Carrying out basic maintenance and regular safety checks will help keep your car in good condition and could save you money on costly repairs. Here’s a guide to easy DIY checks for the average motorist.
Motoring
Why your diesel ute or SUV is blowing black smoke
Black smoke blowing from the exhaust of your diesel ute or SUV is a warning sign that the engine may require attention, but it might not be catastrophic. Here’s what you need to do.
Despite the rise of battery-electric and petrol-electric hybrid powertrains, diesel remains the fuel type of choice for the vast majority of Australian ute and large SUV buyers today.
Valued for their strong pulling power at low revs and good fuel economy, diesel engines are often considered more capable and reliable than petrol for tough operating conditions such as towing a caravan or driving across rugged 4x4 off-road terrain. However, the heavy demands can lead to problems – and blowing black smoke at engine start-up or when accelerating is a sure sign that something’s not right.
Here’s a guide to what black smoke from a diesel means, the common causes, checks you can make and action you should take to help extend your engine’s life, reduce emissions and save on fuel.
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In this article
Oil level and air filter checks are recommened if your diesel ute or SUV is blowing black smoke, but seek professional advice for a proper diagnosis.
What does black smoke from a diesel mean?
In a diesel engine, fuel is injected into each cylinder’s combustion chamber and ignited by the high temperatures achieved when the gas is compressed by the piston. Black smoke emitted from the tailpipe usually indicates that the fuel isn’t burning completely.
As RACV Digital Motoring Editor Andrea Matthews explains, this could be due to various issues, including too much fuel in the cylinder, not enough air, or a combination of both.
“Incomplete combustion could come down to something as simple as a dirty air filter or more complex mechanical issues,” she says. “Most importantly, it’s a warning sign that shouldn’t be ignored.”
More: Australia’s best utes of 2025
Common causes of black smoke in diesel cars
There can be a number of reasons why diesel engines blow black smoke, explains RACV Regional Manager Automotive Services Philip Mack.
“These include faulty injectors, engine timing, faulty turbo, faulty rings or valves, as well as other conditions,” he says.
“Some diesels can also get blocked diesel particular filters (DPF) if they are only driven around town at lower speeds. Late-model diesels need to be driven at high speeds periodically so the system can ‘burn off’ foreign particles in these filters. If this is not done the DPF can block, causing breakdowns and more serious engine problems.”
As well as DPF blockages, common causes of black smoke in diesel cars include:
- Blocked air filter – your engine needs a steady supply of clean air to operate efficiently, so a clogged or dirty air filter can restrict airflow, causing excess fuel to burn and release black smoke via the exhaust pipe.
- Turbocharger issues – a failing or underperforming turbocharger can reduce air intake into the combustion chamber, leading to more fuel than the engine can efficiently burn.
- Boost leaks – leaks in other air induction components such as hoses, pipes or the intercooler could also impact the supply of pressurised air into the combustion chamber.
- Faulty fuel injectors – if the engine’s fuel injectors are clogged or malfunctioning, they can spray too much fuel and create an overly rich mixture in the combustion chamber that doesn’t burn completely.
- Engine wear and tear – worn-out components like piston rings and valves can lead to poor compression in the combustion chamber.
A qualified mechanic can use diagnostic scan tools to check for faulty fuel injectors, which could be contributing to black smoke from the exhaust.
Easy checks to make if you notice black smoke
The common causes of black smoke we’ve listed above can sometimes be identified by simple checks you can make around the vehicle. These can point the way to where the problem lies and reinforce the need for a qualified mechanic to properly diagnose and address the problem. They include:
- Inspect the air filter – refer to your vehicle owner’s manual for information on how to locate the air filter housing and how to open it to check its condition. If it’s dirty, clogged or damaged, it could be restricting airflow into the engine and should be replaced.
- Check your engine oil level – if the level is low, it could indicate worn engine components such as piston rings and cylinder liners that can allow oil to leak into the combustion chamber, mixing with the fuel to create black smoke. High oil consumption should be a major prompt to seek professional help.
- Watch out for warning lights – modern vehicles often display error codes for engine-related problems. If you notice a warning symbol, code or message, it’s important to get a proper diagnosis.
- Look at the exhaust smoke – if the smoke is constant and thick when the engine is revved, this points to fuel-related issues and should be attended to as soon as possible.
“These are all warning signs that should encourage you to get your diesel ute or SUV booked in to an accredited service centre,” says Matthews. “Ignoring black smoke or other factors that might be related such as a drop in power or an unusual smell from under the bonnet could cause long-term damage to your engine.”
Under a heavy load, a diesel engine could possibly inject more fuel than it can completely burn, leading to black smoke. Image: Matt Harvey
How to keep your diesel ute or SUV running smoothly
Getting a professional diagnostic test of your diesel engine should identify why the vehicle’s blowing black smoke and what needs to be done to fix the problem. Your nearest RACV Accredited Auto Care Centre should be able to help. This will hopefully save you money in the long run by having the issue resolved before it gets worse.
Once you’re up and running smoothly again, follow these tips to help avoid the black smoke returning:
- Always follow your vehicle’s servicing schedule – routine servicing intervals are based on a set time period and kilometres travelled (whichever comes first) and following these should help keep your diesel engine in top condition.
- Consider more frequent services – if your vehicle is often driven in adverse conditions, for extended towing, technical off-road driving or long periods of gravel or dusty conditions, consider servicing more frequently to keep it in optimum condition.
- Use quality diesel fuel – poor quality diesel can potentially impact combustion efficiency, so keep tabs on where you regularly source your fuel.
- Watch your driving habits – constant stop-start driving, making only very short trips, using heavy acceleration or towing excessive loads might all place stress on the engine and trigger black smoke, even in well-maintained diesel utes and SUVs. Taking some higher-speed runs periodically with the vehicle unladen is recommended.
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