The concept of a diesel hybrid makes sense on the surface. Diesel-fueled cars already have better fuel economy than cars fueled by regular gasoline ‒ so it would only make sense to further improve their fuel mileage by combining them an electric motor.
Is there a diesel hybrid? Yes, there is a diesel hybrid. There are multiple diesel hybrids, actually. Some notable examples include the VW Golf TDI hybrid, the Mercedes-Benz S-Class hybrid, the Citroën C-Métisse, and the Peugeot 308.
What Is a Diesel Hybrid?
A diesel hybrid is a vehicle powered by both a diesel engine and an electric motor.
If you have a series diesel hybrid, the diesel engine charges the electric motor’s batteries while the motor is what actually moves the car. If you have a parallel diesel hybrid, the wheels can be moved by either the diesel engine or the electric motor. Parallel hybrids are the most popular type of hybrid vehicle, and most diesel hybrids operate in this way.
When compared to gasoline-fueled hybrids, diesel hybrids are more durable, provide more fuel efficiency, and produce more torque. Given these advantages, it might seem surprising that there aren’t more diesel hybrids available.
However, you need to account for some of the problems that also come with diesel engines: they cost more than gas-powered engines, they’re significantly louder, and they don’t play as nicely with colder weather.
We’ll discuss the obstacles in the way of diesel hybrid popularity in a bit. For now, let’s take a look at some of the most notable diesel hybrid cars currently in existence.
Diesel Hybrid Examples
VW Golf TDI Hybrid
The VW Golf TDI Hybrid is a concept car unveiled at the 2018 Vienna Motor Symposium. It’s equipped with an electric motor to get the car moving from a stopped position and a three-cylinder diesel engine that engages when the car starts moving at higher speeds. The diesel engine is capable of producing 74 horsepower and 132 lb-ft of torque, while the electric motor maxes out at 27 horsepower and 103 lb-ft of torque.
The VW Golf TDI hybrid is a smaller vehicle designed to maximize fuel economy and interior cabin comfort. While VW has made TDi hybrid vehicles in the past, the new four-cylinder engine in this model has been optimized to decrease emissions in every part of the driving cycle.
While the diesel/electric combination VW is testing in this car certainly has potential, this particular vehicle probably won’t move beyond the concept car stage. VW has already stated that the increased cost of building a diesel hybrid means they’ll probably be going in the direction of supercharged and turbocharged gasoline hybrids.
Mercedes-Benz S-Class Hybrid
Mercedes-Benz also made a diesel hybrid concept car. In 2007, the company unveiled the S300 BlueTEC diesel hybrid. The four-door luxury vehicle is capable of hitting more than 40 mpg. Like the VW Golf, the electric motor exists to get the car moving and help with acceleration, while the 2.2-liter diesel motor handles most of the actual driving. This thing is powerful too ‒ it produces an impressive 224 horsepower and 413 lb-ft of torque.
The S300 diesel hybrid actually made it to market with a 2014 release. The $106,000 base price was pretty hefty, but Mercedes-Benz still saw limited success with it this vehicle.
While the S-Class diesel hybrid is no longer in production, Mercedes-Benz is planning on releasing diesel hybrid versions of cars in their C-Class and E-Class lines ‒ so be on the lookout for that.
One of the first ‒ and the most interesting ‒ diesel hybrid concept cars came from a French car company by the name of Citroën. During the 2006 Paris Motor Show, they released the C-Métisse: a bright red four-door diesel hybrid coupe.
One of the most novel aspects of the C-Métisse is its engine setup. Twin electric motors are placed in the back of the car to operate the rear wheels, while a 2.7-liter diesel engine drives the front wheels. It’s pretty darn powerful too ‒ the V6 diesel engine gets about 208 horsepower, while the electric motors produce about 295 lb-ft of torque each.
While the car never made it to market, that apparently was never Citroën’s plan. The company stated they merely wanted to prove that a diesel hybrid car could produce the same level of power and performance as a regular gasoline-powered car or diesel-powered car. They definitely succeeded in that regard ‒ and going by the sleek exterior and fire-red paint job, they did it in style.
Peugeot 308 Hybrid HDi
Rounding out this list of diesel hybrids is the Peugeot 308 Hybrid HDi hatchback. Introduced at the Frankfurt Motor Show in 2007, this car represents Peugeot’s second rendition of a diesel hybrid vehicle ‒ the first being the 307 Hybrid HDi, which was first introduced in 2006.
