Disco 2 15mpg????

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Just got back from a hol in Inverness. Done nearly 1,700 miles and returned 30mpg on very varied driving. TD5 with auto box. When I brim it, as in until the fuel is at the top of the neck of the filler, the gauge doesn't even move for about 120 miles. Then it's quite predictable.
 
Well I filled up and drove to Leicestershire and back. Doing around 70mph on the motorway. 136 miles since I filled it up.

Filled up again to the top with 29 litres/6.4 gallons

Comes to 21mpg. Still not brilliant :(
 
Definitely does not seem right,

I average 28 MPG, Doing a variety of different driving , including a bit of heavy footedness.

Cheers
 
So what would you expect with that roof rack filled with spots and that bar with spots which restricts more than half of the flow through the intercooler though...btw what tyres are you running?, cos if they are greater than std that 21mpg is too good IMO... my consumption increased from 28 to 23mpg on motorway only because i fitted 3.5% greater tyres(255/70/16 instead of 255/65/16)...and i dont have anything additional on the body...btw turn that snorkel's intake backwards if you drive on motorways... are you doing lot of wading with those road tyres? :rolleyes:

i strongly recommed you to fit an EGT gauge
 
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V8 shooter said:
Just checked the mpg (properly) on my auto v8.... 17.6! Over 300 miles of which about 200 were motorway at 65-70mph so I guess that's as good as gets!
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That is OK for me I've always assumed 18mpg average when working out fuel cost go a long distance trip, I then decide to fly, :)
Although a couple of years or so ago I went on a 220 mile trip to Devon and although it was A2, M25, M3 and A303 it took seven hours, anyway the average mpg was 21.8.
But the quick home drive was M5. M4. M25 and A2 did that in 4 hours, but only when I got past the D2 and its caravan that both had fallen over on the M5, it took me 1.5 hours in traffic to get past that, so then pedal to the metal and 100+ and outside lane where I could, after that all that it returned 18 mpg so no bad at all.

I should have used my 4.2 V8 Quattoporte on this trip as that showed 36 -38 mpg on the dash display sometimes... but them dropping when flat out to 8, much faster than my bro's XF, and it's the reason I bought it. Four years on I part x :D
 
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Landshandy said:
Well I filled up and drove to Leicestershire and back. Doing around 70mph on the motorway. 136 miles since I filled it up.

Filled up again to the top with 29 litres/6.4 gallons

Comes to 21mpg. Still not brilliant :(
Click to expand...
I've had a flick through the earlier pages on this thread. Have you ever confirmed what engine and gearbox you have?

i.e.
V8, Td5, manual or auto?


Has the vehicle been mapped at all? Does it smoke or drive well?

How were you measuring 70mph? Was it GPS, or speedo?

Are you sure you refilled to the same level?

If you've had a fuel leak previously, then this could still be an issue, by the very fact you are saying it is using a lot of fuel.

If anything is binding that may cause worse mpg. And do you have air con? It is not unknown for the aircon compressor to run at full tilt, this will use more fuel.
 
Not really. I suspect they don't restrict anywhere near that in reality. Thermal dynamics is a rather interesting and complex thing.

Also at cruise speed and throttle openings, you shouldn't me making high boost, so the AIT's will not be massively higher. And as a rule, warmer intake air will promote better mpg.

But I don't see any relevance of an intercooler and mpg.
 
300bhp/ton said:
Not really. I suspect they don't restrict anywhere near that in reality. Thermal dynamics is a rather interesting and complex thing.

Also at cruise speed and throttle openings, you shouldn't me making high boost, so the AIT's will not be massively higher. And as a rule, warmer intake air will promote better mpg.

But I don't see any relevance of an intercooler and mpg.
Click to expand...

Still not convinced that having a fat bull bar and huge spots in front of the rad and intercooler is going to enhance performance. :D

And sierraferrys point about wind resistance, and its effect on fuel economy, is completely valid. Those spots will completely break up the airlflow as it starts to pass over the vehicle, and then the flow hits the effective air dam formed by the roof rack and mahoosive spots.
Snorkel is huge as well, and not very streamlined.

I suggested as much in a joking sort of way in post 2! :)

"To be fair, you could hardly design anything for more wind resistance than that! :eek: :D"
 
300bhp/ton said:
Not really. I suspect they don't restrict anywhere near that in reality. Thermal dynamics is a rather interesting and complex thing.
Click to expand...

I know when I took the daft spots off my D1 within seconds of buying it, it made a difference to both performance, and MPG. Given the IC is behind the spots, and said spots have broken the intended airflow, I reckon it'll be a significant effect. And this will be worse with a full width IC.


300bhp/ton said:
Also at cruise speed and throttle openings, you shouldn't me making high boost, so the AIT's will not be massively higher. And as a rule, warmer intake air will promote better mpg.
Click to expand...

I agree that warmer air will promote better MPG, but only if the IC can do its job - if the IC is obstructed, then this won't apply. the performance of the full width in mine is noticeably different (better) on a hot day. Any "brick" doing 70MPH is going to need some boost on to make the power to push all the air out of the way - if said brick is less aerodynamic, then, clearly, it'll need more power ( and thus boost ) to make it "go", and the OP's D2 is way less aerodynamic that standard....

