DEF system problems in diesel vehicles are more common than you might think. Your vehicle's performance can take a hit from these issues, which often lead to power loss, sudden shutdowns, and warning lights. These problems can get pricey to fix if you ignore them too long, so it’s important to know the early warning signs.
In this article, we’ll take a look at the number one enemy of DEF systems: crystallisation. We'll also flag other common troubles to keep an eye out for and give you some tips to keep your diesel vehicle running smoothly.
Crystallisation: The #1 DEF system problem
White crystal deposits are the biggest problem for diesel vehicles with SCR systems. These urea crystals form throughout the DEF system when water evaporates and leaves behind solid residue that can damage your vehicle’s performance.
What causes DEF crystallisation?
DEF crystallisation happens when the water component evaporates from the fluid. Several factors contribute to this. Temperature fluctuations are the most important, since DEF starts to freeze and crystallise below -10°C and heat speeds up evaporation, leaving concentrated urea behind. Contamination is another major cause since crystal formation starts when DEF touches dirt, fuel, oil, or other substances. Using poor-quality DEF adds impurities that upset the chemical balance.
Signs your system has crystal build-up
Keep an eye out for these signs:
- Reduced power output – Your engine might enter “limp mode,” limiting your speed
- Decreased fuel efficiency – Crystal-clogged injectors make your system use more DEF and diesel
- Visible white deposits – Check exhaust pipes and DEF injectors for crystallisation
How to clean and prevent crystal deposits
System cleaners are a great way to get rid of existing crystal deposits. Warm soapy water works well on mild crystallisation on external surfaces, and vinegar solution helps break down tough deposits.
You can prevent future crystallisation by storing DEF properly between -11°C and 25°C in sealed containers away from sunlight. Only use high-quality DEF that meets standards, and never mix DEF with other fluids or use dirty equipment.
Other frequent DEF system problems
DEF problems can always go beyond just crystallisation issues, substantially affecting your vehicle’s performance.
Contamination
DEF quality suffers from even the smallest contamination. Aussie conditions often mean dusty farms and mine sites, and even half a tablespoon of dirt can make hundreds of litres unusable. Metals like copper, zinc and aluminium break down when they come in contact with DEF, meaning stainless steel is the only safe material for containers.
Temperature Control
DEF freezes at -11°C, but returns to normal without any quality loss. While rare in most parts of Australia, temperatures do drop in the colder southern states. A more common problem in Australia is the risk of high temperatures. DEF stored in bulk tanks in some parts of WA, NT, and QLD can hit temperatures over 40°C, causing rapid degradation.
DEF added to diesel tank by mistake
Working while tired or a simple lapses in judgment happen, but this dangerous mistake leads to:
- Immediate metal component corrosion
- Crystallised deposits blocking philtres
- Engine misfires and power loss
- Possible devastating engine damage
Don’t start the engine if this happens. Call the professionals at KS Mobile Diesel Service right away to drain and flush the system.
Best practises to avoid DEF system issues
Good maintenance will protect you from DEF system failures that can get pricey. These guidelines will help maintain system integrity and extend component life.
Store DEF between -11°C and 25°C
The quality of DEF depends heavily on temperature control. Keep it away from direct sunlight, and make sure the temperature stays between -11°C and 25°C. The shelf life drops to about six months when temperatures exceed 30°C, but the right storage conditions can extend shelf life beyond 12 months.
Use dedicated equipment
Your equipment should never mix DEF with other fluids. Even tiny amounts of contamination can harm SCR systems. Stick to stainless steel or plastic containers, and clean your equipment with distilled or de-ionised water after use.
Check DEF levels regularly
Check DEF levels often, and top up during refuelling to keep levels right. Remember to allow for freeze expansion in cold weather, and reduce idle time to prevent crystallisation and other buildup.
Train operators on proper DEF handling
Good training prevents expensive mistakes. Make equipment inspections part of the routine, and make sure your operators know the right handling procedures, temperature requirements, and contamination risks.
Let KS Diesel take care of your DEF system
DEF system problems can quickly turn into big headaches, and they can hit your wallet hard. New parts often cost thousands, and system failures can keep your vehicle parked for weeks. Regular inspections and proper maintenance can save you from an expensive repair.
But even with careful maintenance, DEF system issues sometimes need expert help. With a fleet of fully equipped mobile diesel service trucks, KS Diesel can get to you wherever you’re parked up around Caboolture and Brisbane. We’ll use the latest diagnostic tools to find any issues and fix them fast, so you can get back on the road sooner.
Call the KS Diesel crew and tell us how we can improve your DEF system.
Frequently Asked Questions
Crystallisation is the most common DEF system issue, causing clogs in injectors, pipes, and pumps, which can lead to reduced engine performance and increased emissions.
Look out for warning lights, fault codes, reduced power output, decreased fuel efficiency, and visible white deposits around exhaust components.
Yes, DEF degrades if left out in the sun. Heat and direct sunlight can drastically shorten shelf life, so it’s important to store in a cool area out of direct sunlight.