Evening all. After a reset of the cars trip computer following a battery disconnect, I notice the mpg is poor.
I recently thought I’d been burning through a lot of diesel recently, but not bothered enough to investigate further.

The car recently had a new serpentine belt, with alternator, water pump and ac compressor, followed by a coolant flush. And today I gave the car an oil change, new filters, and also popped the MAP sensor out for a clean (it was gunked up).

On a typical drive this evening I managed to get a total of 24mpg with a very gentile drive between 40 and 60. This is a journey where I should be getting nearer 30mpg. This is the same mpg as when I had a 5l supercharged fattie!

When I did the oil change I did have a look around the oil filter and plenum, but couldn’t see any signs of oil or misting anywhere so don’t think I have a leak there. The car seems to drive well, and is still smooth running. I have no smells of oil or diesel in or around the car.

Any suggestions as to what could be causing this?

I am planning on removing the throttle body and plenum at some point soon to clean out the gunk which may help… Currently driving: 2012 L322 SE Overfinch 4.4 tdv8

Past rides:
2014 Audi Q7 3.0d (good riddance)
2010 L322 Autobiography 5.0 Supercharged
2011 L320 HSE 3.0 sdv6
2014 Jaguar XF-RS 5.0 supercharged
2007 BMW 535D
2005 Mini Cooper S

https://www.fullfatrr.com/forum/topic59478.html

If your car is having problems regenning the DPF, then it will use more fuel to initiate repeated burns. May not be your problem but I had poor MPG when my 2011 had DPF probs caused by a faulty thermostat keeping the engine too cool.

Don’t trust the mpg on the trip readout to be accurate esp after a reset. The only way to be sure is to divide distance between fill ups with gallons of fuel put in. 2012 TDV8 Vogue (L322)

Cheers JayGee
I’ve never trusted the on board mpg figure, but have been happy using it as a guide. My belief was that while not accurate, it was at least fairly consistent. I tend to not show it, and only noticed the low number as I was cycling through the display options.

Does a reset affect that displayed figure? Does it become more accurate after some time?

Unfortunately I brimmed the tank the other day so… actually I’m being an idiot. I’ll brim the tank (again) today and will reset the trip so I can get an accurate figure.

She still “feels” more thirsty. That fuel gauge seems to be moving at s/c speeds… Currently driving: 2012 L322 SE Overfinch 4.4 tdv8

Past rides:
2014 Audi Q7 3.0d (good riddance)
2010 L322 Autobiography 5.0 Supercharged
2011 L320 HSE 3.0 sdv6
2014 Jaguar XF-RS 5.0 supercharged
2007 BMW 535D
2005 Mini Cooper S

https://www.fullfatrr.com/forum/topic59478.html

Dolphinboy wrote:

If your car is having problems regenning the DPF, then it will use more fuel to initiate repeated burns. May not be your problem but I had poor MPG when my 2011 had DPF probs caused by a faulty thermostat keeping the engine too cool.

That’s a good shout. There’s a great thread on dpf and regens so I’ll look at what to monitor on my IIDTool to see my soot level.
My general drives include stints where the dpf regen should kick in, so expect my level to be low. This may give a clue and worth a check.  Currently driving: 2012 L322 SE Overfinch 4.4 tdv8

Past rides:
2014 Audi Q7 3.0d (good riddance)
2010 L322 Autobiography 5.0 Supercharged
2011 L320 HSE 3.0 sdv6
2014 Jaguar XF-RS 5.0 supercharged
2007 BMW 535D
2005 Mini Cooper S

https://www.fullfatrr.com/forum/topic59478.html

I forgot to mention, I checked my brakes too last night.
The fronts were warm/hot to the touch as expected but the rears were only slightly warm. The rear left was slightly warmer than the right, only slight. If I had a sticking calliper I would expect it to be hot, so am not concerned with that.
Also the car drives true, with no pulling.

I am planning on a gearbox oil change next month, and will do the diffs and transfer box also. The car is at 120k and do not believe they’ve been changed at any point. Currently driving: 2012 L322 SE Overfinch 4.4 tdv8

Past rides:
2014 Audi Q7 3.0d (good riddance)
2010 L322 Autobiography 5.0 Supercharged
2011 L320 HSE 3.0 sdv6
2014 Jaguar XF-RS 5.0 supercharged
2007 BMW 535D
2005 Mini Cooper S

https://www.fullfatrr.com/forum/topic59478.html

What’s your miles remaining on the trip after a fill? On light load a partially blocked intake or dpf won’t kill mpg as there is not enough airflow for a restriction to be significant. There is input from GPS as the nav has a calibrate after tyre change function in the settings. Are you running stock tyre sizes? 2012 TDV8 Vogue (L322)

The DPF regen frequency theory affecting MPG is a good one but I can demonstrate it's not having an effect - apols I don't want to seem contradictory!!

