What Causes AdBlue to Crystallize | Insights of MPG Tuning

AdBlue is a vital fluid for reducing harmful emissions in modern diesel engines. However, many vehicle owners run into a common issue: AdBlue crystallization. At MPG Tuning, with over 19 years of experience and more than 500 five-star reviews, we’ve diagnosed and resolved countless AdBlue-related problems. In this blog, we’ll explain what causes AdBlue to crystallize, what damage it can lead to, and how to prevent it.

🚛 What Is AdBlue?

AdBlue is a non-toxic, water-based urea solution used in diesel vehicles with Selective Catalytic Reduction (SCR) systems. It helps convert nitrogen oxide (NOx) in exhaust fumes into harmless nitrogen and water vapour, drastically cutting emissions to meet Euro 6 standards.

❄️ Why Does AdBlue Crystallize?

AdBlue crystallization occurs when the fluid evaporates, leaving behind solid white urea deposits. This can happen for several reasons:

Exposure to Air When AdBlue comes into contact with air—especially if the tank cap isn’t sealed properly or fittings are loose—the water component evaporates, leaving urea behind, which hardens into crystals.
Leaks or Spills Small leaks or overfills around the AdBlue filler cap can cause the fluid to dribble and crystallize on contact with air. These crusty white deposits are common around filler necks and tanks.
Low-Quality or Contaminated AdBlue

Using cheap or contaminated AdBlue may cause unexpected crystallization inside injectors or the SCR system. Always use ISO 22241-compliant AdBlue to avoid impurities that can accelerate breakdown.

Improper Storage or Temperature Extremes
AdBlue should be stored between -11°C and 30°C. If stored incorrectly—either too hot or exposed to sunlight—the fluid can degrade, leading to crystal formation.
Incomplete Purging of Injector Lines

When the engine shuts off, some systems don't purge residual AdBlue from the injector line. This leftover fluid can crystallize inside the injector and block the AdBlue dosing system, causing performance issues or fault codes.

🔧 What Problems Can Crystallized AdBlue Cause?

Crystallization can cause serious issues if not addressed promptly:

Blocked AdBlue injectors or nozzles
Malfunctioning SCR system
Warning lights or fault codes on the dashboard
Reduced engine performance or limp mode
MOT emissions failure

These issues are often misdiagnosed by general garages—resulting in costly part replacements that don’t solve the root cause.

🛠 Expert Diagnosis from MPG Tuning

At MPG Tuning in Cannock, we’re specialists in AdBlue diagnostics and repair solutions. With nearly two decades of hands-on experience, we’ve seen every AdBlue issue imaginable—especially crystallization.

We also offer AdBlue delete services for off-road or export-only use vehicles, with full transparency and mechanical integrity always at the forefront.

✅ How to Prevent AdBlue Crystallization

Follow these expert tips to keep your AdBlue system healthy:

✔️ Always tighten your AdBlue tank cap securely
✔️ Use only high-quality, ISO-certified AdBlue
✔️ Store AdBlue in a cool, dry place
✔️ Avoid spillage during refills
✔️ Get your AdBlue system checked regularly if warning lights appear

📍 Serving Cannock, Staffordshire & Beyond

MPG Tuning is proud to be one of the most trusted names for diesel diagnostics and AdBlue solutions in the Midlands. With a solid track record of over 500 five-star reviews, customers from across Staffordshire rely on us for honest, reliable, and technically sound services.

🚗 Book Your AdBlue Diagnostic Today

If you're experiencing issues with AdBlue warning lights, poor performance, or suspect crystal buildup, don’t leave it to chance.

📞 Call MPG Tuning now

IMI Certified Tuning Specialist

MPG Tuning Ltd
Unit 44 Rumerhill Business Estate
Cannock, Staffordshire, WS11 0ET
www.mpgtuning.co.uk
www.remappingstaffordshire.co.uk

Tel: 01543 466662

MPG Tuning Offer Professional ECU Remap and Tuning services including but not limited to ECU Remapping, EGR Delete, DPF Solutions, HHO Carbon Cleaning, VAG Emissions Recall Scandal Rollback, Tricore Processor Programming, Boot Mode and Traditional Chip Tuning.

MPG Tuning is based in Cannock Staffordshire but serve customers from further afield typically from the following areas, Lichfield, Burntwood, Rugeley, Stafford, Brownhills, Walsall, Wolverhampton, Birmingham, Tamworth plus many more areas throughout the West and East Midlands.