I have started thinking about a possible future replacement for the Superb which I have had for over two years now, and wondered if anyone has any opinion or experience of my preferred choices. I have always liked multi (read 6) cylinder engines, particularly diesels, and I must say I have developed a bit of a bias towards an Audi A6, either a 2.7 tdi or a 3.0 tdi, ideally in Le Mans trim with a manual box though they are rare particularly the 3.0. Choice number two would be a BMW 530d SE spec, again a manual box. Not sure if I could live with the image though, and that interior, oh it's so much different than the Superb's.... don't particularly like it to be honest, but it's a great overall package. Oh, RWD winter troubles also not very inviting.... But all of these have dual mass flywheels, and BMWs in particular are also renowned for turbo issues, which considering the reliability from the 2.5 tdi lump I have been enjoying so far might not be a step in the right direction...

^{Used or new?}

^{If used, by far the best choice is to go for previous Audi A6 3.0 TDI quattro 6-spd manual, in at least 204bhp guise.}

^{Comparable interior space, more power, better handling, and bigger fuel tank, plus interior of comparable quality.}

^{If you want a new car, you are in trouble, I was considering replacing my Superb for the past 2 years (well, actually passing the Superb to my wife while I drive something new), but ever since Audi got rid of manual boxes on the A6 quattros, it's just not worth the money as I tend to keep my cars for 8+years / 150k+ miles. A4s/A5s are just too small.}

^{I would not buy BMW primarily because of RWD, why buy a car that is dangerous and sometimes next to useless for 2 (winter) months in a year.}

^{FWD or quattro is my choice. Image is another story.}

Used.

There are some nice 3.0 tdi manual quattros about, but I'm thinking is it really worth going for the 3 litre when the 2.7 isn't that far lower down on power, and it is noticeably more frugal, at least on paper. AT 100mph + might be a different story. Have not looked into gear ratios yet.

Yes, a diesel 530d with 500Nm through the rear wheels in the winter... ahem.... I think we are on the same page, FWD or 4WD is the way to do it.

Quattro obviously costs more in fuel and speed.

Do you know if either of these engines are B100 friendly? My 2.5 tdi is very happy on it, the VP44 is B100 "certified", but HPCR, ahem.... though there are people running S320cdi and 730d on them for many many miles without problems when having access to top quality fuel. Superb's fuel tank is pathetic in size, even with the tank vent mod, once the mileage "range" is zero, and I keep driving for a few more miles I can only push in 56 odd litres. And that gives me 460 miles at reasonable speed. My old Pug 605 could do 750 miles out of its 80 litre tank. So yes, tank size is a very important thing to me too. I think the 3.0 A6 comes with an 80 litre if I can trust google ;-) I was looking at 225PS versions.

Used.

There are some nice 3.0 tdi manual quattros about, but I'm thinking is it really worth going for the 3 litre when the 2.7 isn't that far lower down on power, and it is noticeably more frugal, at least on paper. AT 100mph + might be a different story. Have not looked into gear ratios yet.

Quattro obviously costs more in fuel and speed.

Do you know if either of these engines are B100 friendly? My 2.5 tdi is very happy on it, the VP44 is B100 "certified", but HPCR, ahem.... though there are people running S320cdi and 730d on them for many many miles without problems when having access to top quality fuel. Superb's fuel tank is pathetic in size, even with the tank vent mod, once the mileage "range" is zero, and I keep driving for a few more miles I can only push in 56 odd litres. And that gives me 460 miles at reasonable speed. My old Pug 605 could do 750 miles out of its 80 litre tank. So yes, tank size is a very important thing to me too. I think the 3.0 A6 comes with an 80 litre if I can trust google ;-) I was looking at 225PS versions.

Previous 3.0 A6 quattro comes with 80l tank, 2.7 come with 65l tank I think. All new A6 come with 65l stock, then you can optionally get 75l extended tank (and that tank extension is in fact fuel tank for parking heater, Audi only introduced it as separate factory option because half of customers left the showroom after hearing 65l fuel tank and 3.0l engine in one sentence )

I normally look at new cars to buy, so 2.7 FWD Audi is already way overpriced (better to buy the crazy 3.6V64x4 Superb Estate and you still have extra money left for fuel cost difference for next 10 years) .

