By Eric Peters

Diesels and hybrid vehicles both offer 40 mpg (or better) capability in something other than an economy car package.

But which is the better choice?

The best thing about hybrids -- right now -- is the diversity of available configurations and bodystyles. There are hybrid coupes (Honda Insight) small sedans (Honda Civic hybrid) to mid-sized sedans (Toyota Prius) to sporty sedans (Honda Accord hybrid) to SUVs (Lexus Rx400h, Ford Escape hybrid). Some of these models emphasize fun-to-drive qualities, some luxury, some versatility -- but all deliver exceptional fuel economy compared to conventional vehicles in their size range.

And even more choice is on the way -- including no-compromises high-performance luxury sport sedans from Lexus (GS450h).

The worst thing about hybrids -- right now -- is that they are significantly more expensive to buy than an equivalent gasoline-only vehicle. For example, the base price of the 2005 Honda Civic hybrid is $19,900 -- while the base price of the standard Civic DX is $13,260. Similarly, a Toyota Prius will cost about $2,000-$3,000 more than a features-equivalent mid-size sedan with a conventional gasoline engine -- and so on. While there's no question that over-the-road fuel savings are substantial, it's equally true that one still has to come up with considerably more up-front money to get into a hybrid vehicle.

Also, no one really knows what down-the-road maintenance costs will be as hybrid vehicles age. Eventually, the hybrid's onboard batteries will lose their ability to hold a charge (just like any other battery) and will require replacement. The automakers claim that in 5-8 years (when large numbers of hybrids will begin needing new batteries) economies of scale will lower costs that today would be in the $800 and up range to half or less that. But no one really knows for sure -- and won't until we get there.

It's entirely possible that hybrid owners (or those who buy second-hand hybrids in four or five years) will face repair/maintenance costs comparable to the cost of a new transmission or other major work.

The best thing about diesels -- right now -- is the technology is already proven and known to be immensely rugged and reliable. In addition to excellent fuel efficiency (and high torque output) a diesel engine can be expected to run without major work for literally hundreds of thousands of miles -- well beyond the natural life of a gasoline engine or a hybrid gas-electric powertrain. And today's direct injection/turbo-diesels are quiet and powerful, too -- offering acceleration capability as good as or even better than equivalent gasoline burning engines. For example, the Mercedes E320 CDI can reach 60 mph in under 7 seconds.

The worst thing about diesels is their limited availability -- at least when it comes to passenger cars. Only Volkswagen (Passat, Jetta and New Beetle TDI) and Mercedes-Benz (E320 CDI) even offer passenger cars with diesel engines as of the 2005 model year. While these are all excellent cars -- and run the gamut from relatively inexpensive "fun" cars like the New Beetle TDI to the luxury of the E320 CDI -- you may simply want something other than a VW or Mercedes. And if you do, you don't have anywhere else to shop.

So how come there aren't more diesel-powered passenger vehicles?

The answer is, there are -- only they're not available here. In Europe, roughly half the passenger cars on the road are diesels -- which stand to reason in an area where a gallon of gas can cost as much as $4 (or even more). But the reason we don't get these cars here is because U.S. diesel fuel has a relatively high-sulfur content, which makes it harder for the automobile manufacturers to comply with current EPA emissions control requirements for passenger vehicles (trucks fall under a different, less strict standard). We're supposed to get low sulfur content "clean diesel" by 2007 or 2008 -- after which we can also expect to see more diesel-powered passenger cars on American roads.

But in the meanwhile, it's VW, Benz -- or the bus.

The final diesel downside is the sometimes limited availability of service stations that sell diesel fuel. Depending on where you live -- or where your travels take you -- you may find yourself running perilously close to an empty tank with no refueling facilities in sight. Unlike gas stations -- which always sell gas -- the next turn off up the road may have nothing for you other than meat snacks and a pay phone to call for help. It's not a major threat -- because diesels have huge ranges with a full tank, so you've got plenty of time to find a place that does sell the fuel you need. But it does require the diesel driver to give more thought to pit stops than the owner of a gas-burning (or hybrid) vehicle.

The good news is that within five years, at the latest, we'll have sorted most of these problems out -- for both diesels and hybrids. There will be many more diesels passenger cars available -- and as a result, the marketplace will seek to accommodate diesel owners by making diesel fuel readily available beyond just truck routes. At the same time, the up-front cost of hybrid vehicles should drop to a point where they are no more expensive (or hardly more expensive) than equivalent gasoline-burning vehicles -- so the fuel savings will be all gravy. And we'll know for sure what the down-the-road maintenance/upkeep issues will be, too -- including the replacement cost of those currently expensive battery packs.

In the meanwhile, the current crop of diesel and hybrid vehicles still offer buyers a way to get into a high-mileage vehicle that's not also a bottom-feeder economy car that's as cramped as a moped -- and about as much fun to drive, too.

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