Been working for next at heywood today, and they are trialing one of the volvo units on an mpg test. Whats different about this, is that the unit is running with its fuel tank never more than half full. The idea is that if it is carrying less weight, it should return better mpg. The idea behind this, is that the units never use more than half a tank at max during any run. The next time i go in (excuse the pun) i will ask to how its doing.
Hmm …calibrating ‘how much is half’ is hardly practical.
Why not spec smaller tanks from the off, not least to save lumbering the extra metal around …unless it’s only a half-hearted bit of ‘I wonder if’ type research.
The specific gravity of diesel is between 820-950 Kg/cu.m. temperature dependant.
Which in laymans terms means roughly every litre in the tank weighs 0.9 of a kilo.
so 1000ltrs on the wagon is around 900kgs.
Might be something in it if you’re ‘tankering’ fuel around if you don’t need it.
It’s only going to be a worthwhile exercise if the loads are the same weight each time - what are the chances of that!
What if the NEXT sale is on everything is REDUCED by 50 %…
So, assuming it’s a 1000l tank and a fully loaded artic at 44t MGW, that will save, at the instant the tank is full, roughly 0.2% of the total vehicle mass, dropping as the fuel is emptied. Assuming (that word again) the vehicle engine is 100% efficient, that’s less than a £3 saving per tank. Been awake 18 hours, but I think I did that right…
Cynical? Yeah.
an exercise in futility…they will have the drivers dieting next. 
The actual fuel saving per truck may not be much but there is another aspect:
If you have 500 trucks and each one has 200 litres of fuel more than it needs then thats 100,000 litres of fuel.
A litre of diesel weighs about 0.75k so thats 75,000k - equivalent to driving 4 empty trucks around for no reason.