OVER the years, the staff at Fleet Van have tested a number of fuel-saving devices – and one thing we can say with certainty is that most of them don’t work.

Remember those magnets you tied round the fuel pipe to make all the petrol molecules all go the same way? Or who could forget that little widget you poked into the fuel tank to ‘condition’ the petrol inside.

Both were a complete con, but you’d be amazed at how many fleet chiefs who should have known better were taken in at the time. So when Mercedes-Benz LCV specialist Simon Wood called me the other week eulogising about the firm’s motor start-stop (MSS) device, which is available as a £175 (ex-VAT) option on Sprinter and can apparently save up to 10% on fuel in congested areas, I was a little sceptical.

MSS has been available on Sprinter for some time now but strangely, the firm doesn’t seem to have done a very good job of marketing it so far.

The system works simply by switching the engine off when the vehicle isn’t moving and switching it back on again when it’s time to start again.

MSS won’t make a scrap of difference to a van hammering up and down the M6 all day, but for urban delivery fleets, Mercedes reckons it’s a winner.

I asked Wood: ‘It’s all very well to claim 10% fuel savings but can you actually prove it?’ The Fleet Van gauntlet was thrown down and the man from Merc was pretty quick to pick it up.

We arranged to meet in London, where he would provide two fully-fuelled Sprinters – one with MSS and one without – and we would ply the crowded streets of the capital in convoy before topping up again and checking the difference in fuel consumption.

Here’s how we fared...

The challenge

IT is 8am on a damp January morning and Simon Wood is looking anxious. The vans are all ready to go and the traffic in London is at its peak. The only thing missing is yours truly and photographer James Scorey. We, meanwhile, are stuck in a huge traffic jam on the A1M. Curses.

By the time we arrive and have checked that both vans are full to the brim with diesel, all the rush-hour traffic has disappeared and the roads near the Mercedes dealership in Welham Green are almost empty. Double curses. I choose the Sprinter with the stop-start mechanism while Wood climbs aboard the standard van, together with my trusty snapper.

Both are 313 CDI medium wheelbase, medium roof 129bhp models, loaded with 500kg weights in the back.

We cruise down the Holloway Road but there’s hardly a vehicle in sight. We must be the only drivers in London actually looking for congestion. Weird.

We had planned to skirt around the congestion charging zone but in desperation we cough up £16 and enter Ken Livingstone’s hallowed kingdom. As if by magic, as we approach the Barbican, we are pitched into a transportational hell.

Cabs by the hundred jostle for position, buses whizz past our vans with millimetres to spare and van drivers make it their job to park up and deposit their loads in the most awkward places possible. That’s more like it.

Again and again we are forced to halt and as Wood’s van in front chugs away in neutral, my MSS system cuts in and out as if by magic.

A quick dab on the clutch when the traffic in front starts moving and I’m off again. Easy.

Nelson’s Column looms and the traffic reaches gridlock. So much for claims of less congestion since the introduction of the congestion charge – whatever must it have been like before?

As we sit amid the chaos, seemingly wedged in forever, I imagine Wood grinning to himself in the van ahead. He must have used half a gallon just sitting there, I muse to myself.

We eventually free ourselves and head for Blackfriars Bridge and the London Eye, where our snapper intends to stop for a photoshoot.

Here, we become embroiled in a coach bonanza, while kamikaze foreigners with cameras rush across the streets after looking left and right – the wrong way. Once again, my MSS system comes into its own.

After the photos are completed, we swap vans to make sure that our different driving styles don’t affect the figures and head back through the city, along Holloway Road and back to Welham Green.

At the fuel station I expect Wood to be a tad nervous. After all, his company’s reputation rests on what happens in the next few minutes. But he looks calm and confident.

The vans show that we have covered just 24.8 miles in three hours. We fill the standard Sprinter first, making sure that the fuel comes right up to the brim. Some 2.96 litres are swallowed up.

Back at the MSS van, Wood puts his hand over the pump display just to tease me. A grin spreads across his face as he reveals the amazing truth – 1.69 litres.

Back in the canteen of the dealership, we get out the calculators and even Wood can’t believe the figures we come up with. He phones Mercedes HQ to check that we haven’t made a mistake.

But it’s true – while the standard Sprinter returned 37.58 miles per gallon, the MSS clocked up a staggering 67.02 mpg – a 78% improvement in fuel consumption.

That means a stop-start van driving 30,000 miles per year would save £4,500 in fuel over three years against its standard counterpart.

Impressive? We’re astounded.