Fleet operators could be in a for nasty financial shock if they fail to take account of the cost of replacing diesel exhaust fluid when calculating vehicle service, maintenance and repair budgets, according to Derwent Management Services (DMS).

Diesel exhaust fluid - which is best known to fleet operators as AdBlue, although that is a commercial trademark - is designed to treat exhaust gases and help vehicles meet stringent exhaust emissions standards.

First introduced into HGVs, a tank containing the fluid is now fitted in most light commercial vehicles and is increasingly to be found in cars.

However, automotive industry data provider DMS ssays not all car makers highlight the cost of topping up the diesel exhaust fluid tank or the cost of a ‘clean and drain’ in scheduled servicing costs.

Car and LCV diesel exhaust fluid tank capacities range between 18 and 31 litres and the fluid costs around £1.10 per litre. Typically a vehicle may need fluid levels topped up 50-100% at a service, although volume usage is linked to vehicle loading, environmental conditions and driving style with the smoother the style the longer the liquid will last.

Steve Chambers, DMS research director, said: "Topping-up the diesel exhaust fluid tank could cost at least £20 per company car or van per service once labour charges have been applied. But most motor manufacturers are not highlighting either the cost of the fluid, additional labour or the tank capacity in their published SMR calculations.

"In many cases, fleet managers only discover the additional cost when the vehicle has been serviced and it is highlighted on the related bill."

With the typical company car undergoing perhaps three services during its fleet life that could amount to, at a conservative estimate, £60 per vehicle having to be added to a fleet SMR’s budget.

Chambers added: "In many cases it is a hidden cost for fleet managers and therefore an unbudgeted one. On a 100-vehicle fleet with each model undergoing three services the additional SMR cost could amount to £6,000 and possibly more.

"Cost management is the number one issue facing all fleet decision-makers and we believe that manufacturers should clearly signpost the cost of diesel exhaust fluid in their SMR calculations."

Among motor manufacturers, Mr Chambers singled out Mercedes-Benz, which has introduced diesel exhaust fluid on its environmentally-friendly BlueTEC models, for clearly highlighting the cost of a top-up on a model’s first service and a ‘clean and drain’ on a second service and so forth on alternative services. The cost for a diesel exhaust fluid top up on the Mercedes ML 4x4 assuming a 50% top up is £23.80 including labour and £47.65 for a drain and refill.

He said: "Although only a small number of manufacturers are currently using diesel exhaust fluid to break down polluting nitrogen oxides into harmless water vapour and nitrogen gas we anticipate that a tank will increasingly become a standard feature on models."