Technical guides Diesel & Petrol

[dieselV6]

First of all, apologies to other forum users as it's about to get more technical than is required again. We have tried to steer the thread towards more tidbits that are different in Mk2 (such as foot rests), but it appears for some forum users the most important thing is to discredit valid range concerns using smoke and mirror tactics.

Kiwibacon, you have repeatedly shown ignorance when it comes to max efficiency engine operating point and boost pressure behaviour. You claimed earlier boost does not change where it changes almost linearly with engine load (at 50%+ loads), and so will be 30%+ lower for 3.0CR running at same load as 2.0CR. Boost pressure does change with load for CR engines simply because pumping surplus air wastes power and increases NOx emissions.

Basically, you are trying to prove some point but even your own graphs and most other engine maps are against you. Cars are not designed for peak effciency at full load and max rpm at the same time, simply because it would lead to oversized exhausts and catalysts/particulate filters and that would cost more money. Beancounters do not like that.

The Superb Mk2 with 2.0CR 170bhp diesel does not have enough power, I refer you to Skoda brochure for maximum speed of 138mph. Mk1 2.5TDI speed was 139mph stock and that was not enough, it is now around 149mph. I do not want to buy yet another car that I need to remap from day one.

The Octy Mk3 184bhp diesel will have enough power and I already stated that. On account that Octy3 is lighter and presents less air drag than Mk2 Superb, even 150bhp diesel is good for 135mph already, and the vRS 184bhp 2.0CR is likely to do 144mph top speed.

Regarding fuel tank range, Octy 3 (with 50l tank) range will not be sufficient for 2hr+ autobahn travel even if 2.0CR 184bhp TDI used 17% less fuel than 2.5TDIV6 at 138mph (which I doubt, but for the sake of argument let's consider it).

Looking at ETKA diagram of Mk3 Octy fuel tank, I am almost certain it will not be possible to vent it as the valve assembly is not shown anymore. Ventectomy is no longer an option it seems. Look at the 2 diagrams:

Superb's fuel tank detail (ventectomy possible, look at the valve assembly, marked with an arrow). Similar arrangement was used at Mk1 Octy, Mk1 Superb and current Roomster. Removing the check valve (only on a diesel, never do it on a petrol!) gives 6l to 9l extra fuel tank capacity, on top of brochure listed values.

Mk3 Octy fuel tank detail (no check valve assembly, probably internal)

So it's 50l only - 8l reserve = 42l of fuel planned use. Even assuming 28mpg imp. or 10l/100km at 222km/h (which again I doubt), this gives 420km covered in 1h 53min at constant speed. And that's assuming 10l/100km or 28mpg at 222km/h or 138mph, I really wish the new engines used that little fuel at speed . Even looking at average speed, so assuming there's always roadworks on the way, Octy 3 fuel tank will last for 2h 5min before next visit to petrol station. Mk1 Superb can do 2h17min constant and 2h30min average at these speeds, still leaving ~20min reserve, and that's at 12l/100km or 23.5-24mpg.

Regarding spare wheel, I refer you to Skoda UK listings that specify tyre inflation kit as standard and space saver spare as an option. No mention of full sized spare. It's not the first time. Now we have option codes for full size spare and a picture to prove it it's there. Information that you have a choice and a picture you would not be able to get by going to a UK Skoda dealership for an Octavia 3 test drive. Not everyone lives in New Zealand.

Finally, regarding other poster's suggestions, The Touareg/Q5/Q7 do have big fuel tanks but use tons of fuel at high speed due to their shape/air drag The cars with 3.0CR engine in VAG group that are suitable for long range 130mph+ blasts are A4,A5,A6,A7,A8 and Phaeton, all without underbody protection, all with auto boxes only in quattro versions, some with air suspension, LWB Phaeton being the best value for money and best comfort choice at present, thanks to VW's £7k off offer in the UK. All thieves magnets in some countries in Europe. So you can see why I want to stay with Skoda. Also, if you compare any A6 eg vs A6 Allroad, you will find that gearbox is a good 6%-10% shorter on the Allroad. This is to cover supposed all terrain use, but means more fuel, less comfort and more noise at speed, not to mention even more inflated price.

Please discuss, preferably without resorting to complete denial of basic maths and real life

Edited 20 January, 2013 by dieselV6

[Dr Zoidberg]

You think 50 litres is a thimble.

How is that not a complete denial of basic Maths and real life?