I had a DPF that regenned every 50-60 miles (bigger + different topic, the long and short of it was the matrix was knackered after the car had been driven through a salt water ford on the Isle of Man then left standing!!!).

I put a new DPF and Cat on (I think I am the only person to have done this). My DPF now regens about every 340 miles.
MPG was the same before and after (October 2021). Incidentally I brim the tank and work the MPG out manually. some of these are motorway journeys, it's pretty much the same (and less than the dash, range 22-40mpg and average 28mpg). I have also had the engine out, new injectors and basically everything you can think of with a very experienced ex-LR Chief Tech rebuilding the engine as standard with no mods. Below is my MPG before and after new DPF.


Maybe clean your MAF and MAP sensors in case they are making you overfuel.
On another note, it would be great if someone else would measure mileage vs fuel from the pump to compare...
N.B. - I only use Premium Diesel - I was Shell but in the course of solving the DPF issue changed to Esso in case the Shell tank was contaminated - that's how far down the rabbit hole we went!
Tyres 255/50 R20








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Last edited by Range Rover L322 on 5th Feb 2022 11:47pm. Edited 2 times in total

Once did a brim to brim after 200miles mainly on the M-way and got 32mpg. 2012 TDV8 Vogue (L322)

Once did a brim to brim after 200miles mainly on the M-way and got 32mpg. 2012 TDV8 Vogue (L322)

I’m only getting 24/25 mpg but short runs of circa 10 miles so I would suggest about right. These are measured and recorded brim to brim. Live on side of a hill so going one way it’s 1/2 mile climb fro cold that unfortunately is the most common journey. Other car is a Kia Niro and it fluctuates by up to 10 mpg depending on journey.

Put a tank of premium diesel in last fill so will see how that goes. 2012 tdv8 Westminster arrived Jan 19 gone Dec 23

200 TDi discovery bobtail gone
RR classic v8 bobtail gone
300 tdi Discovery 3 dr gone

I would suggest any real mpg north of 25mpg on mixed driving is not bad given a 4.4 V8 pulling 2.7tonnes….
Been doing some adjustments to the CCF instrument pack settings to do with tyre sizes. Noticing a possible change in the gearbox shift points i.e not holding gears as long on going up hills and consequently keeping revs down which may be interesting….. 2012 TDV8 Vogue (L322)

JayGee wrote:

What’s your miles remaining on the trip after a fill? On light load a partially blocked intake or dpf won’t kill mpg as there is not enough airflow for a restriction to be significant. There is input from GPS as the nav has a calibrate after tyre change function in the settings. Are you running stock tyre sizes?

I’ll fill up today, and will check. I used to get over 500 remaining on a tank so will see soon.
That’s a good point regarding airflow. My journeys have been light on the throttle and not using the big turbo.. unless it’s really bad of course

I’m not on stock… my rolling profile is larger than stock, but I have adjusted as best I can in the IIDTool. 60mph shows 58 on the dash. I have been running on these tyres for months and hadn’t noticed a change in fuel consumption. But I will be mindful as I may not have noticed before now… Currently driving: 2012 L322 SE Overfinch 4.4 tdv8

Past rides:
2014 Audi Q7 3.0d (good riddance)
2010 L322 Autobiography 5.0 Supercharged
2011 L320 HSE 3.0 sdv6
2014 Jaguar XF-RS 5.0 supercharged
2007 BMW 535D
2005 Mini Cooper S

https://www.fullfatrr.com/forum/topic59478.html

Range Rover L322 wrote:

Maybe clean your MAF and MAP sensors in case they are making you overfuel.
On another note, it would be great if someone else would measure mileage vs fuel from the pump to compare...

JayGee wrote:

I would suggest any real mpg north of 25mpg on mixed driving is not bad given a 4.4 V8 pulling 2.7tonnes….
Been doing some adjustments to the CCF instrument pack settings to do with tyre sizes. Noticing a possible change in the gearbox shift points i.e not holding gears as long on going up hills and consequently keeping revs down which may be interesting…..