New D-max fuel economy

Stevo - Is your D-Max fitted with a DPF? The DPF system is notorious for wrecking fuel consumption figures, simply because extra fuel is regularly injected into the engine in a post-combustion process - or injected straight into the DPF itself - to heat up the DPF, to the required 600 deg C, to burn off the accumulated soot.

The DPF dilemma

I do not own a DPF fitted vehicle, have no intention of ever buying one, and I see the DPF system as a poor pollution solution and a "quick fix" - on a par with the early "smog pumps" on the 1980's petrol engines, where an air pump was added to the engine, thus causing power losses.

Cheers, Ron.

Stevo
The 6 speed top two ratios are both an overdrive situation and the highest ratio means the engine is turning less. So much so, that the tailshaft is nearly doing twice the rotational speed of the engine, not quite but getting close. Of course it will shift out of 6th immediately the situation or load demands it, it is a cruising only gear, because the engine torque cannot hold that ratio AND drive the same load up hill of accelerate while in that gear.

The pre 2012 model only had 4speed auto with a 4th of 0.705 : 1 and a 4.1 finaldrive ratio so more revs for same road distance with same dia tyres.
The newer models have a 3.727 final drive, a bit more power and both overdrive ratios above the 4th (which is 1:1) are more higher speed ratios than the original model.

That combined with the tendancy to have bigger dia tyres makes it even more highly geared.
Therefore, it will certainly swap ratios as it's programme sees the need.
I would imagine the 6th is purely to get economy when there is very little load on the engine. ie minimal weight and flat travel. Other than that and especially when towing, manual selection within the auto, will mean the use of 5th and lower will most likely return better fuel economy. Especially when towing.

Have you got any roof bars or rack on roof of cabin or canopy? If so it will reduce economy if not faired in with a wing to make airflow gently go up and over those turbulent areas.

Stevo - All of the latest 6, 7 and 8-speed automatics are running two overdrive gears, with 4th in a 6-speed being the direct drive gear.

When you are loading up an overdrive gearset, such as pulling a heavy load up a hill, you are driving a smaller diameter gear with a larger diameter gear.

When this happens, it loads up the teeth excessively on the smaller diameter gear, with the associated higher risk of the teeth on the smaller gear stripping - as compared to the normal gearing setup, where a smaller diameter gear is driving a larger diameter gear.

Normal gearing, where a speed reduction is taking place, simply places less stress on the gear teeth.

So, the engineering principle is that you should change out of overdrive gears if you want to really start lugging with a heavy load, and thereby putting maximum torque through the gearsets.

Thus the transmission computer is set to change down early when in the overdrive gears, to keep excessive lugging load off the overdrive gearsets.

Re the canopy - yes, anything that increases your frontal profile eats into your fuel economy.
It doesn't take much increase in frontal profile to seriously increase wind resistance.

For this reason, manufacturers have been designing "slippery" shaped front ends of vehicles for quite a number of years now, as any lowering of wind resistance makes for an immediate improvement in fuel economy.

Cheers, Ron.