AdBlue in the Diesel Tank? What to Do (and How to Prevent It)

Putting AdBlue in the diesel tank is one of the most common refuelling mistakes on fleets and farms, and one of the most expensive. The two fluids often sit side by side at the depot, the caps look similar on some vehicles, and a tired driver at the end of a shift only has to grab the wrong nozzle once.

The good news is that the damage is usually avoidable if the vehicle is not started. This guide covers what happens, what to do straight away, and how to set up your site so it does not happen again.

What happens when AdBlue gets into diesel

AdBlue is a solution of high-purity urea in deionised water, made to the ISO 22241 standard. It does not mix with diesel. Because it is heavier, it sinks to the bottom of the tank, which is exactly where the fuel pickup sits.

If the engine is run, the AdBlue is drawn into the fuel system. Urea and water are corrosive to fuel system parts and can crystallise as they dry out. The parts most at risk are the ones that cost the most to replace:

• the low and high pressure fuel pumps
• the injectors
• fuel lines and filters
• on some vehicles, the tank sender and in-tank pump

A tank that has been filled but never started is a cleaning job. A fuel system that has had AdBlue pumped through it can be a repair bill running well into the thousands.

What to do straight away

1. Do not start the engine. On many vehicles, even turning the ignition on primes the fuel pump, so leave the key out.
2. Stop filling and note how much went in. Your mechanic or dealer will want to know roughly how many litres of AdBlue are in the tank.
3. Call your dealer, mechanic or roadside assistance. The tank needs draining and flushing, and the filters should be replaced. Some manufacturers have a set procedure for this, so follow their advice.
4. Do not try to dilute it. Topping up with diesel does not fix it. The AdBlue stays at the bottom of the tank.
5. If the engine has already been run, stop it as soon as it is safe and have it recovered rather than driven. The less it runs, the less damage is done.

Getting the fluid back out of a fuel tank is a job for someone with the right equipment, and the drained mix needs disposing of properly. Do not tip it down a drain or onto the ground.

The reverse mistake is just as bad

Diesel in the AdBlue tank causes its own problems. Even small amounts of hydrocarbon contamination can damage the SCR system that AdBlue feeds, including the dosing pump, injector and catalyst. The same rule applies: do not run the vehicle, and get the AdBlue system drained and checked.

How to stop it happening on your site

Most misfuelling comes down to how the refuelling point is laid out. A few changes make it much harder to get wrong:

• Separate the dispensers clearly. Keep diesel and AdBlue nozzles physically apart, not hanging on the same post.
• Colour code everything. AdBlue equipment is conventionally blue. Make the hoses, nozzles, signs and tank labels consistent.
• Use the right nozzle sizes. AdBlue nozzles are smaller than diesel nozzles and are designed to fit the AdBlue filler neck. Avoid adapters or generic nozzles that defeat that.
• Use dedicated equipment. Never share drums, funnels or jerry cans between AdBlue and fuel. Cross-contamination ruins AdBlue as surely as misfuelling ruins diesel.
• Train and remind. New drivers, contractors and hire operators are the most likely to make the mistake. A clear sign at the bowser costs very little.

If you are setting up or upgrading a depot, a combined installation designed from the start is the simplest answer. Our diesel and AdBlue dual solutions and multi-compartment diesel and AdBlue tanks keep the two fluids in isolated compartments with separate, clearly marked dispensing, laid out for the way vehicles actually move through the site.

Store your AdBlue properly too

Misfuelling is not the only way AdBlue causes trouble. Poor storage lets it degrade or become contaminated, which can trigger SCR faults and derates. Our AdBlue storage tanks are built for ISO 22241 purity, with temperature control and purity monitoring available.

Talk to us about your refuelling setup

If misfuelling has happened on your site, or you want to make sure it does not, tell us how your depot works and we will recommend a layout. Get in touch or call 1300 210 480.