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Crusing at 80mph on a motorway for the majority of the journey - is there going to be a vast difference in mpg between diesel and petrol? I can't seem to find any info.
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Crusing at 80mph ........
Naughty, naughty!
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I would say 15mpg in favour of diesel
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I would say that the diesel will be less stressed at motoroway speeds.
I can confirm that the fuel usage between an Astra 1.6l Petrol and a Kia Rio 1.5l Diesel was alot more with the astra.
I could use a quater of a tank to do 18 miles at motorway speeds (with some steep hills).
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I could use a quater of a tank to do 18 miles at motorway speeds (with some steep hills).
Do you know you that is about 6 mpg?
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It depends on the cars being compared.
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It will vary tremendously with gearing having a big influence. Assuming roughly same size, weight and aerodynamics, a six speed box with a petrol engine will get close to a 5 speed diesel say within 10%. A low geared six speed diesel could easily be 30% more efficient than a low geared 5 speed petrol. I had a 2 litre petrol Mondeo that would give 36-38 mpg crusising at 80 'ish and a diesel Picasso that would just manage over 40mpg on the same run, both 5 speed. A VAG PD engine with a six speed box would be difficult to beat.
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Depends on a lot of factors. Petrol cars with a 6th gear are revving a lot less than those with 5 gears. E.g. mine is doing less than 3000 revs at 80 (allegedly!). Diesel cars are more expensive to buy in the first place generally and then diesel is more expensive than petrol - lots of variables!
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Even with the same model of car the gearing can be different, even with the same engine! An example would be the 1.4TDi80 Fabia, the standard Fabia is geared so it runs at about 500rpm more in 5th than the Blueline, which seems to use the 1.9TDis gear ratios... so obviously at 80 the blueline will use less fuel... but at that speed things like headwinds, etc have a lot more effect on mpg than many people would admit...
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If I were to travel the 18 miles at 80mph and push it in every gear then it would use a quater of a tank (full tank was 52 litres).
At worst case I averaged 34mpg over a tank full.
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I don't know if another engine exists that matches the efficiency of the VAG PD at a motorway cruise.
If I reset the Golf's computer on the motorway, and drive at a steady indicated 80 mph, the average settles at around 62 mpg. Based on what I know from calculations over a full tank against computer readout, that's a genuine 56 mpg. I would be surprised if an equivalent output petrol engine in a car of similar weight and aerodynamics would get within 15 mpg of that.
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Oh my excuse my ignorance but what's a VAG PD engine. BTW I'm looking at Primera diesel 2.2cdi or di
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Perhaps if you're that interested in economy, doing ~60mph M-way speeds (in either type)
might be more pertinent & effective?
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>>Oh my excuse my ignorance but what's a VAG PD engine. BTW I'm looking at Primera diesel 2.2cdi or di"
VAG PD engine is the previous generation Volkswagen-Audi Group diesel engine
Commonly know to be very punchy and frugal - so great fuel economy although known to be slightly optimistic on the OBC.
They are slowly being replace across the golf / audi / skoda range (skoda getting the new engine now being the last) with the new common rail varients which have less vibration, less diesel clatter, run a bit better on emissions and nox/particle emissions and supposedly better power and torque across the rev band; at the expensive of being excessively complicated and expensive.
Edited by OldSkoOL on 29/04/2009 at 11:46
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Having a vehicle fitted with a PD engine, I can vouch for its exceptional efficiency.
It's best to look at actual gear ratios before assuming that a 6 speed box will give significant cruising economy gains. My car (Passat clone) was made with 5 and 6 speed boxes - the 6 speeder attracted a significant price penalty. Mine is geared at 33 mph/1000 rpm in top, the 6 speeder is 35. This means that at 70 mph in the highest ratio for each box, the engine fitted to the 6 speed gearbox is turning all of 120 rpm more slowly.
A PD engine has such a broad spread of torque, 6 speeds are unnecessary - it's just a clever marketing ploy with instant "cabin appeal".
By the time the Govt. have finished lowering speed limits all round, 3 speeds will be enough. The days of a legitimately ratioed 6 speed box will soon be over in the UK.
659.
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supposedly better power and torque across the rev band; at the expensive of being excessively complicated and expensive.
VAG went the common rail way to reduce the costs, one large pump is cheaper to produce than 4 smaller pumps.........................................
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Its a noisy little so and so, though... in a nice gruff way!
My Roomie's geared at 29mph/1000rpm in 5th, same as my old Mk1 Fabia 1.9TDi, btw.
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I suspect emissions played a part too. The PD's are the only semi-modern diesels you see on the road nowdays that puff visible smoke in general driving. Sit behind one at the lights and you'll see (and smell) it leave a haze behind it even under fairly gentle acceleration.
I've always thought this characteristic to be slightly at odds with some of the hugely expensive "prestige" cars the engine has been installed in over the years.
Great engine though.
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