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Hybrids vs. Diesels: Which is Better?

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From Brian Sy, Featured Contributor
Posted on May 27, 2008

Exploring the two most popular gasoline alternatives.

With fuel economy and the environment suddenly on everyone's mind, the world's automakers have been taking every measure to help cars conserve. Lots of little tweaks have been made, but our only real hope of seriously reducing consumption lies in a more drastic change: finding something other than gas to make our cars go.

For the near future, achieving that end will depend on two means: diesels and gas-electric hybrids. No doubt you've heard of others. There's natural gas, which is hanging on for dear life, and hydrogen, which is too costly and unstable to be viable anytime soon. And who can forget E85 ethanol, the miracle fuel that cuts mileage by 30% and wastes the nation's food supply. The list goes on, but if we narrow it down by common sense, yeah, the world of alternative fuels is pretty much a dichotomy for now.

So, which one's better? That depends on what you look for in a car and what you hope to achieve by switching. Let's break it down by a few key areas.

Mileage

How much gas will you save? Hybrids and diesels pretty much give the same answer: one-third. As in, for any given car, switching to a hybrid or diesel will result in a miles-per-gallon bump of 33% (give or take 10%) compared to a gas engine of similar size.

With diesels, you can mostly take that number at face value. Diesels are simply more efficient than gas engines overall, owing to super-high compression ratios and the 18% higher energy density of the fuel. As a rule, they drink less at any speed or when performing any given task. For example, a 2008 Mercedes E350 gets an estimated 17 MPG in the city and 24 on the highway, while the similar diesel-powered E320 bumps that up to 23 and 32.

Hybrids, by contrast, save more fuel the slower you go. Whenever you're stopped, the engine promptly shuts off, leaving the fuel supply untouched while all the poor saps around you are getting exactly zero MPG. In low-speed driving (the most wasteful kind), the electric half of the powertrain does most of the work, and up to 40 MPH or so, it still helps out at least occasionally. Not surprisingly, hybrids are the high-mileage champions of the metro grind.

It's different out on the freeway. First, there isn't a single hybrid with a strong enough battery to maintain high speeds for long. Even if there were, remember that the secret to hybrids is their regenerative brakes – the source of their free electricity – and there isn't much braking action going on in steady-state cruising. Sorry bub, but no braking means no free juice. In this instance, hybrids act just like any other gas-powered car, so diesels win.

Bottom line: city dwellers should stick to hybrids, while victims of long, costly commutes will find solace in diesels. Everyone else will want to weigh the remaining factors.

Environmental Impact

This one won't be easy. There are already debates of gas vs. diesel and gas vs. hybrid, and bringing up diesel vs. hybrid just complicates things further. But let's do it anyway.

Since hybrids are so dependent on gasoline, we should start by examining the gas vs. diesel part. Well, here's the fun way to sum up the situation: buy a gas car if you want to melt the planet; buy a diesel if you want to screw up the air and give everyone cancer. Got that?

Ok, let's elaborate a little. Diesel engines use up less of the world's resources and generate fewer hydrocarbons, carbon monoxide, and carbon dioxide (CO2), the big bad mofo of global warming. The fuel itself also takes less energy to refine. On the other hand, diesels are guilty of spewing out more oxides of nitrogen (NOx) and particulate emissions – or in more casual terms, smog and soot. Smog is nearly synonymous with air pollution and asthma problems; soot is where cancer comes in.

Unfortunately, picking your favorite method of death has never been a clear-cut decision. American environmentalists have been dissing diesels for ages (they've generally been banned from new cars in California since 2000, and in the northeast for almost as long), yet half the European continent has always embraced them with open arms. Blurring things further is diesel's recent jump on the fast track to cleanliness. A great milestone came in October 2006 when the first batch of gas stations started America's four-year transition to low-sulfur diesel fuel -- which, by allowing more aggressive filters to be used can supposedly cut smog in half and soot by 90%. Impressive.

In 2007, Mercedes spearheaded the new school of diesels with its BlueTec engines, but other improvements remain in the future. Diesel returns to Volkswagen cars in 2009 (the Jetta's up first), and Honda, Nissan, Subaru, and GM supposedly jump in shortly thereafter.

Now, moving on to hybrids. The general opinion is that compared to pure gas cars, their net effect is positive. After all, driving a 44 MPG Toyota Prius around for 120,000 miles (ten years) means 1,411 fewer gallons of gas have to be sucked from the ground compared to covering the same miles in a 29 MPG Toyota Corolla, with the only drawback being a [recyclable] dead battery at the end of the journey, plus the energy that went into manufacturing it. On the opposing side, one study claimed a Prius actually does more damage than a Hummer, but more intelligent scientists quickly came forth to expose that "study" for what it really was: a load of &#!@ with grossly manipulated data, and a publicity stunt (the Hummer was assumed, unjustly, to have double the lifespan).

So, if hybrids are friendlier than gas and gas is friendlier than diesels (if you want to take the American viewpoint, that is), it's reasonable to say that hybrids beat diesels. But again, we should wait a couple years and see what comes of this low-sulfur stuff before passing judgment.

