Do you really want to lower motoring costs?

Yeah and less stress, I drive to Brisbane from the Gold Coast each
day, leave a bit early, drive in the slow lane, on about 95ks an hour,
and watch the others go by, I carry a fair bit of equipment in the
Navara, and still get about 750 KS out of a tank of fuel.

Cheers
Daza

I tried a little experiment, a couple of weeks or so back, I drove from
Brisbane to the Gold Coast when the fuel guage showed nearly empty, I sat on 95ks per hour, and the plan was to fill up when the fuel light come on, it came on as I was pulling into our driveway,
a week later I done the same thing,when the guage showed nearly
empty, I sat on 100 to 110ks per hour and the fuel light came on
about 15ks from home, I know the story about sucking up crap from
the bottom of the tank, but I wanted to know how far one could go
on a tank of fuel, if you were desperate, when travelling.

Cheers
Daza

I drove a rental car fitted with a trip computer that gave a real time read out of the l/100km used and the most economical speed was in the highest gear somewhere between 50 and 60kph - nowhere near the ideal torque for the motor, just less wind and other resistance.

It is a myth that higher speeds are more economical in a car because you are driving at the peak of the torque curve as wind and other resistance is wrecking any savings made.

Now can someone tell me the most economical speed over a certain distance in my boat, 10mph off the plane at around 1500rpm or 15-20mph on the plane at 3000 to 3500rpm or even higher at 22 - 25mph at 3700rpm, the manufacturer's recommended cruising speed.??.

Stevesub

Well perhaps you might be able to explain why my Humvee uses less fuel travelling at 100 - 105kph than at 90 - 95.
The engine is obviously not spinning hard enough at the lower speed to be in its power/torque range.
Aerodynamics don't come into it as there isn't any!! It is shaped like a brick with a vertical windscreen.
I thought I was imagining it at first but I've repeatedly got better economy at the higher speed on the same 200km trip, regardless of direction, wind or weather. Sometimes the difference is only 1l/100k other times up to 3 or 4 l/100k.
And to top it off it is easier to drive at the higher speed as the torque converter isn't locking and unlocking repeatedly.
As a matter of interest it usually gets 15.5 - 16.5 litres per 100k at cruising speed, not bad for something that weighs around 3 tonne, 6.2 litre V8 diesel, auto and has the a aerodynamics of a brick shi*house.

My experiences that I have mentioned above are the facts that I have observed with our own vehicles and rental cars. I also know that our Troopy is considerably more economical at 90 kph than 100kph. I did a trip from MLB to BNE a couple of years ago, one tank at 90kph, one tank at 100kph with cruise control doing its job. I cannot remember the exact difference but it was in the order of 2l/100km better at the lower speed.

Like the Hummer, the Troopy is nearly 3 ton with the aerodynamics of 2 bricks including a flat windscreen but less frontal area than a Hummer.

As for your Hummer, well good on you, but I think that you will find that most vehicles are more economical at lower speeds. You may have answered your own question with the torque converter not always being locked at the lower speeds. Our Troopy and the rental car where both manuals in 5th gear on mainly flat ground so no losses with an unlocked torque converter.

The general consensus with this thread seems to be that if you slow down the more economical most peoples vehicles are with a definite improvement in fuel used over a certain distance at 90kph when compared with higher speeds.

Stevesub.

Peter and Traveller
I was not going to post my observations, as most people just politely smile and nod when I tell them that my petrol RB30 Patrol gets far better fuel consumption when the engine is revving at or over 3000 rpm.
Which is well over 100 kph.

I first noticed this 3 years ago after fitting extractors and doing all the necessary mods I have described in other posts about improving the performance of these engines (including a 40 sq inch air ram on the snorke and 40 psi in the tyres) (time to put all that info in a blog I think)

My wife (the one on the dune) took the vehicle to North Qld to see her family and spent considerably less money on fuel over the 2200klm trip than when I drove. She informed me, that She sat on between 105 and 110 all the way ( She has a Toyota Celica and drives the Patrol the same way) . I have done the same trip many times at 100kph and at night sitting on 90-100 and had 2 lit /100km worse consumption -consistently. It is an easy run to do economy figures for as each way we stop for fuel once in Rockhampton and top up at our destination so I can do the same sections at different speeds day night ULP and PULP Summer winter hence some variations in figures
Figures 90-100kph - 17-18 lit/100k never changes since bought the vehicle
105-110 15-17lit/100k
110-115 17-20lit/100
Over 120 the fuel gauge just dropped too fast to bother going there
These figures have been consistent for the last 3 years.
As traveller suggests I think in such a heavy vehicle (which is shocking on fuel at the best of times) when the engine hits its most efficient torque/power band then the engine obviously uses less fuel. Overall it sounds and feels best at this RPM - Cant explain the wind resistance factor but Im not imagining these figures.

(Oh and I was given a sample of Fuel tabs to try last year I was very scientific about trialling them - didnt find any difference in fuel consumption figures at all - Just in case anybody is wondering about them.)
Thought this may shed some more light on the comments posted above.


cheers

Kerry W
Road Conditions Coordinator