D40 better fuel economy

[canny lad]

I drive 100Klms a day to and from work.95 of it on the highway.
Using my scanguage I get 10.4 litres per hundred, sitting at 110-120kph.
For the past two days I have done this with the Overdrive OFF.
RPM increased to 3000 and fuel economy dropped to 9.6 kph

D40 07 Navara Outlaw

 

[joe2006]

That is quite interesting.

Do you have a bigger wheel/tyre combination than standard?

 

[jay185]

my 2010 d40 4x2 AT consumes 7.2km / liter

 

[jay185]

and i dont even rev up to more than 2500rpm

 

[Old.Tony]

I was watching my Torque application on my phone and paying attention to the fuel rail pressure, and noticed that there's a whole mess of fuel going in at over 2000rpm. Climb past 2500rpm and it's like opening a floodgate. I'll have to map the rail pressures and see what they are for certain rev ranges, then hit some flat country and do it again, so it can indicate the pressures at different speeds etc.

Suffice to say, the higher the rpm, the higher the rail pressure = more fuel being squeezed in, so I find it surprising that your economy is better by dropping overdrive.

However, I do like to try things now and again, so next time I'm out and about, I'll do the overdrive off trick and ask the ECU to show me the fuel consumption rate.

 

[KraftyPg]

OD off, higher revs and better economy, somehow I think there is more at play than just that to get better economy, if that was all there was too it Dunnydoor drivers Aus wide would be getting 2 litres per hundred.

I agree with Tony, higher revs = more juice pumped in and the difference between 2000RPM and 3000 RPM has to be substantial.

 

[joe2006]

I notice when towing the van with our diesel Pajero that I use considerably more fuel leaving it in overdrive than locking out of overdrive.

When going through a town & will put it back in drive & let the transmission do what it wants. Sometimes I forget it's in drive when I get back onto the open road. When I eventually remember, & without moving the position of my foot on the accelerator, I take it out of overdrive & my speed increases.

So with the accelerator in the same physical position, my speed (& of course revs) increases when I take it out of overdrive. I also know I use less fuel. The difference is I am dragging around 2.5+ ton & the taller gearing obviously does not suit under those circumstances.

I have not towed enough with the Navara to make a comparison.

Thats my bit for what it is worth

 

[joe2006]

After towing the van a fair bit now with the Navara, I see it is a waste of effort & fuel keeping it out of overdrive.

On anything but flat country, it is chopping & changing between gears anyway & there is a fair bit of torque converter slip even when it is in 4th. Overall it just makes for an uncomfortable journey.

I suppose it's just a matter of "horses for courses". What suits one vehicle make/model, does not neccessarily suit another.

 

[Old.Tony]

Thanks for bringing this thread back up, Joe. I forgot about it completely.

I did fire up the ECU's "LPHK" indicator and drive around with overdrive on and with it off.

Without overdrive, the car uses considerably more fuel and the fuel rail pressures are higher. The only time it's an advantage to not have overdrive on is approaching a hill - and then you can just tap the accelerator and it kicks back anyway.

So in my car at least, NOT using overdrive uses extra fuel. Getting the car up to a speed where the torque converter will lock seems to be important because it drops the revs, drops the wasted revs, lowers the fuel rail pressure and the apparent consumption (which all makes sense).

As you say, Joe - each to their own. For my driving style, overdrive suits me fine.