Mine runs about 3/4 bar at 70, rising to full up a hill, and EGT's can be 450 - 500 C - so its working pretty hard.

300bhp/ton said:
But I don't see any relevance of an intercooler and mpg.
Click to expand...

No offense, but drive a diesel with a full width for a few years and you will. Unless I misunderstand your point?
 
300bhp/ton said:
Also at cruise speed and throttle openings, you shouldn't me making high boost, so the AIT's will not be massively higher. And as a rule, warmer intake air will promote better mpg.
Click to expand...
If you name AIT the IAT and speaking about Td5 you are wrong, do you know where the IAT is measured on Td5?...at higher IAT the combustion is worst so the driver to keep the speed/boost steady must push the throttle which will result in higher fuel consumption cos the fuel delivery on driver demand is much more higher than then addaptive strategy's fuelling management....that would happen with higher ECT(engine coolant temp) too which at that restriction in front of the radiator is obvious for me.
 
sierrafery said:
So what would you expect with that roof rack filled with spots and that bar with spots which restricts more than half of the flow through the intercooler though...btw what tyres are you running?, cos if they are greater than std that 21mpg is too good IMO... my consumption increased from 28 to 23mpg on motorway only because i fitted 3.5% greater tyres(255/70/16 instead of 255/65/16)...and i dont have anything additional on the body...btw turn that snorkel's intake backwards if you drive on motorways... are you doing lot of wading with those road tyres? :rolleyes:

i strongly recommed you to fit an EGT gauge
Click to expand...

I've got 235/85/16 general grabbers on as I'm off to Morocco and the Sahara for 5 weeks so no road tyres
 
300bhp/ton said:
I've had a flick through the earlier pages on this thread. Have you ever confirmed what engine and gearbox you have?

i.e.
V8, Td5, manual or auto?


Has the vehicle been mapped at all? Does it smoke or drive well?

How were you measuring 70mph? Was it GPS, or speedo?

Are you sure you refilled to the same level?

If you've had a fuel leak previously, then this could still be an issue, by the very fact you are saying it is using a lot of fuel.

If anything is binding that may cause worse mpg. And do you have air con? It is not unknown for the aircon compressor to run at full tilt, this will use more fuel.
Click to expand...

Yeah it's a TD5, auto, stage 1 remap, speed measured off the speedo
 
Reading back through this thread a number of questions come to mind:
  1. Regarding that fuel leak, are you absolutely sure that it has been repaired correctly?
  2. Regarding the "stage 1 remap", who did it and are the figures correct?
  3. Owing to your apparent penchant for "bolt on, go faster" extras, do you have any "flea-bay fuel saver booster boxes" fitted to the engine?
  4. Are you sure that you aren't getting an unusual amount of slippage in the auto transmission?
  5. Your fuel figures are based on a speed of 70mph by the look of it. What are they like at a steady 56mph?
 
Landshandy said:
Yeah it's a TD5, auto, stage 1 remap, speed measured off the speedo
Click to expand...
Right, so lots going on here, most really obvious though ;)

You are on BIG tyres, a lot bigger than stock.

This means:

-your speedo is wrong
-your odo is wrong

You need to allow for these errors in your calculations.

Auto's are less economical.

And a mapped car is likely to be less economical than a standard one.


This means an over geared Disco auto running at what was more likely 80mph, which means high rpm's, with HUGE aero drag compared to stock and mapped to 'add' more fuel.

I'd say low 20's is probably about right from such a vehicle. More sedate driving at 50-55mph it'll probably be nearer to a stock auto. But they aren't exactly rated as high mpg cars anyway.

Also you are covering more miles than your odo is probably recording. So your calculation is wrong.

I'll let you work out the tyre size difference, suspect it's more than 5%, but less than 10%.

But even so it means your mpg figure is probably 2mpg out. So a high speed blast in a mapped auto Disco with a large sail on the roof. 24mpg'ish is pretty ok.
 
300bhp/ton said:
Right, so lots going on here, most really obvious though ;)

You are on BIG tyres, a lot bigger than stock.

This means:

-your speedo is wrong
-your odo is wrong

You need to allow for these errors in your calculations.

Auto's are less economical.

And a mapped car is likely to be less economical than a standard one.


This means an over geared Disco auto running at what was more likely 80mph, which means high rpm's, with HUGE aero drag compared to stock and mapped to 'add' more fuel.

I'd say low 20's is probably about right from such a vehicle. More sedate driving at 50-55mph it'll probably be nearer to a stock auto. But they aren't exactly rated as high mpg cars anyway.

Also you are covering more miles than your odo is probably recording. So your calculation is wrong.

I'll let you work out the tyre size difference, suspect it's more than 5%, but less than 10%.

But even so it means your mpg figure is probably 2mpg out. So a high speed blast in a mapped auto Disco with a large sail on the roof. 24mpg'ish is pretty ok.
Click to expand...

I realise the tyres will affect the mpg but when I made the original post it had 18" on.
 
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