[dieselV6]

How come the fuel tank is smaller than the Octy 2? 50 vs 55 litres. 11 gallons seems a bit small for the size of the car.

I would have liked however, to have had a larger tank in the new car.

50l seriously? Is the scout going to have the same thimble of a fuel tank, because that's going to be seriously poor.

So it is not just my concern. Plus I backed my complaint about small fuel tank with real numbers. You just enjoy winding people up.

[Llanigraham]

You just enjoy winding people up.

And you don't?

[dieselV6]

No, I provide information on as is basis, for other people to consider and use in their car planning/purchase. In fact, most technical information on Octy 3 in this thread following Colin's original (and very useful) post came from me.

Edited 20 January, 2013 by dieselV6

[Kiwibacon]

Some misconceptions here about NOx formation.

It is highly temperature dependent and the more boost you pump in, the lower the in-cyl temps and the lower the NOx production. Which is exactly why I said the 3.0tdi will not run the same boost schedule as a 2.5tdi which was designed for a less rigorous emissions regime.

But you've got it backwards, you think more boost = more NOx. But it doesn't.

This is the whole can't apply 2.5tdi data to a 3.0tdi thing. Likewise applying 1.9tdi data to a CR2.0 will lead you to some bizarre conclusions. Perhaps it already has.

I'm sure even Hasselhoff (when he's in Germany selling his music) doesn't need a car that can cruise at 140mph and cover 500km between fills at that speed. It's quite fantastical criteria you have for buying a car.

You *had* to remap the last one, why so scared about remapping the next?

Regarding the full-size spare. I think you missed the point of a full-size spare being possibly the most easy to fit accessory you can buy for a car. Open boot, remove whatever sits in the well, drop in full-size spare, secure full-size spare and shut boot.

Done.

Not really worth cutting a car off a list for.

[dieselV6]

Injecting less fuel while keeping boost pressure constant wil result in higher burn temperature and more NOx. More air with same fuel amount = more NOx, that is exactly why boost pressure goes down when load (and fuelling) goes down. That is also why EGR is injected at low engine loads, because in a throttle-less engine you cannot lower pressure below ambient and air/fuel ratio would be too rich, resulting in higher NOx.

I am sure most people travelling any significant distances across Germany will disagree with you, as you can get from most places to most places there by a largely derestricted autobahn, and at night I have at least 3 motorways where I can do 2hrs+ non stop at full speed, whatever the full speed of the car is. The best known is A2, 3 lane "airstrip" most of the way, look it up, I often travel it Junction 1 to Junction 80, that's 550km+, and it goes into A10, also largely derestricted on the southern part. Germany has almost 8000 miles or 13000km motorways, not sure if you are aware of that.

I often travel 1500km+ at a go in total, at night, and do not want to waste time at extra petrol stations, which are quite overpriced in Germany by the way.

I would not want to remap the next engine because 1.9s had a considerable number of stress related head gasket failures towards end of their life. I buy cars to keep them for 10+ years, stock power rarely causes any trouble throughout car's life.

Regarding "just chucking in the spare into boot", I am sure that is exactly why car manufacturers consider flat boot floor a good selling point, especially in estate cars. No thanks, I'd rather get a car with spare under floor. Which I can with Octy 3 despite SUK pretending it is impossible.

I am not cutting Octavia 3, in fact now that I found 184bhp diesel is in the works and full size spare is a go, Octy 3 is my preferred replacement for Mk1 Superb unless test drive shows up some other issue, e.g. legroom, or unless Mk2 Superb gets the 184bhp engine power upgrade.

Please do note that when this thread was started, from the UK it looked that I would have to put up with small fuel tank, no full sized spare and not enough engine power.

I would stop considering the car based on all 3 faults, it is now down to 1 fault - the fuel tank capacity and I'll work around it.

Edited 20 January, 2013 by dieselV6

[Kiwibacon]

You are confusing diesel with petrol. Leaner (higher a/f ratio) on a diesel is cooler.

I have a full-size spare in my 2.0tdi scout. Floor is flat and lowest of the two options.

[dieselV6]

No turbocharged engine at least in VW cars is keeping full boost pressure at reduced load, they all lower it to lower pumping loss. Or it lowers itself because turbocharger cannot supply enough pressure.

You are in NZ, I am in the UK, we initially only had access to UK data on spare. Yeti was the last car with space saver nonsense, you need raised floor to put full size in, so until the full size spare was confirmed, it was not guaranteed. As I said earlier, not everyone lives in NZ.

