Disco 3 (LR3) Mystery of Fuel Economy

Had my D3 (2.7D, Auto-box) for about 2 years now, more usually used for the daily commute (Doncaster > Leeds (circa 35 miles (33 on motorway) motorway). The other week i decided to see if there was any significant difference in engaging 'SPORT' mode (contradication, lol) on the gearbox. I maintained my same drive style (i.e. mostly in cruise at about 65 on motorway). To my great surprise and delight, for a consistent 3 tanks work of fuel now doing this has given an indicated MPG increase of about 3-4 MPG.

Normally without 'SPORT' engaged i was getting indicated circa 32-33 MPG per tankful (approx 530 miles run per tank), but now easily achieving 35-37 MPG again per tankful. Anyone else tried this or explain this away? My driving style has not changed nor have tyres or pressures. Same roads, same traffic only difference is gearbox mode.

In town is hard to gauge as I rarely do significant in town, but I can't explain this in away, unless timing is changed in the ECU as well. I know the gears are held longer (to higher revs) in sport but on my commute this makes little effect as mostly in 6th (i guess). But based on this it's my new driving mode!

The only way to validate the claim would be to revert and see if mpg drops. Then reinstate using Sports mode and see if it repeats as an improvement.

As for why. Well if you aren’t particularly driving any differently. Then sports mode may be allowing you to reach cruising speeds quicker and more efficiently by making better use of the gears. And also by not labouring the engine so much. In sports mode it is more likely to drop a gear on an incline or keep hold of a lower gear. Rather than use the low end torque and large throttle opening s.

Driving hard in sports mode however would likely not improve mpg.

Valid Point, I'll revert on my next tankful and see what happens, and report back.

In sport or normal, I'm light on the throttle and the journey is fairly flat so acceleration, incline etc will have negligible if any effect. (M180 J1 to M62 J29 via M18, only about 2-3miles of A road total, rest is motorway constant speed in 'Cruise Control' usually). Only other factor that may come into play may be outside temperature being cooler for the past few weeks (intercooler more effective) but again I had been recording the lower MPG in normal over the past 2 years or so irrespective of temperature.

It'll be blown to hell soon anyway when temp drops below threshold for FBH to come in, that always knocks economy, that thing just drinks fuel ) Similarly I don't chase fuel economy it is a LR @ ~2.6Te after all , but every little helps. 130K on the clock I'm glad its holding up well.

Torque converter lockup will also impact mpg. I don’t know how this operates in Sport mode vs normal mode. But may be another point where this is a factor.

You must be a very very careful driver to get over 30mpg out of an auto D3?
You may also find its a placebo effect and the only true way to test it would be for you to be blindfolded, but I suspect the test might be quite short and painful!

My daily 5 miles commute gives me 20mpg, normal running about 25mpg and a long run on cruise at 70mph will eventually creep up to 30mpg.

FBH drinks 1/2 lph at full chat, then drops down to idle once temperature reached, but on short runs the thing doesnt stop heating for the entire journey.

This is my 5th Disco and what I found was as the models get newer/more powerful/heavier the economy drops from easy to get 30mpg on a 200 to the 25mpg average of the TD5/D3.

Funny I wouldn’t say 30mpg from a Tdi A Disco is easy or normal.

300bhp/ton said:

Funny I wouldn’t say 30mpg from a Tdi A Disco is easy or normal.

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May I ask how many tdi discos you have owned?

lynall said:

May I ask how many tdi discos you have owned?

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3. And driven and used maybe 10 others and other Tdi powered vehciles. Have two Tdi 200’s at the moment.

O dear another thread on a diesel owner obsessed on their vehicle MPG.

discool said:

O dear another thread on a diesel owner obsessed on their vehicle MPG.

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Indeed , also considering it has the same aerodynamic lines as a house brick , lol

I don’t even bother now looking at the mpg display , AKA , lie o meter , done a few tank fills on mine and get around 31 mpg on a run and about 22 mpg around town, well pleased considering it weighs nearly 3 ton

lynall said:

You must be a very very careful driver to get over 30mpg out of an auto D3?
You may also find its a placebo effect and the only true way to test it would be for you to be blindfolded, but I suspect the test might be quite short and painful!

My daily 5 miles commute gives me 20mpg, normal running about 25mpg and a long run on cruise at 70mph will eventually creep up to 30mpg.

FBH drinks 1/2 lph at full chat, then drops down to idle once temperature reached, but on short runs the thing doesnt stop heating for the entire journey.

This is my 5th Disco and what I found was as the models get newer/more powerful/heavier the economy drops from easy to get 30mpg on a 200 to the 25mpg average of the TD5/D3.

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Hi mate

Most I’ve got on a run is 32mpg , of course don’t take any notice of the onboard mpg display

Same around town, roughly 20-22 mpg, indeed winter time does drop

Must admit haven’t heard that before in getting 35-37mpg in a D3

gstuart said:

Hi mate

Most I’ve got on a run is 32mpg , of course don’t take any notice of the onboard mpg display

Same around town, roughly 20-22 mpg, indeed winter time does drop

Must admit haven’t heard that before in getting 35-37mpg in a D3

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Rough rule of thumb with the dash mpg widget is knock of 10 percent and you wont be far out

300bhp/ton said:

3. And driven and used maybe 10 others and other Tdi powered vehciles. Have two Tdi 200’s at the moment.

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I raise your bet to 5 discos
1 x 200 covered approx 40k
2 x 300 one did about 20k other 50k
1 x td5 covered 50k
1 x D3 covered 30k so far

I also have two 200 powered motors as well, I bet you also have a spare injector pump and at least one cyl head? I know I have!

I realise everyone will get different results depending on where they live and how they drive, but I think with the miles I have covered my mpg results are typical of the breed.

gstuart said:

Hi mate

Most I’ve got on a run is 32mpg , of course don’t take any notice of the onboard mpg display

Same around town, roughly 20-22 mpg, indeed winter time does drop

Must admit haven’t heard that before in getting 35-37mpg in a D3

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Im sure over 30mpg is possible, anything is if you try hard enough.
I can understand plus 30 from a manual version but from an auto that takes serious commitment.

lynall said:

I raise your bet to 5 discos
1 x 200 covered approx 40k
2 x 300 one did about 20k other 50k
1 x td5 covered 50k
1 x D3 covered 30k so far

I also have two 200 powered motors as well, I bet you also have a spare injector pump and at least one cyl head? I know I have!

I realise everyone will get different results depending on where they live and how they drive, but I think with the miles I have covered my mpg results are typical of the breed.

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30mpg in a Disco is possible. Usually on stock non smoky tdi’s But you still need to be on a run to attain it. Normal driving is unlikely to result in that level of mpg. Tdi is more 24-27 average.

Td5’s are similar. My Uncle happens to have 2 stock Td5 Discos, both manuals. One on a Y plate the other a few years younger. The Y plate one is very frugal and on a run will do over 600 miles to a tank with relative ease. Over 30mpg. The other one however is far more lively but struggles to better 26mpg.