Wrong Fluid in the AdBlue Tank: What to Do Next
Owning a diesel · Published
Filled the wrong tank by mistake? Stop, do not start the engine and read this first. Acting quickly can save a lot of money.
In short
- If you have put the wrong fluid in either tank, do not start the engine and do not drive.
- Wrong fluid in the AdBlue tank can damage the pump, heater, sensors and injector.
- Draining and flushing the system quickly often avoids the need for new parts.
- Tell your insurer, and keep the receipt and a photo of the filler as evidence.
Why this mistake happens so often
The AdBlue filler is usually a blue cap close to the diesel flap, or even under the same flap. In a rush, on a dark forecourt, it is easy to pick up the wrong nozzle or the wrong bottle.
It can also happen at home. A bottle of screenwash or water poured into the wrong hole is a common story. It is a simple slip, and it is fixable if you act quickly.
First rule: do not start it and do not drive
The most important step is the simplest one. If you realise straight away, leave the engine off. Do not switch the ignition on if you can avoid it.
Turning the key on can wake the AdBlue pump, which may start pulling the wrong liquid through the system. Running the engine does the same with fuel. The longer it circulates, the more parts it reaches.
If you have already driven and a warning has appeared, pull over safely and switch off. Then call for help rather than carrying on to see what happens.
Which wrong fluid went where
The risk depends on what was added and which tank it went into.
Diesel in the AdBlue tank
Diesel does not mix with AdBlue and it attacks the seals and plastics in the pump and lines. It can also foul the sensors and block the injector.
Water in the AdBlue tank
Water thins the fluid, so the strength is wrong. A small amount may only trigger a quality warning, but the system will not clean the exhaust properly. It also leaves the quality sensor reading badly.
Screenwash or coolant in the AdBlue tank
These contain alcohols, glycol and dyes that do not belong in an SCR system. They can damage the heater, the pump and the sensors, so they should be drained as soon as possible.
AdBlue in the diesel tank
This one is a fuel system problem, not an SCR problem. AdBlue is water-based and can harm the fuel pump and injectors. Do not start the engine. The fuel tank and lines need draining by a specialist.
Why it matters: what can be damaged
An SCR system is built around one specific fluid. Every part that touches it is designed for that fluid and nothing else.
The pump moves the liquid and can be damaged by a fluid it was not made for. The heater, which stops the system freezing in winter, can be harmed by chemicals. The level and quality sensors can be coated or ruined. The injector can block or seize.
Left alone, a cheap mistake can turn into a big repair. Caught early, the cost is often only the drain and flush.
Draining and flushing the system
The usual repair is to drain the tank completely, flush the lines and pump with the correct fluid and refill with fresh AdBlue. The aim is to clear everything before it does lasting harm.
After that, the system is tested to confirm it dosing correctly and that no related faults are stored. Any warning or countdown is then cleared with the proper equipment.
What may need replacing
If the wrong fluid sat in the system for long, parts can be damaged. That can mean the pump, the quality sensor, a NOx sensor, the injector or in bad cases the tank unit. We check each one and only replace what has failed.
Typical part prices
A tank is £795, an injector is £750 and a NOx sensor job starts from £249. Labour is quoted after diagnosis, and the price is fixed before we start.
Insurance tip and how to prevent it
Check your policy and tell your insurer early. Some policies cover misfuelling and some do not, so ask rather than assume. Keep the receipt, take photos of the filler and write down what was added and when.
To prevent a repeat, buy AdBlue only in clearly marked containers that meet ISO 22241. Check the cap colour before pouring. Fill the AdBlue tank in daylight where you can. Tell anyone else who drives or fills the vehicle which cap is which.
When to call us
Bolt Remaps has been fixing AdBlue faults since 2019, and we are IMI affiliated. We come to you at home, at work or at the roadside, so you do not need to risk starting the engine. We answer calls from 6am to 9pm, seven days a week, including bank holidays.
We drain, flush and test the AdBlue system, then agree a fixed price with you after diagnosis. Work starts from £249, there is no fix no fee on the agreed outcome and a written warranty comes with it. Call 0203 038 8555.
Common questions
What happens if I put diesel in the AdBlue tank?
Diesel can damage the pump seals, the lines, the sensors and the injector. Do not start the engine. The tank and system should be drained and flushed before anything is run.
Can I put water in the AdBlue tank?
No. Water dilutes the fluid, so the strength is wrong and the system cannot clean the exhaust properly. Only use fluid that meets ISO 22241.
What if I put AdBlue in the diesel tank?
Do not start the engine. AdBlue can damage the fuel pump and injectors. The fuel tank and lines need to be drained by a specialist before the vehicle is run.
Is it safe to drive if I only added a little wrong fluid?
It is not worth the risk. Even a small amount can reach the pump and sensors. Leave it switched off and get advice first.
Will my insurance cover wrong fluid in the tank?
It depends on the policy. Some cover misfuelling and some do not, so contact your insurer early and keep your receipt and photos.
Can you come to me if the vehicle is stuck on a forecourt?
Yes, and please do not try to start it first. In most cases the tank can be drained and flushed where the vehicle sits. Phone 0203 038 8555, open 6am to 9pm every day.