[Kiwibacon]

Yeti =/= Octavia. The spare tyre well and boot setup is quite different.

The 2.0CR's run more boost, more often than the 2.0PD. Peak boost is the same on the two, but the CR runs full boost a lot more and at lower throttle settings.

As I said, emissions regimes have changed the boost requirements and you cannot use data from older engines to predict the newer. Especially if you don't understand such basic operation as temperature vs fuel loading.

[dieselV6]

Reading with comprehension must be difficult. SUK downgraded Yeti to space saver only. Looks the same with Octavia 3 from already published data.

Bottom line is, you somehow magically skipped around the fact that I showed you clearly that even with magical fuel savings from 2.0CR, 50l fuel tank is inadequate for serious driving.

[chrisw880]

I would not want to remap the next engine because 1.9s had a considerable number of stress related head gasket failures towards end of their life. I buy cars to keep them for 10+ years, stock power rarely causes any trouble throughout car's life.

The 1.9TDI's are strong engines, and to my knowledge rarely suffer from head gasket failure. It's usually the turbo that lets go first on these engines

My Fabia PD100 is on 170k miles and it was remapped to 150bhp at 140k miles with no issues (apart from a turbo rebuild at 148k)

[FUBAR]

The 1.9TDI's are strong engines, and to my knowledge rarely suffer from head gasket failure. It's usually the turbo that lets go first on these engines

My Fabia PD100 is on 170k miles and it was remapped to 150bhp at 140k miles with no issues (apart from a turbo rebuild at 148k)

This 1.9TDi has hit 920000 km 6 months ago and still on original turbo! Don't know if he has remapped it.

[dieselV6]

1.9s are strong engines indeed, I wish they were still made. But you can get long term head gasket failure quite easily through overheating. For example through bodged timing belt.water pump job and not refilling the engine head properly afterwards. This is what happened to my Mk1 Octy at a dealership. Initially you notice slow coolant loss as it is expelled only under full load by exhaust gases leaking under the gasket, then after a while a full leak develops and a new head gasket please.

Similarly, on remapped engines long term operation around full power would overheat/overstress the gasket. We are talking 130mph almost constant speed 2hr+ runs here.

[FUBAR]

1.9s are strong engines indeed, I wish they were still made. But you can get long term head gasket failure quite easily through overheating. For example through bodged timing belt.water pump job and not refilling the engine head properly afterwards. This is what happened to my Mk1 Octy at a dealership. Initially you notice slow coolant loss as it is expelled only under full load by exhaust gases leaking under the gasket, then after a while a full leak develops and a new head gasket please.

Similarly, on remapped engines long term operation around full power would overheat/overstress the gasket. We are talking 130mph almost constant speed 2hr+ runs here.

I miss my 1.9 TDi :( Would you not say the same of any engine though if timing belt and water pump was messed up in the same way yours was? Where do you get to sit at 130+ for over 2 hours? Must do some speeding lol

[dieselV6]

German Autobahn, I travel a lot across Europe, usually overnight, see earlier posts for details. It's often closer to 3.5hrs at a time at 138mph, plus roadworks,some local speed limits and a short refuel stop.

The overheating gaskets I know about from the guy who chipped my Octy and Superb, it is a long term effect, hard to make it happen with UK speed limits even over 10 years. More 'popular' problem again in Germany where it is possible to load the engine to the max for longer than a minute.

.

[FUBAR]

German Autobahn, I travel a lot across Europe, usually overnight, see earlier posts for details. It's often closer to 3.5hrs at a time at 138mph, plus roadworks,some local speed limits and a short refuel stop.

The overheating gaskets I know about from the guy who chipped my Octy and Superb, it is a long term effect, hard to make it happen with UK speed limits even over 10 years. More 'popular' problem again in Germany where it is possible to load the engine to the max for longer than a minute.

.

Yea saw earlier posts just made it sound like you had found a part of the Autobahn network where you could legally sit at 138mph for over 2 hours without slowing that would be 444km LOL (I would like to find one). I drive all over Europe too and cover the A2 (E30) a lot and there are flaming loads of speed restrictions on it :( Heading east between Hanover and Braunschweig there is a 40km stretch in both directions that's 120kph and large variable speed zones and 100kph zones dotted along too, before the inevitable seemingly abandoned road works that have been in place for years. Large unlit sections at night at full pelt I tend to avoid as if deer run out (well signed) or something has fallen off a lorry, it could be horrific at larger speeds. You head through Germany to Poland then?

