The Parade: How Does AdBlue End Up in a Diesel Tank, and How Do You Avoid It?

Why does AdBlue in a diesel motor need its own filler?

Many modern diesels on the roads around The Parade and The Mount carry two liquids, not one. Diesel goes to your motor. The exhaust, not your motor, is where AdBlue ends up: dosed into the gas to fresh them, from its own tank.

Each tank has its own filler. Under one flap, side by side: that is the layout on many motors. Elsewhere, AdBlue's filler sits beneath the bonnet or in your boot instead. Topping up your diesel side at the petrol pump goes on constantly. Rarely topped up, AdBlue normally goes in out of a bottle, tipped by a driver who must stop and think what cap to use. The slip lives in that gap.

The AdBlue filler and your diesel filler: telling them apart

Before you tip anything, whether on a drive in Woodley or a forecourt around The Parade, check these. They take a few seconds.

• Colour and marking: an AdBlue cap is commonly blue, or says "AdBlue", where a diesel cap usually does not. Go by the cap, not where it sits.
• Plenty of motors fit AdBlue the smaller filler of the two.
• Open the filler flap and check for a label — plenty of vehicles mark what goes in each inlet right there.
• The handbook. If the filler isn't by the diesel cap, it's in the boot or under the bonnet, and the handbook says which.
• Ask the person who drove it last — before you leave, not when the light comes on — when you collect a hire or company car from somewhere like the car park at Earley.

What happens when our engineers get there in The Parade

The van reaches the car wherever it has come to rest — your own drive, near Whiteknights Indoor Bowling Club, or by Aldryngton Primary School. Both the work and the price depend on three answers — what liquid, what quantity, and whether it's run — so our technicians ask. That price is given over the phone, before any van leaves.

Next: a drain, then a thorough flush of the whole system. With AdBlue that matters more than with petrol: it crystallises and is corrosive to some of the metals in a fuel system, so it does not wash out on its own. Testing comes at the end: before that, clean diesel goes in, and the filter is flushed or replaced as needed. The motor is fired up next and tested to be sure it runs correctly, all before we leave.

Using pumps fine on a working forecourt and quiet enough for use outside a house at night, most jobs where the motor has not run take about half an hour once our engineers are there. Your insurer usually wants the engineer's report and your VAT invoice, and both are yours once the job is done. Payment comes on the day, with no deposit. Plenty of insurance policies include misfuelling cover, and so it's worth checking yours while we are on the way.