 »

van ordinaire wrote:DERV - now there's a dear old fashioned term; how/why isn't it diesel?


DERV is simply an acronym for Diesel Engined Road Vehicle as I understand it...
'95 Xantia LX 1.9D-auto, Black, 109k
'03 206 GTi180 94k in surgery
'03 206 1.1S XUD9TE/veg project :mrgreen:
'99 306 2.0SE cabriolet 95k summer toy
'97 306 XS 1.6i 99k sat 12 years, fixed in 7 days, 150mile maiden voyage :rofl2:
elma
Posts: 3745
Joined: 13 May 2007, 02:17
Location: United Kingdom
My Cars: Undisclosed
x 287

Re: XUD9 vs DW8 discussion

Post by elma »

That's right but many will say it's diesel oil for road vehicles. The e clearly standing for oil for. Apparently it's a ww2 army acronym and they meant diesel engined...
User avatar
van ordinaire
(Donor 2017)
Posts: 2537
Joined: 23 Jun 2015, 14:45
Location: Live & work in London but weekend in Devon (or do I now live in Torbay & work in London?)
My Cars: Citroens:-
'81 2CV Club (quietly sleeping in a parallel universe)
'05 (yes, really) C15
'97 Xantia Exclusive estate
others:-
'96 Jeep Cherokee Limited - the "donor"
'99 Jeep Cherokee Orvis - the green one
'97 Jeep Cherokee Limited - the red one
'99 Cadillac Seville STS
'96 Cadillac Eldorado ETC
& numerous what might be described as abandoned projects!
x 405

Re: XUD9 vs DW8 discussion

Post by van ordinaire »

elma wrote: . . . Apparently it's a ww2 army acronym and they meant diesel engined...
A lot of miitary slang found its way into common use, prang, gremlin &, of course, jeep being more obvious examples BUT how/why did "DERV" come to appear on the globes on forecourt pumps - & what did it replace?

Oh, & why did the army have an acronym for something they didn't have for another 50 years?
Citroens:-
'81 2CV Club :cry:
'05 C15 :!:
'97 Xantia Exclusive estate [-o<
others:-
Jeep XJ Cherokees x 3 :?
'96 Cadillac Eldorado
'99 Cadillac STS :|
& the numerous "abandoned projects" #-o
Post Reply