Fuel Consumption

[Mark O]

2008 T180 has always - according to the OBC anyways - returned around 38 mpg average using the higher grade of diesel available.

Over the past weeks however it has taken a bit of a dip, returning about 34 mpg.

Any clues as to how to restore performance would be greatly appreciated.

Work done so far

• Oil and filter changed out 2 weeks ago, as were front discs and pads 
• EGR cleaned out, new air and fuel filter done around 6 months ago
• Tyre pressures checked and in order.

Anything else perhaps?

Thoughts include clogged Injectors, but not sure how to deal with those in a fairly simple manner. Not keen on removing them.

DPF - becoming clogged perhaps?  Again not sure how to deal with that save replacing it - which seems excessive and costly.

Otherwise, engine performs well and still pulls like a train.

Cheers in anticipation

Mark

 

 

 

  

[daveh_rav4]

Hi Mark

Two things worth checking... as you have had the discs and pads changed recently this normally entails the caliper hydrolic cylinders having to be pushed back into the caliper housing to accomodate the new thicker pads and discs.  Make sure the new cylinder position is not causing the brakes to bind and theirby increase fuel consuption. Each wheel should spin freely when jacked up... apply the brakes firmly, preferably with the engine running (so the brake servo is working), release the brakes and each wheel should spin freely with little resistance.  New brakes can hang up for a while until they have burnt in and 'married' themselves to the discs but should be free after a few miles use. The usual cause is the cylinders working in a new position in the caliper and possible the pads binding in a (dirty/dry) caliper housing.  White crease can help here if applied sparingly to clean contact/moving surfaces.  Good mechanics will do this as a matter of course... but if a quick bodge job is done, then it will normmaly get left and the new pads just jammed in with all the old brake dust and grime :(  Most cars will gently roll if on a slight incline with the brakes released; if yours won't, then it's worth checking for this.  If it is just one brake binding, it will normally cause a slight pull on the steering when driving in a straight line (not to be confused with a road camber pull)  Also, if you have bashed a kirb recently then have the wheel alignment (tracking) checked; this can also increase fuel consumption if it is out (and cause excessive tyre wear).  A good indicater is if your steering wheel has changed it's straight ahead position and if you can see any sign of 'feathering' across the tyre tread width.

D'oh, I used to be a workshop vehicle tester years ago... but  I build PC's now, but not sure which is the bigger headaches LOL

Dave

[Heidfirst]

it's probably just the cold weather & possibly the change to winter fuel composition.

[Mark O]

Brakes not binding - and increase in consumption occurred before the change of pads/discs.

Another thought was cleaning the MAF sensor......if i knew how! Clues anyone?

[daveh_rav4]

Oh, I forgot... "yer up north!"  Weather down south is just like summer (still)... :)  If winter is a com'in, it ain't showed yet!  Mind you a differencial of 4mpg is not a drastic amount and would need to averaged and compared over a set milage (before and after) over similar driving conditions... could even be down to some agressive driving for a while.  If I push my Freesport Rav4... I can here the fuel being sucked out of the tank LOL.  I wish I had a pound for every Range Rover that I have left in the dust... this !Removed! goes almost as good as my old XR2.

[Anthony Poli]

2 hours ago, Mark O said:

Brakes not binding - and increase in consumption occurred before the change of pads/discs.

Another thought was cleaning the MAF sensor......if i knew how! Clues anyone?

The MAF sensor is not too bad to get to, it is either next to or inside the air filter box. On my old corolla it looked a open at one tube about 2-3" and inside there is 2 thin wires and they can get covered in dust/dirt. From what I have read you can use carburettor  cleaner, or a can of air duster. After you give it a blast, the wires should go from fuzzy to clear. 

When i had a go at mine, the car used to die when coming to a junction.

 

[Mark O]

I am indeed up North - considerably so in fact, and Winter is most definitely upon us - minus 10 just up the road last night.....However fuel consumption was comparatively poor even in the tropical autumn balm of plus 16 not too long distant.

I realize it is not much of a difference, but something is going on nevertheless. Driving style hasn't changed, and I don't - usually - floor it.  

My other thought is the Shell Nitro - the super diesel if you will - I usually use is not actually Nitro, but the normal stuff instead. That would certainly account for the difference.  

[IanML]

As Heidfirst said, it could be due to the winter fuel formulation - diesel sold in the winter months is differently formulated to prevent it going slushy.  The oil companies probably change over before the cold weather strikes.

[yossarian247]

On 11/23/2016 at 9:28 AM, IanML said:

As Heidfirst said, it could be due to the winter fuel formulation - diesel sold in the winter months is differently formulated to prevent it going slushy.  The oil companies probably change over before the cold weather strikes.

https://en.wikipedia.org/wiki/Winter_diesel_fuel#United_Kingdom

The UK officially changes over to winter diesel from 16th November to 15th March each year according to Wikipedia, but ISTR there's nothing to stop filling stations supplying winter grade fuel outside that date range if they wish. They just aren't allowed to supply summer diesel in the winter.

[Mark O]

The issue manifested itself around beginning of September - too early for winter fuel formula perhaps - especially considering the balmy weather.

[Mark O]

Chaps

 

Update on this...decided to clean out the EGR valve again today. I could not see anything else amiss and I think my diesel theory is somewhat unlikely. Disassembling the EGR valve was surprising considering it was only 8 months or so after cleaning it out last. Another build up of soot/crud. Ports however were not blocked, but considerable amounts of soot around the inside faces. Valve itself and the valve seats had soot build up. Cleaned it all out again - this time removing the solenoid to lightly oil the valve piston rod, the return spring and the valve guide over which the valve moves inside the valve chamber. Cleaned up the seating faces as best I could, and cleaned the pipe to the block. Reassembled, Short test drive gave the impression that the engine was freer revving and the OBC mpg was definitely up, looking like previous mpg had been restored. Longer drive will confirm.

I am surprised the valve had a fair degree of soot build up. I use Shell nitro and do not incur much town driving. Also surprised - if indeed it was the EGR that was the root cause - that even a moderate build up of soot within the valve may be the cause such a drop off in mpg. As I say, ports were not blocked and the valve appeared free to move. It was in no way absolutely clogged up.  My only theory is that the valve MAY have been sticking and causing unwanted backpressure, but I cannot be certain of that.

I guess the answer is to understand that regular maintenance of the valve is required - or at least clean it out again if mpg drops off. Fortunately it is a simple job. 

 

[Deserter]

I've a;ways noticed an increase in my fuel consumption come winter, in all my diesel cars.

My 2ltr. Rav4 usually returns 47MPG on the work run but has been displaying 44mpg for the last few weeks.

[Chris1972]

I have same problem. My 2.2d4d has dropped by approx 4mpg noticed it last mth.  Car has just been serviced and still the same, I'm putting it down to winter mths as it takes longer to get warm. 

[IanML]

I have noticed this over many years with a variety of cars - 3 to 4 mpg worse in winter.

It makes sense when you think of increased use of rear window and mirror heaters, aircon to clear mist, wipers for the extra rain, lights because of earlier dusk and later dawn....