High Fuel Consumption on the highway

I'm new to the forum and had a bit of a search around but couldn't find anyone else mentioning this.

I have a 2011 Manual Diesel 420 Highline. My fuel consumption around town is outstanding at about 8L/100km, but on the highway at a steady 110 km/h it is significantly higher and usually around 11L/100km.

I've checked tyre pressures, wheel alignment and using an OBDII plug Fuel Rail Pressure, Boost Pressure and Coolant Temp. The coolant temp was struggling to get to 75C even on a hot day, so i thought this might be the problem. Mammoth job to change the thermostat and now runs bang on 90C but the highway fuel economy hasn't improved.

I'm suspecting the DPI filter may be nearing the end of its life at 230000 kms but haven't had any error codes or warning lights.

Has anyone else come across this problem?

Comments

  • deanp100deanp100 Member

    It a nutshell no. Logic says it should be the opposite. Mine goes to 8 or so on the highway at 110. I am at 330000 kms and have had a dpf light come on once . A session of very high rpm highway driving cleared it , never to return. It make no sense to use more at 110.

  • i Agree... but it’s happening and I’ve never come across it on any other vehicle. I can’t find anything that’s obviously wrong and there’s no error codes suggesting a problem.

    Someone must have come across it before... but possibly not in an Amarok

  • PROBLEM UPDATE

    It looks like the previous owner has had the ECU remapped for more boost and more fuel between 95 and 120 kph. I found a receipt amongst the paperwork that came with the car. Stated before and after torque figures.

    If it's just a chip piggy backing the ECU rather than an actual remap, can anyone tell me where the ECU is located so I can check.

    Also after anyone who has had to get their ECU reset from a dealer and what it would cost?

  • stu9stu9 Member

    Definitely you are not alone! I can get ours down to high sixes around town, but the highway consumption is MUCH higher. Fitting different tyres made a huge difference, in the negative direction. Our on paper fuel consumption went up around 20% when we changed the original highway terrain 245/65R17 to all terrain 245/75R17. Even if you factor in the 6% increase in diameter, the increase in fuel consumption is still substantial. We have Toyo Open Country AT2 tyres. I have seen other people comment that these tyres have caused the vehicle to use noticeably more fuel. In almost every other respect the tyres have been very good. They are durable, tough and surprisingly quiet on the road. Off road traction is also surprising.

    Our tyres are near end of life, so I am planning to change them to a different brand, and go out to 265/70R17. The reason for the increase in width is multifold. I originally kept the width the same as I suspected the larger diameter tyre would cause an increase in fuel consumption, but not to the extent that we experienced. I also did not factor in the larger voids in the tread design of all terrains over highway terrains, so discovered a reduction in braking traction. This is not good. Hopefully, going to 265 width will alleviate the loss of rubber on the road with the more aggressive tread design. In addition, my brother in law has a Rok with 265 width tyres of almost the same diameter (only about 1- 2mm larger diameter). His has several times now gone through places with less stress than ours did, even though I had slightly lower pressures.

    I suspect the autos may be affected more than the manuals when fitting bigger tyres. This is only supposition because I have seen a number of owners of manuals respond to similar threads saying they still get good fuel economy with the larger tyres.

  • I'm on the standard Highway tyres 255/60R18 but have a larger set along with a 40mm suspension lift waiting in the shed... but i don't want much worse fuel economy, so it's still sitting there until I can sort this out.


    The problem is the lack of consistency.... Yesterday I did a 400 km round trip highway run from Bunbury to Perth. On the way there I averaged 8.6 L/100km. Parked for several hours and then returned averaging 11.1 L/100km. It's a flat coastal run. There was no headwind and I was actually taking it easier on the pedal coming home. The 8.6 is unusual for me on the highway, but it has happened on several occasions. If I'm keeping it under 100 kph, the economy is usually consistent at around 8.0 L/100kms, but at the usual 110 kph, thats where all the inconsistency happens

    Question 1: Could I be getting the better economy after a DPF burn?

    Question 2: Has anyone done an EGR and DPF delete with PPD Performance in Myaree

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