The whole point of buying a new Audi (unless you want a badge only) is to get decent on-road quattro drive with matching engine power.

I agree that if you look at used cars getting the 2.7 might be sensible, especially if running costs matter.

I am curious about your Superb's fuel tank, is it an earlier one (pre-2006)? You are saying 56l after venting, but mine was 64l stock, and 69l after venting (still it was a shock that expansion space was only 5l, it was 9l on Mk1 Octavias). I checked the 69 l because I had tank open at some point, but I also filled up 68.3l on one occassion... scary drive.

B100 support is unlikely on CR engines, VW does not allow B100 ever since they had to fix 3000 PD engines under warranty after water coming out of biodiesel damaged PD units (one winter in Germany).

The 1.6CR diesel (with a Roomster attached to it) that I am getting for my wife has the following statement:

Your vehicle is not adapted for use of biofuel (RME), therefore this fuel must

not be refuelled and driven. The use of biofuel (RME) can lead to damage to the

engine or the fuel system.

However, considering that in most countries fuel is mandated to contain at least 7% - 10% biodiesel as it replaces more expensive lubricity and cetane boosters, chances are that all newer diesel engines can take biodiesel without dissolving seals, but probably do not tolerate increased water content. If I had access to biodiesel now, I would not use more than B50 in summer and only straight diesel in winter, on a CR engine. Also, I am not sure how DPF system reacts to biodiesel, on one hand it should be cleaned much better, on the other the separate fuel injector may only be calibrated for diesel viscosity. By comparison, on my 2.5TDI I also used B100 in summer and B50 in winter whenever I could fill it up (mostly driving across Germany).

Edited 11 April, 201214 yr by dieselV6

I'm with dieselV6 on the subject about venting. I too have 69L tank after venting was removed. My car will do 700 miles on one tank, almost every single time.

Edit: I'm driving in Germany frequently, like 2 times a month (long distances) and i'm always getting Shell V-Power diesel. I don't know what they put in it or if it is actually any different, but my engine likes it very much. On rolling road i'm getting 15 bhp extra, which makes a total of about 180 bhp. Torque is up by 10. The sound is also different for some reason and I get even better response from the throttle. Too bad that regulations makes it hard for Danish Shell to offer V-Power diesel.

Mine is indeed a pre-2006, it's a 2002 in fact. Perhaps the gauge calibration is off. I read in a Bosch document released for VP44 pump and pump systems (a bit generic, non-vehicle specific) in German, that there is a fuel cut-off at low fuel level to protect the pump from running dry. So theoretically I could test how far I could drive beyond the zero miles range point on the computer and then see how much I can put in it. Perhaps it's just a matter of gauge calibration. Before I vent modded, and just brimmed it as normal, the gauge would move off the max within 20 miles!! A bit unnerving. Now it's about 100-120 miles before fit moves off the 100% mark. But yes, as soon as I get to zero miles remaining, I can only put into it 54-56 litres. Last time I managed 58, but that was probably driving for another 20 miles after zero miles range reached. I was sweating by then, not healthy :-)

RME has higher lubricity that diesel, allegedly, especially the ULSD variety, which is the norm in W.Europe. Production methods of biodiesel vary greatly, as does the raw oil quality and origin. Water washing is a quick way of eliminating excess soaps and glycerol from the final product but unless then reheating the oil, which costs energy, to vaporise the water off, or storing it in a dry vented place for a month prior to use, the water content can be as high as 1-2%. When I produce my own biodiesel I use the dry wash method, as it is not only environmentally friendly, but in my experience produces RME of superior clean water-less quality that can be poured straight into the tank.

