[sepp]

after falling onto a forum thread about someone asking the FE of a certain pickup, i was intrigued by someones answer. this person claimed to get 8.5 l/100km on his diesel pickup by driving at what i took for insane RPM's. he said he was just following the manual instructions about the ideal speed to shift to each gear, and that gave him his best FE.

so i jumped on my constructor manual and found the instructions for my 2.5 l turbodiesel nissan pickup. it mentions the numbers are for ideal fuel efficiency and power.
roughly:
1st to 2nd at 20 km/h
2nd to 3rd at 40 km/h
3rd to 4th at 60 km/h
4th to 5th at 70 km/h

i tried this for some time now and it means i need to shift when im between 2500 and 3000 rpm! this way i pick up the next gear at 2000 rpm.

this is basically how i normally drive on flat terrain:
1st to 2nd at 10 km/h
2nd to 3rd at 20 km/h
3rd to 4th at 30 km/h
4th to 5th at 40 km/h

my question is that could it be that i get better FE by following the constructor instructions? at those RPM you have a much higher efficiency. because im basically always driving in 5th and the pickup can perfectly take it, but it does react slower wich means it wastes a large part of the fuel when accelerating. so wich method causes you to waste the least fuel?

-driving always in highest possible gear, but being inefficient when accelerating?

-accelerating in the lowest gear possible and operating the engine in its optimal range, but using more fuel for the high rpm?

i found that i tend to accelerate slower than before when shifting at almost 3000 rpm, wich is good i suppose. its' because the engine has alot more torque it reacts instantly to you foot. wich i suppose means that the engine is more efficient. when accelerating in 5th at low rpm, the car can keep accelerating for like 5 seconds after i stopped pushing in the pedal deeper, wich means it's wasting fuel.