Fleet operators and their drivers are being stung by the frequency and cost of AdBlue top-ups, with some diesel vehicles needing a top-up every 3,000-4,000 miles.

That’s effectively every six tanks of fuel (assuming 500 miles per tank), with costs varying. A DIY approach costs around £15 but take it to a maintenance supplier and you could be looking at twice that figure. We were quoted £75-£100 by one dealer.

This is a scenario most fleets will have to face.

AdBlue is a brand name for an additive that is 32.5% urea and many manufacturers are using it in their diesel powertrains to meet Euro 6 emissions regulations (all diesel cars and vans registered after September 1, 2015 have to emit a maximum of 80mg/km of NOx – less than half the previous cap – with many vehicles sold before this date already complying with this rule).

The clear liquid is injected into the selective catalyst reduction (SCR) system in the exhaust chain, where it triggers a chemical reaction which converts NOx into nitrogen and water vapour. It has already been used for a number of years in commercial vehicles, but is something fleet managers and car drivers may not have experienced until a warning light comes on signalling a top-up is needed.

Therefore, it is important that drivers are aware of the process so it doesn't come as a shock. If the warning light is ignored and the AdBlue runs out, the vehicle stops and will not restart until it is replenished. When this happens will depend on the car and how it has been driven.

Peter Jardine, group fleet manager of Countrywide, has a number of Audi A6 Ultras on his fleet and has found that drivers are having to get the AdBlue tank topped up every 3,000 to 4,000 miles – at the company's expense.

"When we first spoke to manufacturers about AdBlue, they suggested top-ups would just be done when the cars were serviced, so we decided not to charge drivers," he says. "We're now having to order vehicles with bigger AdBlue tanks."

Peugeot and Citroën say their vehicles will require a top-up every 12,500 miles (fitting with the service interval of some, but not all, models), while some Vauxhall and Volkswagen vehicles could require refilling every 3,000 miles.

Consumption will also vary from car to car. Mike Cooke, fleet operations manager at fleet management firm FleetEurope, says: “You could have two identical cars with identical mileages but, while one might be used over a long distance once or twice a day, the other may be completing numerous short journeys. The total distance could be comparable, but AdBlue usage will differ massively."

Jardine has agreed a rate of £32.50 per fill with his maintenance provider. "If we fill up 13 times per contract, this is a cost of £422 per car," he says.

Another issue is deciding on who pays for the top-ups. Russell Adams, commercial vehicle engineer at Lex Autolease, suggests a relatively simple solution.

“We consider AdBlue a consumable, similar to fuel," he says. "As such, the onus is on the operator of the vehicle to ensure it is adequately topped up and cover any costs incurred."

However, Simon Pilcher, supplier manager at LeasePlan, adds: “If the service schedule states the fluid needs to be completely changed, we will take care of it," he adds.

While it is now becoming accepted that the additive is not included as a service, maintenance and repair (SMR) expense covered by a leasing company, it remains unclear whether a fleet operator should cover the cost or pass it on to the driver.

Fleets have a number of options when it comes to sourcing AdBlue. The first, and potentially most costly, is to use the dealer network. Costs vary considerably, with some brands having a fixed price policy, either for a full top-up or per litre. Peugeot and Citroën offer a top-up of up to 10 litres for £9.99, while BMW charges £24.99. Volkswagen, Audi and Seat are among those charging on a per-litre basis, with a fixed price of £1.50 per litre. Outside these fixed price policies, for other brands the results are likely to be similar.

Jaguar Land Rover vehicles on a service plan receive a free top-up but, for those outside a service plan, prices are "at retailers' discretion so may vary”.

Vincent St Claire, commercial director of service management company Fleet Assist, which manages SMR networks for leasing companies including Alphabet, Ogilvie and Pendragon, says dealer charges are a minefield.

"The big issue is managing the costs from the garage,” he says. “The AdBlue fluid can be purchased in bulk for as little as 30p per litre but we are seeing garages charge anything up to £15 per litre and 30 minutes' labour to top up the tank."

