Diesel versus Hybrid: The battle for eco-friendly supremacy

Car buyers are faced with a multitude of choices when it comes to trying to fuel economy. High efficiency gas engines, micro-cars, diesels, hybrids, plug-in hybrids, and – of course – full-on EVs are all tempting options. Trying to choose what’s best is an imposing task, even for people who – like us – spend their entire waking lives thinking about cars.

To narrow that choice down a little bit we are going to comparing diesel and hybrid powertrains, as they are the most widely available alternatives to gas powered cars. Even better, these are both options that do not require you to trade in all your clothes for sandals and hemp ponchos. So without further ado, let’s get down to it.

Economy

If you are thinking about a hybrid or a diesel for your next car, chances are good that gas mileage matters to you. And it should, because gas prices show no sign of dropping in future. Though the wide variety of cars available with alternative powertrains make this slightly complicated; the simple answer is that diesel achieves better fuel economy on the highway, while hybrids are more efficient in town.

The reason for this has to do with how the systems operate. Diesel’s advantage is extremely efficient combustion which allows for extremely good fuel economy at freeway speeds. Hybrids on the other hand gain their advantage from recovering energy that would ordinarily be lost during starts and stops, so the less stopping you do the less you use the hybrid system.

Nonetheless, hybrids do – on average – achieve better rated mileage. Take for example two comparable midsize sedans: the Ford Fusion Hybrid rated at 47 mpg highway and city versus the Volkswagen Passat TDI rated 43 highway and 31 city. I’ll admit these numbers don’t look great for diesel, at least on paper.

That disparity, though, is partly due to the way the EPA calculates fuel economy figures. Test drivers accelerate and brake slowly, according to strict guidelines. This isn’t to suggest that EPA testing is bad, simply that the rules are ideal for the underlying technology.

In my experience, diesels – especially on the highway – outperform their stated numbers, whereas hybrids commonly under perform. And before you send me angry comments, it s not just me: real drivers showed the mileage in the Fusion Hybrid at an average of 36.8 mpg and the Volkswagen Passat at 39.5 mpg. Okay now you can send me angry comments.

But the question doesn’t stop there. Diesel presently averages around $0.50 more per gallon than regular gas. In lower-price vehicles that don’t require premium fuel, this can make a big difference.

On yet another hand, diesel cars, while more expensive than their gas counterparts, are also cheaper than hybrids. In the case of our comparison the difference is only around $500 with the VW starting at $26,675 and the Ford running $27,280, but you are also getting a much better all-round car with the Passat … sorry Ford.

If that weren’t enough, diesel has historically retained a much higher resale value than both gas and hybrids. In the end the overall difference is essentially a wash in terms of cost, with exceptions depending on the vehicle.

Technology

While each automaker is happy to tout how its technology is not only unique but also superior, there are common threads to all hybrid and diesel technologies.

Let’s start with hybrid tech. There is a key feature that sets a hybrid system apart from a normal gasoline powered car: energy regeneration. Essentially, the electric motor spins backward to collect kinetic energy that is typically wasted in braking and coasting.

Hybrids vary in some important ways though. For instance while most hybrids now use the same type of lithium ion battery packs that are used in EVs, Toyota’s Prius still comes with an old school nickel-metal hydride battery pack.

Some companies are also making use of hybrid technology in new ways. For instance, Acura is using hybrid drive to create all-wheel drive by placing electric motors to drive the car’s rear wheels.

Diesel technology is old; in fact I believe that Ramses III had a Mercedes-Benz diesel engine in his chariot. But it has advanced a lot in recent years. The introduction of common rail fuel injection revolutionized modern diesel powertrains. This system uses a single piezoelectric injector that injects fuel at stunningly high pressures  of as much as 3000 psi. This means that each detonation in the engine is more powerful and makes for much more efficient, not to mention cleaner combustion.

Performance

While cost might be a wash, performance isn’t. Hybrids have come a long way in the last decade. If you want efficiency without having to sacrifice performance and fun, diesel is still far ahead.

Early hybrids were often downright unpleasant to drive; power delivery was choppy and never there when you wanted it. They were generally very heavy cars for their size because the butt-load of batteries on board (that’s a technical term, mind you). Driving a second generation Toyota Prius was as good as carrying a sign telling people you simply didn’t care about cars.

Modern hybrids aren’t that way, thankfully. Their power comes on more smoothly and evenly. But even with the presence of electric motors, it rarely feels ‘electric’. What’s more, there are still those big, heavy batteries to carry around, which interfere with acceleration, handling, and braking. There are some exceptions, like the upcoming Acura RLX Sport Hybrid, which is likely to put a lot of gas-powered cars to shame. For the most part, though, hybrids still lag.

Diesel, on the other hand, is a different story. When we drove the Audi A7 TDI, we loved it. Not only does it drive and perform well for a diesel, with its several truck loads of torque, it out performs most gas-powered luxury cars on the road. That’s not just true at the top of the spectrum either, midrange Mercedes and BMW diesels offer stunning performance.

At this point, as a drivers’ car, I would take a diesel over a hybrid sight unseen.

Environmental impact

This is an area that might be surprising. At face value, with high gas mileage and low emissions, hybrids seem like the easy answer. But as we have previously covered at Digital Trends, vehicles with batteries may not be nearly as “green” as is often claimed.

This is a complicated issue. Essentially, batteries – particularly lithium-ion batteries – are both incredibly energy intensive and also toxic to produce. This means that the carbon footprint for hybrid production is much larger than a gasoline-only or even diesel-powered car.

In fact, according to some studies, fully electric vehicles have a bigger carbon footprint than diesel powered vehicles in areas where most electricity is produced using fossil fuels.

Modern diesel-cars should not be compared with truck engines that blast clouds of panda-killing soot into the air. Thanks to improvements in technology, current diesel cars are comparable in terms of particulate emissions to any other gasoline-powered car. In fact Volkswagen and Audi’s clean diesel technology makes cars like the Passat TDI cleaner than 93 percent of other cars on the road.

As with price, there will be specific exceptions to this rule, but diesel is greener than hybrid technology.

Conclusion

Ten years ago it the hybrid v. diesel choice would have been easy, if only because there were so few hybrids and diesels to choose from. These days shoppers are faced with a virtual cornucopia of hybrid- and diesel-powered offerings, which makes one definitive answer difficult.

Here are some takeaways: Don’t be fooled by the EPA sticker; a hybrid might get better mileage on paper, but the real-world efficiency might come as a nasty shock. If you really want to enjoy driving your car, get a diesel. If you want something cheap, think about a hybrid. Most diesels on the U.S. market come from German automakers, which means they’re cost fistfuls of Deutsch Marks. If you care about your carbon footprint, do your research. From our standpoint, though, diesel is likely to be ‘greener’ than a hybrid.

With the next generation of diesels and plug-in hybrids on the way, the answers to all these questions may change. For now, at least, I personally would choose diesel over hybrid any day of the week.

Some of our Favorite Diesels:

Some of our Favorite Hybrids:

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