The 308 Hybrid HDi sports a 1.6-liter HDi engine to handle most of the driving, and an electric motor to assist in startup and acceleration. At 83 mpg, this car is incredibly efficient. The Toyota Prius, which is often used as a benchmark for hybrid vehicle fuel efficiency, is 25% less fuel-efficient than Peugeot’s latest diesel hybrid.
The 308 Hybrid HDi is quite environmentally friendly as well. It emits 38% less CO2 than equivalent HDi models, and it’s 15% cleaner than the Prius.
Does a Diesel Hybrid Make Sense?
If you’ve done any research into diesel hybrids, you’ve probably noticed that there aren’t many of them available. Most car manufacturers have either stuck to tried-and-true gasoline-fueled hybrids or gone all-out to create completely electric vehicles. Many of the diesel hybrids I mentioned at the beginning of this article are only prototypes, which means manufacturers are only just starting to experiment with diesel hybrid technology.
There are a couple of reasons companies have shied away from making diesel hybrids.
The first is cost. Car companies like to make vehicles that people can afford. Selling diesel hybrids makes that harder to do, as the diesel versions and hybrid versions of cars are significantly more expensive than the base gasoline models. Take the VW Jetta TDI: the diesel model costs about $5,000 more than the gasoline model. The 2019 Honda Accord tells a similar story, with the hybrid model costing about $2,500 more than the base model.
The second reason is also related to profits. The California Air Resources Board (CARB) is the “clean air agency” of California, and some lucrative vehicle markets use CARB guidelines to determine what kind of vehicles can be sold. CARB guidelines make it extremely difficult to sell diesel vehicles in large markets like New York and California, so car companies have been hesitant to invest in diesel products when more profitable alternatives exist.
That isn’t to say diesel hybrids don’t make sense though. One of the main benefits of a diesel engine is the enormous amount of torque it provides. This has led to cities using diesel hybrid technology in larger vehicles like buses. San Francisco, for example, started using diesel hybrid buses all the way back in 2007. The city was concerned about excessive emissions from their public transport vehicles, but a gasoline-fueled hybrid wouldn’t have been able to run their buses. So they invested in diesel hybrid technology, and have been using it ever since.
The jury is out on whether these diesel hybrids were actually a smart purchase. For starters, a diesel hybrid bus costs several hundred thousand dollars more than a traditional bus. The fuel savings over the bus lifetimes would have to be incredibly good to justify that kind of increased cost ‒ and it’s not really clear whether they are.
In Seattle, another city using diesel hybrid buses, their public transportation website states that fuel efficiency on their buses is 4 mpg ‒ which is much better than the 2.6 mpg traditional buses get. However, there is some debate over whether this 4 mpg number is accurate, with some detractors claiming that the diesel hybrid bus mpg is actually less than that of conventional buses.
I know you came to this article looking for information on diesel hybrid cars. I’m talking about buses at the moment because they’re one of the only examples of diesel hybrids seeing any kind of mass use in the real world. The insights gained from looking at diesel hybrid buses ‒ like the questionable improvement in fuel efficiency ‒ can certainly be applied to diesel hybrid cars as well.
Although diesel hybrid technology has been used in public transport for over a decade now, its use in smaller vehicles has been extremely limited until quite recently. In addition to the profitability issues I mentioned earlier, diesel hybrids haven’t been all that popular because the added torque simply wasn’t needed in smaller vehicles.
Will diesel hybrids see more success in the future?
Companies like VW and Mercedes-Benz must see some future in diesel hybrid technology ‒ if they didn’t, why would they be devoting time and resources into developing diesel hybrid concepts?
It’s tough to say. The obstacles in making a commercially successful diesel hybrid vehicle are definitely higher than regular hybrid vehicles or 100% electric vehicles. The U.S. market for diesel cars is essentially dead, even if those cars are paired with an emissions-reducing electric motor. Diesel hybrid vehicles also cost significantly more to manufacture, which translates to a significantly higher purchase cost for the consumer.
That isn’t to say it will never make sense though. Gasoline prices are expected to rise in the coming years, which will make alternative fuel sources even more attractive than normal. Although diesel fuel is also expected to rise in price, so gasoline users interested in cheaper fuel sources probably won’t turn to a diesel fuel hybrid. Consumers looking to make the switch to an energy-efficient and environmentally-friendly vehicle may decide to skip the hybrid completely and go for a 100% electric vehicle. This is something that will only become more likely as electric charging stations continue to pop up in gas stations, parking lots, and other highly trafficked areas.
I don’t know what these car companies are planning ‒ this new round of diesel hybrid concept cars might exist purely for research purposes for all I know. However, I wouldn’t be shocked to see more diesel hybrid cars on the road in the coming years ‒ especially in diesel-friendly locations like Europe.