The Driving Experience

Here's where things get subjective. Hybrids and diesels feel noticeably different from gas cars and from each other, but when it comes to the desirability of those differences, all opinions are up for grabs.

To the uninitiated, both would feel weird. Hybrids' culprit for weirdness lies in the fact that so many key systems have been electrified. Their electric steering tends to feel lighter, more artificial, and less connected. Their electric regenerative brakes can send strange signals up through your leg as they work, and also whenever they make the transition to the real brakes. Additional awkwardness shows up under acceleration, as battery power frequently hands off to gas power and back again. On the upside, people enjoy hybrids' absolute silence at idle (when the engine turns off).

With diesels, "weird" has traditionally been the nicest possible euphemism for unpleasant, disgusting, putrid, etc. Surely, those of you actually old enough to remember the 80s are familiar with terms like diesel rattle, diesel smoke, diesel stink, and diesel sluggishness. However, as tragic as it is, the 80s are no longer with us, and those stereotypes are about as relevant as Cyndi Lauper and Wham! Diesels still rattle a little, but they've cleaned up to the point of the smoke and smell being nearly nonexistent, and their acceleration now ranks right up there with other cars, thanks to the universality of turbochargers, common-rail fuel injection, and better engineering.

In fact, some people swear by cars being more fun to drive with diesel engines. The biggest reason is their monstrous load of torque, and the feeling of brute force that goes with it (even though there's little impact on actual acceleration times). Diesels also add less weight to cars than do hybrid powertrains. And some people just like the way they sound and feel. Call it character. Call it an acquired taste.

Overall, you could probably say that the average American driver would get more of a kick from diesels than hybrids. Diesels have a simple, rugged appeal and, through their torque, satisfy the fundamental American craving for instant gratification. Still, the high satisfaction ratings reported by owners in both camps would imply that plenty of people could get used to -- maybe even learn to love -- the idiosyncrasies of either one.

The Economics

You hear the question all the time: how many miles till I get my money back? It's the question that nearly made diesels extinct in the mid-80s when the answer became too high a number, and it's a question hybrid haters use today as propaganda.

With hybrids, the answer is at least more predictable. Owners pay for the same gasoline as everyone else, making it just a matter of calculating the point at which the improved fuel economy pays back the initial price premium. In the beginning, that premium was pretty high. Looking at Toyota, hybrid capital, the Prius's has been around $3,000 (vs. a theoretical non-hybrid Prius), which would take the better part of a decade to earn back. However, the premium for the newer Camry Hybrid is closer to $1,000 after adjusting for equipment, which cuts down the payback time considerably. If gassing up a normal 24 MPG Camry costs $1,750 a year and a 32 MPG Camry Hybrid takes it down to $1,313, you get the cash back in three years, tops.

Diesels, on the other hand, use a fuel whose price follows its own path (and isn't as widely available, by the way). Sometime around 1990, diesel shot past gas and never looked back; as of this writing it's about 40 cents (12%) higher than regular-grade gas here in California. But that's still no match for our grandstanding one-third boost in mileage. Also, looking over the price sheets at Volkswagen and Mercedes, the price premium for the diesel engine is usually $1,000, which means that even when the fuel costs more, the payback never takes longer than a couple of years.

A point in hybrids' favor is the tax credits. However, they're set to expire at the end of 2010, and some manufacturers have already hit their quotas (Toyota) or are fast approaching them (Honda) so new buyers of these makes won't be eligible.

A point in the favor of both diesels and hybrids has been outstanding resale value. A four-year-old Volkswagen Jetta GLS TDI is worth over $5,000 more than its gas equivalent, and a same-age Prius holds a similar advantage over a Corolla. But it should be noted that as hybrids and diesels become more common, and as diesel cars regain legal status in the coastal states in 2009, resale value could lose some of its luster on both sides.

It's a close race allright, with lower price premiums (diesels) facing off against tax credits and cheaper fuel (hybrids); notice that all three factors are in constant flux. However, there is one constant: life expectancy. Diesel engines have a reputation of lasting forever, thanks to their less violent internal operations and more robust construction. Hybrids, on the other hand, need to be taken in every 150,000 miles or so to replace a battery that will cost $1,000 a few years from now, at last estimate. To the minority of you who plan to keep your car until the wheels fall off, consider this the tiebreaker.

Parting Thoughts

Putting it all together now, we have 1. a tie, 2. a slight, uncertain win for one side, 3. a slight, uncertain win for the other side, and 4. an advantage that will matter to almost nobody. Hey, what kind of lame cop-out comparison is this?

The answer is: a complicated one, and a changing one. Still, for the moment, strengths of hybrids and diesels touch upon different themes, with less pollution on one side and more driving fun and financial rewards on the other. So if you're aching for a grand generalization, try this: buy a hybrid if you're in it for the environment; go diesel if you're more in it for yourself.

Read More:

• Get Paid to Save Gas
• Improve Your Parking Etiquette
• Cars: What's in a Name?
• How to Read Car Classifieds

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Brian Sy is a featured contributor for vLane.