Fuel woes - Is it worth keeping?

[Bundacliff]

I have read with interest the many pages about fuel economy on the D40 engine. I too have a recently purchased 2008 KC diesel and am not impresses with 15l/100km economy on flat highway (Ceduna to Perth). With all the experiments being performed has there been a successful solution identified or should we cut our losses and move on to something different? I have had Nissan reset the fuel pump etc but no change.

look forward to your replies

bundacliff

 

[Old.Tony]

Welcome to the forum.

The Nissan Navara's fuel economy isn't all that bad, really. Given its shape - it's not very aerodynamic - and its weight of 2tonnes+, for a small diesel it does very well.

That weight doesn't do it any favours when you're taking off. I've found that as little as 500rpm extra makes a difference. I try to keep my take-off rpm to 2500 or less - I don't exactly win every race when the lights go green, but then it's not supposed to be a race, I have to keep telling myself.

Your cruise speed also has a lot to do with it. The effort required to push the vehicle through the air increases with speed - it's not a linear increase, because as air velocities and pressures change around the vehicle, the vehicle struggles more and more. The sweet spot for the D40 is right where the torque comes on - about 2,000rpm - which translates to around 95km/h.

We proved this beyond any doubt at Christmas when we towed our van to Uluru. Trying to sit on 120km/h made the thing drink mid 17s to mid 18s. Winding it back to 95km/h and taking off gently brought the consumption down to 15s and 16s. This was with a full tub and towing a 1.8T van, I guess we were sitting at around 4.5 to 4.6T all up.

Try a tankful - or even part of a tank (couple of hundred km will do) using this method:

* Don't use cruise control

* When taking off, use about 2,000rpm if possible but if it's a hill you're climbing, let it get up to 2500rpm.

* When climbing hills, don't push the thing up the hill, hold your rpm at 2500 tops, et the car slow down, people behind can just wait

* Coast downhills

* Keep your max speed to 95km/h

* If you've got an auto, as the car passes 75km/h, back off the accelerator a little and let the torque converter lock up as early as possible, then gently bring the vehicle up to cruise speed.

It might seem like "teaching grandma to suck eggs" but these are the things that I do to reduce fuel usage and they seem to work. Not towing and lightly loaded (we're about 2500Kg without anything in the tub, so guess about 2600Kg) we get mid-10s on the highway, mid-12s in the city.

 

[the_bluester]

I have to say that I reckon later ones do have an issue. I have an R51 Pathfinder, which is exactly the same in the front bodywork and if there is any aero difference it would be the minor one of having a full body and not a tub. The R51 also weighs around 2200kg so it is heavier then a D40. I do not drive it with fuel economy in mind and it regularly sees over 3500 rpm (Auto) it is about to hit 180,000km and has been averaging about 10L/100KM ever since it was new.

 

[KraftyPg]

There has been a few reports of economy that high in KC's on this forum but like Tony said it can easily come down to the driver. It appears from most reports the KC's do average higher than most DC's but there's been no logical reason for it as far as I know.

Last year when I did the Nullarbor run my economy was mid 10's and I was loaded with about 350 odd kgs on the back axle. The stretch between Ceduna and Norseman we had worse fuel economy than Norseman to Perth. Form Ceduna I was getting high 10's and from Norseman I got low 10's, I was averaging 97kph, I was running for about 3 hour stints at a time and the temps were 35 and higher. On the return I got into 9's from Perth to Norseman which is pretty good considering the towns and the hills but the strip of what many consider to be flat nothing from Norseman to Ceduna still cost me high 10's.

So the road, the weather, the wind, the driver, the load and the speed all have something to do with your economy and given that you don't elaborate much on weather conditions, your driving style and loads it's hard to really pin point any one reason why your economy can't be improved. I'd be pissed if I was getting 15's but then I don't even get 15's when I've been hooning around the paddocks.

 

[Dave]

Is it a auto ?

 

[John C]

I have a 2008 Navara duel cab ST-X Auto, did a trip from Brisbane to Lenox Head a month back and got 8.69 litres per 100 klm's, pulling the 900 kilo van I get around 12 litres per 100 klm's, around town average 10 litres per 100

 

[Bundacliff]

The vehicle is manual and during the trip to WA speed averaged 105 - 108km/h. Today was in touch with DVG Morley City (the Nissan dealer who reset the pump etc) and they (hopefully) will be getting back to my local dealer with some alternative checks to be performed. They indicated that they want to measure the output of each injector in the first instance. Currently cannot complain with the service from DVG but will see how long it lasts.

Will update on the results

Thank you for your replies

Bundacliff

 

[KraftyPg]

during the trip to WA speed averaged 105 - 108km/h.

That will be one of the big difference, going by other threads with the D40 the difference that 10kph makes is substantial and over such a long distance you'll notice it in the wallet a lot more than a lazy arse like me doing 97 on the same stretch of road.

 

[westy350]

There is something wrong with these cars I don't belive you can just blame the driver of course the driving style does have some effect on the fuel economy but I still belive there is something wrong with the cars and Nissan don't want to fix it.

 

[KraftyPg]

Well when you find the problem can you tell us all because this low to mid 10's are really killing me.

 

[d40 abuser]

im with westy after so many years making diesel engines nissan just f*#ked up its not driver error its the car ive tried to drive mine like grandpa and a little gain but f*#k all

 

[westy350]

Yep same mine is sh*t no matter what I do I have tried everything its the worst car I have ever had for fuel, Krafty maybe there is nothing wrong with yours mate but I never ever seen below 11.5L/100km and are extremely lucky to get 12.5L/100km and thats holding up traffic everywhere I go.

 

[Old.Tony]

I'll admit my fuel consumption is worse with the larger tyres. In 100,000km when I have to change these BFGs I'll go back to 255/70s.

There are other things that waste fuel, not entirely Nissan's fault - they are required to comply with emission standards and part of the method they MUST use to meet the standards is to WASTE fuel.

Stupid, I know, but that's law for you. It doesn't always make sense.

Drop your DPF and CAT, stop the injector output during the exhaust stroke, fit a catch can, vent the PCV to atmosphere, block your EGR and THEN let's see how your economy is on standard tyres. I bet it improves.