A truck fleet waiting to start the day with engines idling gets overlooked against the backdrop of a cumulative cost penalty that can be easily calculated. And it’s not just idling truck engines destroying the bottom line, it’s the whole fleet – bakkies, cars, tractors, and reefer truck engines.

Get everyone with a vehicle under their control to understand that excessive engine idle time is wasteful. How is fuel waste calculated in litres and then Rands/cents? A conservative guideline is 10% of engine displacement per hour equals litres burnt in an idling diesel engine.

  • A typical modern 4 X 2 distribution heavy truck with gross vehicle mass (GVM) ranging from 12,000kg to 16,000kg and equipped with a 7,8 litre turbo-intercooled Euro II engine can easily idle for one hour in a day. This would mean 0,78 litres/day and on a 275 working year will total 215 litres @ R19 per litre for a cash loss of R4085 – this has a multiplying effect with fleet size. A 100-vehicle fleet means an annual profit drawdown of R408,500.
  • Engine size impacts idling thirst. A 15-litre engine drinks 1,5 litre per hour at idle so one hour/day/275 day-year/R19 per litre totals a loss of R7838 per annum – on a 100-vehicle fleet this is an R783,800 loss.
  • This is all dependent on a diesel engine idle speed of 650rpm. Many diesel engines have idle speed adjusters and speeding up idling rpm increases consumption beyond the 10% benchmark.
  • Reputable diesel engine manufacturers estimate every hour spent on idle time in a long-haul operation can decrease fuel efficiency by 1%
  • Badly maintained trailers idle away fuel

    Stop examining the truck tractor alone for fuel consumption improvements. Start investigating trailer efficiencies. Air leaks on trailer reservoirs and brake lines are very prevalent, resulting in the tractor unit wasting fuel in firstly charging the air-brake system and then left idling all day to ensure the system remains charged.

    Look at coupling procedures. Coupling truck tractors to trailers should not be a lengthy process – what’s getting in the way of ‘couple-and-go’? Is it the terrain, in-adjustable trailer supports or any other reason for excessive idling during coupling manoeuvres?

    Driver ‘comfort’ increases idle consumption

    Stop drivers from idling engines to maintain in-cab temperatures. When it’s sub-zero and a dark, cold winter’s morning one can hardly blame truck drivers for starting and idling engines to keep the cab warm. And then idle-for-comfort again when waiting in a distribution point drop-off queue - can a business afford this behaviour?

    This not only applies to cab heating but air-conditioning as well. Most modern trucks include air-con as standard equipment and the temptation to wait in a mid-summer queue with air-con operating is just too much to avoid.

    Note that it’s illegal to allow an engine to run when a vehicle is left unattended or while the fuel tank is being filled – Regulations 308 (1) (l) and 308 (1) (n)

    ‘Weak’ batteries raise engine idling

    A rash of flat battery jump-starting will be accompanied by excessive engine idling. The fear of not being able to restart on the road leads to keeping engines running.

    Fleet audits reveal many cases of abnormally corroded battery terminals. The knock-on effect is jump-starting leading to idling engines and increased operating costs.

    Heavy traffic distorts idle-fuel consumption figures

    Scheduling a truck into peak, idling traffic is so very unproductive. Rather leave prior to and return before traffic peak and use fuel for payload at a higher average speed.

    Idling shortens engine oil drain intervals

    Failure analysis expert, Patrick Swan, comments that “Engines work best at normal operating temperature. As the temperature drops, combustion becomes less efficient, causing both higher fuel consumption and fuel dilution of the engine lubricant. As the diesel fuel that ends up in the lubricant is too thin to lubricate an engine correctly, so a cold running engine, either through excessive idling or because it is overcooled, wears faster than an engine operating at correct running temperature”.


    The USA Environmental Protection Agency (EPA) states that behavioural change is the simplest route. Transport managers must get out there early to observe engine start-up procedures and what is happening at consignees during unloading. Another powerful tool in changing driver behaviour is offering financial incentives to reduce idling. Education and driver incentives provide a partial solution to deter idling and play an important role in behavioural change.

    Petrol and diesel fuel prices make engine idling a focus area in managing fuel consumption. Simply instituting a company policy to not idle has not proven effective in changing behaviour and company policy is not going to stop a driver or machine operator from idling in extreme weather conditions.