Why has my fuel economy improved

[solmanic]

Let me preface this thread with I'M NOT COMPLAINING, but I sure am curious...

The last two tank fulls in my Puma Defender have managed substantially greater mileage than any previous ones.

Since new the Defender has averaged 600-620km from a tank (approx 62l-65l each fill). Pretty much bang on 10l/100km or a bit over, every tank, city, highway or off-road. The vehicle has now done 27000km and the last two fill-ups have gotten 680km and 702km with 62-64l put in. This last one I ran it until the low fuel warning light came on just to check that it still worked. I thought the calibration might have gone out, but no - light came on, and the tank wasn't any emptier than before.

Now I always expected the economy to improve as the engine loosened up, but not all of a sudden. I thought the tank before last might have been an anomaly but this last one was the same. It appears I have had an overnight improvement of about 1l/100km. I haven't, to my knowledge, changed my driving style or been driving anywhere different and the vehicle has not had anything heavy taken off. Both the last fills were at the same Caltex-Woolworths service station I usually use.

Has Caltex changed their Diesel somehow?
Is my extra 8c per litre here in Queensland buying me better fuel?
Is there a magic setting in new Defenders that changes the engine tune to something more efficient at 26000km?
Is it my imagination?
Has a Holy man secretly given my Defender a blessing whilst it was parked at the shops?
Should I just shrug and say "oh well, that's Land Rovers for you" and go on my merry way?

[TimNZ]

Probably just better fuel?? I've found the fuel economy improved after about the first 15000k's, its done 40000k's now. The other week I repeted a 500k(ish) trip I did when I first brought my car, it nearly used a tank the first time, (fuel light came on), but this time I had quarter of a tank left.

Tim

[JamesH]

Trying to find a negative spin on what appears to be simple good fortune happens to be specialist area of mine...

Sometimes fuel pumps can be cantankerous and click off at different levels, the guage might show full but the actual level might easily be a litre less in the filler pipe. I don't know about yours but my guage takes a while to mover while the car drinks the "extra bit".

Sure, this sort of anomally generally evens out when you do your next fill and you have already had your next fill so you would have expected a correction but maybe the pumps have been serviced (or need a service) and delivering the fuel differently. You might get your correction on the next fill?

[DeeJay]

Kinda reminds me of the film where a guy kept skiting to his neighbour, (played by Robin Williams), about his Volkswagons great economy, so Williams kept putting extra fuel in it each night until this guy got 125mpg and was going nuts trying to keep calm about it..

Got a locking fuel cap ??

[Richard]

you been using BP diesel? found ive been getting better fuel economy with my defender as well using that, theres some additive they have been advertising they add to their diesel

[solmanic]

Nope. All recent fills have been at our local Woolworths Caltex.

[Mrlandyman100]

My last tank full was at BP i just worked out and maybe thats the reason why i seem to be getting better km/l. But i will find out tomorrow when i fill up again. I think i have gone about 30-40km more when at the same point on the fuel gauge.

[omvanders]

My landie-nut mechanic swears that Caltex gets him up to 10% better economy than 2 other brands in particular, one of which starts with B and the other with S. I'm yet to be convinced, but am in the throes of testing his theory.

[Scallops]

I have known many people who will tell you that any engine will get it's best fuel economy from about 30000km onward - why? I don't know. Mine did this too - I went to about 9l per 100km.

[vnx205]

Kinda reminds me of the film where a guy kept skiting to his neighbour, (played by Robin Williams), about his Volkswagons great economy, so Williams kept putting extra fuel in it each night until this guy got 125mpg and was going nuts trying to keep calm about it..

Got a locking fuel cap ??

That was a classic.

Unless your tank is a lot easier to fill than mine on my cab/chassis, it is unbelievably easy to get significant apparent fluctuations in fuel economy.

After the nozzle clicks off and froth dribbles out on the ground and the tank appears to be full, I can add another five or six litres, provided I have the patience to dribble it in very slowly.

So that means I could leave the servo with only 70 litres. That would mean that the last tankful would appear to have been about 10% better than normal and if I filled up really carefully, the next one would appear 10% worse.

So the difficulty of filling some tanks, especially with frothy diesel, can give an apparent 20% variation in economy from one tank to the next.

I tend to be a bit cynical about fuel consumption claims based on one tank or even just a few tanks full.

That doesn't mean yours isn't real or isn't accurate, but I bet the circumstance I have described is more common that dramatic changes in economy.