Not long ago I did 650km between 3am and 9am (2 smoke stops and weight in car) first half was poor visibility with mist etc so bang on the official advised maximum speed limit of 130kph on Autobahn's, return leg of 350km ish at cars ability with up and down as per the restrictions in place had over 1/4 of a tank left (2.0TDCI 140bhp Mondeo 70 litre tank) 132mph GPS (speedo greatly exaggerates in it being a Ford). You need a Mondeo Titanium X sport TDCI 200BHP, no one will steal that!

Current Octy II FL CR TDi has not been pushed all the way but has seen 153 GPS.

[jonnynewns]

We are talking 130mph almost constant speed 2hr+ runs here.

Driving that fast even on the autobahn for 2 hours is asking for trouble!

[dieselV6]

40km restriction near BS (and this time it is BraunSchweig for a change ) is not much compared to total 700km+ A40/A3/A2/A10 run, yes, you do have to slow down on a few occassions. That's why I said average 125mph, cruise 138mph. It's the limits and roadworks that drag the average down. Roadworks can be avoided in many directions if you check before trip as there are 2 or even 3 parallel routes in most directions. But once I did not check and got 8 roadworks over 50 miles of A3...

I criss-crossed Germany in pretty much every direction, A9 is very fast too, A6 used to be, then they started digging, do not know if they finished. Parallel to A2, A38 and A44 at night are ridiculous, empty at night, with a couple large refineries lit like Christmas trees and a giant open cast mining excavator by the roadside. Going north to Denmark/Sweden is not bad either, Hamburg is a pain though.

Edited 20 January, 2013 by dieselV6

[dieselV6]

Driving that fast even on the autobahn for 2 hours is asking for trouble!

My Mk1 Superb says otherwise. No trouble at all, 110k miles on the clock. You do use more fuel and tyres, though. Brake wear is not increased as long as you take foot off accelerator in good time, but it does pay to have good brakes (EBC yellows all round/ 312mm/255 mm discs, Super DOT 4 fluid).

[jonnynewns]

My Mk1 Superb says otherwise. No trouble at all, 110k miles on the clock. You do use more fuel and tyres, though. Brake wear is not increased as long as you take foot off accelerator in good time, but it does pay to have good brakes (EBC yellows all round/ 312mm/255 mm discs, Super DOT 4 fluid).

Tbh we have speed limits for a reason and I am very happy to stick to those limits where applicable, but 130mph is just being stupid no matter the conditions or the roads, especially for that length of time. Are you using GPS to verify the speed or just going off what the dial says?

[FUBAR]

My Mk1 Superb says otherwise. No trouble at all, 110k miles on the clock. You do use more fuel and tyres, though. Brake wear is not increased as long as you take foot off accelerator in good time, but it does pay to have good brakes (EBC yellows all round/ 312mm/255 mm discs, Super DOT 4 fluid).

To be fair as much as I would not subject my own car to similar prolonged bouts of flat out speed (I own a Skoda so not rich enough for all the diesel) I have had no issues doing the same in company cars come to think of it, Mondeo was only on its 2nd gear box by 14000 miles it appears they didnt fill it with enough oil in factory

[dieselV6]

Actual GPS quoted, speedo overreads by well over 8mph at these speeds.

Re speed limit making motorway safer, you should go to Sweden and see cars wavering all over the lane on the motorway because drivers cannot keep attention on empty motorway at (too) low speed. Perhaps that would give you some food for thought.

You do not have to do high speeds, it works for me though, and given that at least 3-4 German cars rapidly overtake me during the night, I am not the fastest by quite a margin.

I own a Skoda precisely so that I still have a decent fuel budget left

[Herschel]

diesel,

can I ask, what mpg do you get at an average of 125mph in Germany?

H

[dieselV6]

138mph cruise / 125mph average gave me about 12l/100km, or 23mpg. Mk1 Superb, 2.5TDI.

125mph cruise / 110mph average gave me about 10l/100km, or 28mpg. And at this speed, Octy 1.9 used marginally more fuel than Superb 2.5, both cars same gearing, wheel diameter and tyre size. It's more fun at 138mph, though

Data from fuel fill-ups over distance covered, though maxidot display is fairly accurate on the Superb (it was optimistic on the Octy).

Edited 21 January, 2013 by dieselV6