D4D Fuel consumption lower at high speed

[StuckInTheMudd]

My D4D 3.0 gets about 13.4 km/l in town. But on the open road this drops to about 11 km/l.

I thought that diesels were supposed to be more economical on the highway. Is my tuning wrong or something, or am I entirely mistaken?

[ThysdJ]

Depends on what speed you are driving at on the open road. Anything over 110/120 and there is a lot of wind resistance. Besides, 11km/l on a D4D is very good, no matter where you're driving..

[dalkill]

i get about 10km/l consistently... mixture long road and town driving.
never go over 120, and keep revs to max 2500rpm.

[StuckInTheMudd]

In town a keep at around 1000rpm.

Highway is 100-120km/h. Revs at around 2000-2200rpm at those speeds.

[Mars]

I experienced the same with mine generally speaking. But I can get similar consumption to city driving if I take it easy when cruising. I have almost never seen 11 to 12 km/l. Maybe once or twice but never 13. Mine stays constant at about 9.6 to 9.7 km/ lt. but drops if I hammer it on the open road. Mine is a 4x4 and is un-chipped and stock standard.

[StuckInTheMudd]

Mine is also a stock 4x4. Maybe being in Cape Town improves the consumption.

My main concern/curiosity is that I've heard numerous times that a diesel should be more economical on the highway. Is this true?

[jmouton]

My D4d gets about 10km/l in town. On the open road @ about 120 I get 8-9km/l. 140 about 7-8, and @160 I start getting into cruiser territory 6-6.5km/l

[StuckInTheMudd]

Why is everyone's consumption so high? Is it just because my vehicle is new? (31000km)

[Mud Dog]

Diesels develop a lot of power right from idle but as they climb the rev range that power curve drops off quite dramatically after about 2500rpm. It's therefore reasonable to believe that they are more fuel efficient at lower revs and your findings could be considered as being normal - depending on driving style of course.

Your driving style could well be a large part of the reason for your good consumption figures.

[StuckInTheMudd]

Ah. That makes sense. Thanks for the insight, that's what I wanted to know :)

[ChrisF]

There is a very good reason all manufacturers quote fuel consumption at 100km/h.

From 100 to 120km/h the wind drag effect DOUBLES, as drag is a function of the "speed squared".

For each vehicle you will find a "sweet spot", anything from 90 to 125km/h where it has its best fuel consumption.


With the RAV4 I am seeing a clear difference in fuel consumption between 115 and 125km/h .... still working on finding that magic figure inbetween the two.

with the 2,5 D-4D the sweet spot was around 105 to 110km/h - with the massive camper canopy. On a trip from PE back to Cape Town we stuck to the speed limit of 80 to 100km/h for most of the distance, got some stupidly good fuel consumption .... just tooooo slow for long trips.

[Changes]

My D4D 3.0 gets about 13.4 km/l in town. But on the open road this drops to about 11 km/l.

I thought that diesels were supposed to be more economical on the highway. Is my tuning wrong or something, or am I entirely mistaken?

13.4 km to a liter diesel in town................!!!! Don't take your vehicle for any more services, just drain the oil yourself and leave the rest as is...

[ash007]

Stuckinthemud

Are your consumption figures from the onboard computer or what you calculated at the filling station manually.

I consistently find the onboard computer over calculating with 0,8 km/l.

My true consumption manually calculated avg 11.8 km/l in town. All standard 2013 Dakar D/C 4x4 no canopy 50 000km (tyres 2.1bar original duelers).

Open road I avg 10 km/l

Sent from my SM-G360H using Tapatalk

[StuckInTheMudd]

Yes it's the onboard computer. Toyota is perhaps candy-coating their product. I'll do a manual calculation this week and see how that looks...

[Mars]

Mine is also a stock 4x4. Maybe being in Cape Town improves the consumption.

My main concern/curiosity is that I've heard numerous times that a diesel should be more economical on the highway. Is this true?

My fuel consumption has stayed constant from brand new to 282500 ks. I need to add that although I generally do not cruise at high speed on the higways ie. much over 130 I always tend to accelerate rather hard. I am certain that if I get the discipline to accelerate slower it should be better. 9.7 km/lt for such a big vehicle is good for me. I am also talking about actual consumption calculated from actual figures always filling up to automatic stop. I have a complete record of every liter of diesel I put in the bakkie since new.

[dalkill]

Maybe StuckInTheMudd getting better figures cause he has extra cab rather than doublecab due to less weight ???

[StuckInTheMudd]

Maybe StuckInTheMudd getting better figures cause he has extra cab rather than doublecab due to less weight ???

I wouldn't rule that out. I think the greatest factor is that I drive Miss Daisy

[StuckInTheMudd]

Update: Ok so my computer is lying to me. Measured my actual consumption the past week: 12.2 km/l.

Still not too bad though I guess.

[Mud Dog]

Odometers are never really accurate enough and neither do I trust those onboard computer consumption figures. Best way for meaningful data is to use GPS distances and litres at the pump.

Compare your odometer distance against your GPS distance next time you do a little longer trip - you might be lucky and find that they're pretty close, but depending on tyre size fitted they can be more than 10% out. The litres at the pump are normally very accurate - those pumps normally get re-calibrated quite regularly.

12km/lit is still pretty decent.