Gas or Diesel?

The Diesel Rabbit got over 50 mpg - back in 1980.   Today, a few cars are offering diesel options.   Is the extra cost of a diesel engine worth the hassle?  Probably not.

When I lived in Virginia, a nice young couple moved in next door.  They hailed from Central New York, and his first remark to me was, "Wow!  It must be nice to live in a place where you can legally buy a Volkswagen Jetta Diesel!"

At the time, California and New York had instituted new emissions standards for diesel engines, and Volkswagen, at the time, could not comply with those new requirements.  So, for a few years, they were not available in those markets.

But it struck me as odd that he felt that a diesel car was like contraband, a coveted thing he could not have.  I wonder if he started smuggling them back to New York.

Diesel engines, by their nature, tend to be more efficient than spark-ignition (gasoline) engines.  And back in the 1980's, when we went through our last Diesel craze, many people bought them, not only for their high mileage, but because Diesel fuel was cheaper than gas.  And since they would burn home heating oil, you could put that in the car and pay even less than pump prices (although it was illegal).

Since then, new low-sulfur requirements for diesel fuels have drive up the cost considerably, to the point where diesel sells at a far higher premium than gas.   And in the interim, advances in engine technology have pushed gas mileage of spark-ignition cars into diesel ranges.  In fact, the highest mileage cars in America are now gasoline-engine hybrids.   Diesels are pretty far down the pack, most getting in the high 30's, while Hybrids zoom by in the 40's.   Many diesel cars are not getting significantly better mileage than their non-hybrid counterparts.

So, does buying a diesel car past the cost/benefit test?   It all depends on a number of factors - how much you drive, what kind of car you drive, what needs you have, and the relative cost of fuels.

And this debate rages on in the motorhome crowd, among boaters, and the like.   Sometimes diesels make sense all the time, sometimes they make sense some of  the time,  sometimes they make no sense at all.

The touted advantages of diesels are:

1.  Better fuel economy, as the engine is inherently more efficient.

2.  Better durability, as the engine is less complex and more robust.

3. More power, or more specifically, more torque, than a comparable gas engine.

The admitted disadvantages of diesels are:

1. Noise:  Modern diesels are quieter, but the caveat is "not as noisy as it used to be".  Still noisy.

2.  Smell:  A new diesel car is not the black smoky mess that you may remember from ages past.   But diesels tend to smoke more as they wear, over time, so don't be surprised if, down the road, you see that tell-tale black stain on your bumper, above the exhaust pipe.

3.  Fuel Cost: Today, diesel can be as much as a half-buck-a-gallon more than regular.  The increased cost of fuel negates any increased fuel mileage claims, unless you are getting at least 10% better mileage.

4.  Durability:  Modern lightweight automotive diesels are not the heavy monsters of yore.   And when they do break, getting them repaired can be difficult and expensive, as not many mechanics work on them.

5.  Fuel Availability:  There are more stations today that have diesel fuel, and there are always truck stops, of course.   But in many small towns, the only pump might have regular, and no diesel.   This is less of an issue today, and in places like Canada, not an issue at all.

6. Extra Cost:  Diesel Engines are usually an expensive option for most vehicles.  Recovering this cost can be difficult, if not impossible, unless you drive a lot.   Like a hybrid, the cost recovery in fuel savings may take years.

7. Winter Starting:  Diesel fuel has to be diluted with kerosene in the winter, or it turns to Jello and the car won't start - at all.   Modern Diesels are easier to start in the winter, but are still not immune to the laws of physics.   If your fuel was not "winterized" you may end up stuck.

So how do these issues stack up?  It depends on the vehicle.  Today, most heavy duty over-the-road trucks run on diesel fuel.  Well, just about all of them.   A few medium-duty trucks try to make due with a big-block Ford or Chevy engine, but even that market has largely gone diesel.   The high mileage driven by these vehicles pays back the extra cost, through fuel economy.   And the legendary durability of diesels pays back here as well.

For larger boats, diesels predominate as well.   In addition to safety issues (less chance of explosion) diesels are better suited for marine environments, and their high torque at low rpms are better suited for propellers than gas engines are.  Diesel engines are capable of putting out more horsepower as well, so if you need a big engine for a big boat, its going to be diesel.