The company is negotiating terms with garages and plans to offer a fixed price top-up for clients.

The second option is for a driver to obtain a refill kit from a dealer's parts department. The majority of brands offer a 1.89-litre refill container, which has a special valve to make filling up easier. Costing between £6 and £8, it's not the cheapest way to fill up, and several containers may be required for a full top-up, but it is straightforward.

The practical process of a driver refilling AdBlue varies significantly depending on the type of container, and the location of the filler on the vehicle. Models that have been designed with AdBlue in mind, such as the new Audi A4 and Volkswagen Passat, will often locate this under the fuel filler flap on the side of the car. Others – where the tank has been added to the vehicle midway through its life, including many Citroëns, Peugeots, and the Volkswagen Tiguan (see long-term test, page 72) – will locate the filler cap under the boot floor.

The special refill containers offered by dealers click into place, meaning there is no spillage. The 10-litre capacity containers available from motor factors, some dealers and many petrol stations, are perhaps one of the cheapest ways for a car driver to top-up, but are not without their issues.

In cars where the filler cap is located in the boot floor, a funnel may be required to reduce the risk of spillage. The containers are supplied with a tube, but these may not be long enough for easy refilling.

The 10-litre containers cost between £10 and £18, and should be large enough to reduce the frequency of top-ups.

Some fleet managers are wary about allowing drivers to top-up the additive themselves. "I won't go down the DIY route," Jardine says. " My drivers would be putting it in the fuel tank or washer bottle – you name it."

Fleet managers can enable or disable the ability to pay for the additive on their fuel cards, with Allstar and BP among those offering the functionality.

Drivers may be tempted to use the considerable number of AdBlue pumps available at motorway filling stations, but Paul Norman, manager at chemical company Air1, explains that the pumps cannot be used for passenger cars. “Cars will have onboard AdBlue tanks a fraction of the size of a truck’s and the pump flow rate would result in overfilling in a matter of seconds,” he says.

Cooke adds: “It is worth pointing out buying in bulk as a consumer is not advised. AdBlue is a bio-product and therefore has a use-by date. Keeping a quantity in the garage or boot of the car may seem like better value, but just as you wouldn’t drink out of date milk, you shouldn’t use AdBlue past its use by."

Setting your fleet's AdBlue policy

1. Identify the vehicles on your fleet that require AdBlue

Many Euro 6 diesel vehicles require AdBlue top-ups, but in many cases it won't immediately be apparent. Ensuring you and your drivers know which  vehicles require the additive eliminates surprises.

2. Decide who pays for AdBlue top-ups

The majority of leasing companies don't include AdBlue in maintenance  policies. Ensure your drivers are aware they are responsible for payment if you decide this should be the case.

3. Suggest a recommended refilling process

Particularly if your company is covering the cost of top-ups, it is essential your drivers understand your policy for refilling to avoid excessive charges. They need to know if they should take the car to a dealer and recharge the cost to the business, pay for it on their fuel card, or submit it for payment as a business expense.

If drivers are to pay themselves, ensure AdBlue fill-ups are disabled on their fuel card system.

AdBlue models, range, and dealer top-up costs

Brand	Audi	BMW	Jaguar Land Rover	Mercedes-Benz	Peugeot Citroën	Volkswagen	Vauxhall
Affected models	All Euro 6 diesels excluding A1, A3 and TT	5 Series, 7 Series, X5, X6	All Euro 6 diesels	Most Euro 6 diesels, excluding A-Class	All Euro 6 diesels	Most Euro 6 diesels excluding Polo, Golf, Beetle, Scirocco	Zafira Tourer/Insignia 2.0-litre Auto
Estimated range	n/a	9,000 miles	5,000 – 17,000 miles	9,000 – 17,000 miles	12,500 miles	3,000 – 7,000 miles	3,000 – 7,000 miles
Dealer top-up price outside scheduled service	£1.50 per litre	Fixed charge of £24.99	Included in JLR service plans between services	Top-up before first service free, then free labour	Fixed charge of £9.99	£1.50 per litre	Prices vary for AdBlue, but free labour for fleets