Author Topic: Poor Diesel PD Fuel Economy?  (Read 1085 times)

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Poor Diesel PD Fuel Economy?
« September 05, 2018, 13:05:36 »
I was expecting my new PD to be significantly more economical than my old FD.
It isn't.
Both were bought new and have similar performance, dimensions and specifications (UK 6 speed 1.6 crdi hatchback).
The type of motoring is the same.
At 27,000 miles the overall average of the FD was 61.9 mpg. At the same mileage the PD has averaged 62.9 mpg.
However, the stated fuel consumption figures for the combined cycle are 62.8 mpg for the FD and 74.3 mpg for the PD.
Ultimately the economy of my FD beat the combined cycle figure by reaching 63.3 mpg. At present my PD is well below even the urban cycle figure of 67.3 mpg.
Is there something wrong with my PD?
Since an ecu and lambda sensor service campaign the Malfunction Indicator Light has stayed off and at its first service the independent that also maintained the FD found no faults.
One thing that I have noticed is a 1,250 rpm glitch causing a little hesitation when accelerating.
I would be interested to know if others who went from an FD to a PD noticed an improvement in fuel economy.
Also, the most I've fitted into the 50 litre fuel tank is 55 litres, has anyone managed more? 



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Re: Poor Diesel PD Fuel Economy?
« Reply #1 : September 05, 2018, 17:16:19 »
Jeepers Marti, I see where you are coming from, but it is the same engine after all. Hard to  call 60+ MPG poor.  :eek:
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Re: Poor Diesel PD Fuel Economy?
« Reply #2 : September 05, 2018, 17:27:42 »
Hard to  call 60+ MPG poor. 
Plus what the computer tells you is not necessarily spot on either. If you are so concerned, do the proper thing and brim your tank every fill-up and keep record of the miles and fuel over an extended period of time. That will give you accurate figures that can be believed without question.
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Re: Poor Diesel PD Fuel Economy?
« Reply #3 : September 06, 2018, 10:50:22 »
I'm a 'spreadsheet brimmer' when it comes to fuelling, keeping people waiting whilst I squeeze in every last drop and then recording the mileage and quantity.
The dashboard displays are inaccurate, the FD overstated the economy by about 3.3 mpg whilst the PD understates by about 3.7 mpg on the accumulated setting. The figures I use are my own which as an accountant I consider far more reliable.
Stated fuel consumption figures are for comparison purposes only. I'm comparing one i30 against another and feel that if I can more or less match the combined figure in one car then all other things being equal (which I think they are) then I should be able to match the combined figure in the other.
Incidentally, I kept a couple of previous cars (Ford Focus and Rover 414) for about 190,000 miles each. Both were 16 valve, 5 gear manual petrol and each one matched or slightly exceeded its claimed fuel consumption.
So I still wonder why the economy of my PD is so far below expectations and how others compare. Although the PD is similar to the FD there are about 8 years of research and development between them and the newer model should be significantly more efficient.

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Re: Poor Diesel PD Fuel Economy?
« Reply #4 : September 06, 2018, 18:20:46 »
Ok, I stand corrected. Looks like my usual breakfast of porridge and yoghurt is going to be replaced by humble pie this morning...  :snigger:
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Re: Poor Diesel PD Fuel Economy?
« Reply #5 : September 06, 2018, 18:25:38 »
What he ^ said...
Would help though to mention spread sheet figures in the first post ;)
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Re: Poor Diesel PD Fuel Economy?
« Reply #6 : September 06, 2018, 19:59:19 »
Auto or manual?
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Re: Poor Diesel PD Fuel Economy?
« Reply #7 : September 07, 2018, 12:18:31 »
My apologies too but as I'm 'that guy' with all the numbers I thought you would know what I'm like. I also assumed that by mentioning 6 speed you would know that they're manual. By the way: I spell it yogurt without the h (as a slow typist this saves valuable seconds).
From memory a recent road test by a magazine (possibly Auto Express) of the equivalent new Kia Ceed achieved about 70mpg when touring. Virtually all of my motoring consists of long journeys at (in my opinion) sensible speeds. I think I do drive economically and this is supported by the mpg my other cars have returned and the mileage that the FD brake discs and pads lasted (190,000 rear and 200,000 front).
My PD seems to have good days when the (inaccurate) display for that day shows mid 60s mpg and bad ones when for no apparent reason it's in the low 50s mpg. There's also the 1,250 rpm falter. It's not used every day but each day that it is it goes at least 100 miles. Leaving the Pyrenees during the summer the display showed 99.9 mpg for over 40 miles (but it was downhill).

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Re: Poor Diesel PD Fuel Economy?
« Reply #8 : September 07, 2018, 17:53:52 »
Yeah the spell checker tried to make me to drop the "h"... I even googled to make sure i wasn't losing the plot!  :snigger:

I forgot you were "that" guy temporarily.  :-[

We only just started to get the DPF with the Diesel over here, but both yours would have had it I reckon. The low points sounds like DPF regeneration periods.  :cool:
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Re: Poor Diesel PD Fuel Economy?
« Reply #9 : September 10, 2018, 11:21:58 »
The PD has a DPF and the Irritating Stop Go feature. My FD had neither.
I try to remember to disable the ISG as I would rather pay for an extra drop of diesel now than for a new battery and starter motor later.
In my opinion the ISG and DPF shouldn't make much difference to my overall fuel consumption as most of my driving is long journeys on main roads, which should be economical for a diesel.
Also, I put little store on single figures, trips and tank fills, which is why I've quoted the mpg over 27,000 miles. For me it's the overall figure, trend and comparison with the FD and stated figures for the PD which are important.
Just to add a little perspective: if the PD were returning an extra 10 mpg (which is what I was expecting based on my experience with the FD and the quoted figures) then my fuel cost would be about 1p per mile lower. Over 20,000 miles this adds up to 200 which covers the cost of a service (which I have done every 20,000 miles).

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Re: Poor Diesel PD Fuel Economy?
« Reply #10 : September 10, 2018, 17:29:48 »
The PD has a DPF and the Irritating Stop Go feature. My FD had neither.
I try to remember to disable the ISG as I would rather pay for an extra drop of diesel now than for a new battery and starter motor later.
In my opinion the ISG and DPF shouldn't make much difference to my overall fuel consumption as most of my driving is long journeys on main roads, which should be economical for a diesel.
Also, I put little store on single figures, trips and tank fills, which is why I've quoted the mpg over 27,000 miles. For me it's the overall figure, trend and comparison with the FD and stated figures for the PD which are important.
Just to add a little perspective: if the PD were returning an extra 10 mpg (which is what I was expecting based on my experience with the FD and the quoted figures) then my fuel cost would be about 1p per mile lower. Over 20,000 miles this adds up to 200 which covers the cost of a service (which I have done every 20,000 miles).

The "official" mileage figure of around 74 Mpg is obviously misleading, but the fact you now have a DPF when you didn't before and that you disable the ISG on a regular basis would partly explain the "disappointing" fuel economy.

Don't get me wrong. I liked the way "ISG" worked in the two Hybrid vehicles I had, but understand the Hyundai system on the Diesel is different by necessity and quite clunky in its operation. However, the DPF regenerations do burn extra fuel to "burn off" the soot. SO, that does explain the results.

With respect, you said they should have developed improved technology to increase economy by now. In its best form I think ISG can save a bit, but HYundai don't seem to have perfected theirs yet.
  • '19 Hybrid Camry & '19 Kona Active 1.6 (Prev had four i30's incl SR and CRDi)

 


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