Diesel cars have more torque, record better mileage, and usually require less maintenance than gasoline vehicles. Despite all this, they still get a bad rep. They’re the less popular choice, and some people even doubt their reliability. This is likely because there are so many misconceptions surrounding diesel vehicles, including one that claims they need to be started daily to remain in good condition.
Do Diesel Cars Require Daily Running?
Ask around and you’ll more or less get the same answer from actual diesel vehicle owners: no, you don’t have to run your diesel car every day. Some owners have found no issues starting their diesel cars even after months of letting them sit in their garage.
While it’ll ultimately depend on the condition of your car, you most likely won’t run into any issues if you don’t start your diesel car every single day. This is thanks to two features you’ll find in most modern diesel vehicles.
CRDi Fuel System
Some diesel engines have a simple direct injection (DI) fuel system, which sends the fuel directly into the engine’s ignition chamber rather than into a pre-combustion chamber as on some older diesels. More modern diesel engines have a common rail direct injection (CRDi) fuel system that sends the fuel to a pressurized common rail. The common rail then sends the appropriate amount of diesel through the injector into the chamber.
The entire process results in a much smoother and more efficient combustion, better performance, and enhanced fuel efficiency. This also means CRDi engines are less likely to suffer issues from cold starts and operate smoothly even in low temperatures.
The controlled injection also reduces stress on various engine parts, prolonging engine life.
Cummins light vehicle diesel engines up to a certain year have manifold heaters, but other diesel engines have one glow plug per cylinder that provides needed heat when the weather is cold and compressing the air doesn’t raise the cylinder pressure temperature to the flash point of the diesel.
The glow plugs do not ignite the diesel fuel, natural compression does. You get 2 degrees Fahrenheit for every pound of compression and diesels generally have at least a 17:1 compression ratio. This means 400-500 psi of compression, heating the air from 800 to 1000 degrees Fahrenheit. Regulating the fuel feed is what provides acceleration on a diesel.
Cummins light vehicle diesel engines up to a certain year have manifold heaters, but other diesel engines have one glow plug per cylinder that provides needed heat when the weather is cold and compressing the air doesn’t raise the cylinder pressure temperature to the flash point of the diesel.
–Richard McCuistian, ASE Certified Master Automobile Technician
Improved Filter Head
A common issue diesel engines can run into is air entrainment, which is when tiny air bubbles get trapped in the fuel. Because diesel fuel has a higher viscosity than gasoline, the air bubbles don’t rise to the surface fast enough. They can form larger bubbles, interrupt the fuel flow, and prevent the engine from starting.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: On diesels with return lines, if the return line becomes clogged, the fuel system will “make air,” and have issues.
To prevent this, many modern vehicles use an improved filter head with an outlet line exiting directly from the top. This leaves no room for air bubbles to collect or expand, allowing them to pass through the line out of the filter as a very tiny bubble.
What Are the Benefits of Starting a Diesel Engine Often?
While it isn’t necessary to start your diesel car every day, there are some benefits to taking the extra time to do so regularly. Here are some examples:
Prolonged Battery Life
If your diesel engine won’t start after sitting in the garage for too long, it’s likely because of a drained battery. Your car uses up battery juice even when it isn’t running, and the alternator only charges the battery when your vehicle is running. This means that keeping your battery in good condition will require you to drive your car at least once a week for at least 30 minutes.
Passive DPF Regeneration
Modern diesel engines are equipped with diesel particulate filters (DPFs), which are responsible for trapping soot and ash to reduce toxic emissions. Over time, however, soot naturally builds up on the filter, causing decreased engine power and poor fuel efficiency.
By driving your diesel vehicle, you actually allow your engine to undergo a process called passive DPF regeneration. Hot exhaust gasses from your engine burn the accumulated soot, clearing the filter.
How Long Can Diesel Sit in a Tank?
It’ll depend on several factors, but in general, you can expect high-quality diesel fuel to last around six months in a fuel tank. Letting it sit for longer than that will likely cause oxidation, where hydrocarbons will start to react with oxygen in the tank. This can damage fuel lines, fuel injectors, and other engine parts that can be costly to repair. In some cases, algae and bacteria can even grow in the tank.
With proper storage and maintenance, diesel fuel can sometimes last up to 12 months or longer. Storing the fuel in high-quality fuel containers and keeping them in a cool, dry area can prevent evaporation and contamination. Using fuel additives can also help your diesel fuel last longer by fighting microbial growth and oxidation.
How Often Should You Start Your Diesel Car?
Starting your diesel car once a week or at least twice a month should suffice, but keep in mind that this is just the tip of the iceberg when it comes to maintaining your vehicle. If you want to keep driving your diesel car for a long time, be sure to follow your manufacturer’s recommended maintenance schedule.
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