Common rail should technically be perfectly happy with pure RME. It's the variation of the quality and cleanliness of RME, in particular as DIESELV6 pointed out water content, but also excess soaps and methanol, which is the problem, not the RME itself. Pump bio unfortunately varies very much in what you get on a day to day basis too. I was worried about DPF too, the post injection targeted at raising the exhaust temperature up to the level required for DPF regeneration is calibrated for std diesel, and RME might have different characteristics. Worst case it will not achieve the target temperature and it will eventually go into limp home mode requiring dealer intervention. However, as RME contains around 11% oxygen, smoke generation is greatly reduced so the frequency of DPF regeneration is also reduced with associated fuel consumption benefits also.

As far as seals are concerned, all manufacturers except Ford have gone to Viton seals on all fuel systems components from mid-1980's onwards, so this is is not a problem. In winter the cloud point of biodiesel is an issue especially at high water content, but even perfectly dry, hence preferable to mix with normal winter diesel. I ran my car this winter on B100 at -7 deg C with no problems though, but any lower than that might require a change of chemistry.

Edited 11 April, 201214 yr by oh_superb

^{I seem to recall that early Superbs had 52l fuel tank, which would correspond well to 58l vented. But I might be wrong and your gauge is off.}

^{An easy way to address most biodiesel risks is to mix it with normal diesel, B50 won't have much different parameters than B0, similar viscosity, burn temperature, but higher cetane, much better lubricity and cleaner burn, not to mention the cleaning effect of the unburned soap .}

^{If you make your own fuel and are confident it is of good quality, then perhaps even B70 would be OK for long term use. Most biodiesel specific problems arise from B80-B100 use.}

^{Water in biodiesel can also be addressed by adding 1%-2% pure isopropanol (note must be isopropanol, not methanol nor ethanol, and of course 100% pure, so no more water is added), 1l-2l per 100l really is not much but will bind the water well. Good quality biodiesel has more lubricity and higher cetane anyway, so isopropanol won't hurt. It is similar trick as adding ethanol to petrol engines to bind and burn water.}

^{Water causes 3 main problems, corossion, momentary loss of lubricity and freezing out inside cold engine (that's what hurt the PDs). Isopropanol addresses all 3, as the water/isopropanol becomes fully miscible with biodiesel, and does not freeze out.}

^{Anyway, looks like we strayed off-topic a little}

We did stray off topic, but it's been a good exchange of knowledge. I did not know about the isopropanol trick but now I do... thanks.

I used long term settled oil so no water content, but unfortunately water is created as a by-product of the transesterification process but again long term settlement of biodiesel resolves this... unfortunately waiting and commercial profit do not exist in one sentence, but for a modest home brewer like me making a few hundreds of liters a year, it's not an issue. And it's good fun.

If I do get a 3.0 tdi in a year or two, I might run it on B50. I am sure it would tolerate that very well.

They still make a manual A6 Allroad 3.0 TDi with a manual gearbox. I've tested it and it's utterly wonderful. 40mpg too.

Out of interest, how would a PD 130 engine react to running on biodiesel?

Allroad has air suspension, not something you want to live with after a few years. Also, manual allroad has much shorter gearbox than previous normal a6 3.0 quattro , resulting in increased fuel consumption at speed, and lower top speed.

Plus I do not think orders accepted anymore as new Allroad A6 (automatic of course) was announced allready.

PD130 used to be B100 capable, but VW gave up on this as explained earlier. PDs did not like biodiesel in winter a lot.

I know the original Allroad was riddled with problems regarding the air suspension, but apparently the newer model hs better... for now.

Regarding the gearbox, can't remember the exact ratios but it cruised incredibly well. It wasn't that far off my PD130 regarding consumption, which illustrates how far diesel engines have come.

Shame regarding biodiesel. Fed up of the prices. Would running it on biodiesel in summer cause it to suffer?

The UK govt has kindly increased the tax on biodiesel at pumps (up 20p) which means that commercial biodiesel is no longer viable.

The only way is to buy your own processor do your research and make your own fuel. But guaranteeing top quality is another matter - requires experience.