For motorhomes, it is a mixed bag.  For an inexpensive Class-A motorhome, driven maybe 3,000 to 10,000 miles a year or so, a diesel engine is not going to pay back its extra cost over the life of the coach.  Such coaches go to the graveyard, often with less than 100,000 miles on them.  The longevity of a diesel is rarely put to the test.   And since these types of vehicles sit for long periods of time, they can be problematic, as diesel fuel does weird things when it sits (algae will actually grow in diesel fuel, I kid you not).

But what about passenger cars?  Back in the 1980's, going diesel was about the only way to get better fuel economy.  So VW, Chevy, Mercedes, BMW - just about everyone - offered a diesel car, if nothing else but to meet corporate fuel economy standards.  And diesel pickups started appearing in the lineups as well.

Pickups bear special mention, as many folks (men) believe you need a diesel for the power to pull a load.  And if you are hauling a 10,000 lb. travel trailer down the road, this is likely true - although you might want to ask yourself why you are doing that.   A friend had a trailer in this range and pulled it with both a diesel Chevy and a gas-engine one (the huge monster 8100 Vortec) and reported that the power was not an issue, but the 6 mpg while towing with the gas model, was.

(And let's face it - a lot of diesel pickups are sold to men who tow nothing whatsoever, but have, well, a need to compensate and play pretend trucker.  Just admit it and get over it.)


Compounding this is that pickup truck engines are not as durable as over-the-road truck engines.  Only the Dodge Cummins is really a "truck engine" (albeit a medium-duty one) and even it has been noted to have some maintenance issues. 

With cars, this problem is more acute.   It is not that car diesels are unreliable, only that gasoline engines are far more reliable these days.   Back in the day, you could say, "My diesel will go 300,000 miles between teardowns!" and that was impressive.   Today, gasoline engine cars are going this far - although not regularly.   And the reality of a diesel engine car is that after about 150,000 miles, it may start to smoke and need some valve adjustments and perhaps new injectors.  They are not maintenance-free by a long shot.  And if neglected, well, a diesel can bite you on the butt.  Water in the injection system can cavitate pumps and wear injectors.  And those fuel filters need to be changed often.  Oil changes are more expensive - and often more frequent, due to the high compression and high sump capacity.

So, does it pay back?  Well, let's look at my neighbor's Jetta, as that car can be bought in Diesel and non-diesel forms today.   The base Jetta TDI for 2012 can be had for a sticker price of $22,775 and is rated for 30 mph city and 42 mpg highway.  That's very good mileage, but not as good as a (more expensive) Prius.


The 2012 Volkswagen Jetta stickers for a much more modest $15,515 and gets 24/34 gas mileage.  By the way, I am not recommending either car, as they have been panned this year for having horribly cheap interiors, and a crappy twist-beam rear suspension.   But at 15 grand, they are cheap, no?  Sometimes price is king.

But getting back to our analysis, let's assume Gas is about $3.85 a gallon and Diesel is $4.15, which are today's prices in Brunswick Georgia.  Diesel and Gas seem to always have this 10% delta in prices, no matter how high or low they go.  If we drive both cars 15,000 miles a year (the national average), for 10 years, what is the overall cost?  Let's average the city and highway mileage together, giving the diesel an average of 36 mpg and the gas engine car an average of 29 mpg.

Every year, the gas engine car has burned 512 gallons of fuel for a cost of $1991.37

Every year, the diesel engine car has burned 416 gallons for a cost of $1729.16 or a savings of $262.20 per year.  While the savings in fuel are great, the delta in fuel cost negates about half of it.

Given the $7260 cost delta between the two cars, at this rate, it would take 27 years and 405,000 miles to start to see a payback by going diesel.  That is just a non-starter, as very few VWs will see that kind of mileage before they are wrecked or junked.

But what about maintenance?  Well, the base 4-banger in the VW is a pretty indestructible engine.  And gas engines no longer need "tuneups", as spark plugs can last as long as 100,000 miles.  And car diesels are not like their trucker counterparts, and are more prone to failure, and today far more complex than in days gone by.   So I am not sure you are going to get back this seven thousand dollar delta in repair costs, over time.

And likely, you will not keep the car that long, anyway, if you are a typical American.

Ironically, the VW Golf, the smaller hatchback to the Jetta, actually costs more than the Jetta, and gets worse gas mileage, in gas form because of their reliance on a harsh and crappy 5-cylinder engine.  Go figure.

The conclusion I reach, at least with regard to the Jetta, is that unless the dealer will discount the diesel model severely, you are just paying extra for not a lot.

The interesting thing, is of course, that in the race for hyper-mileage, many car makers seem to be drifting away from hybrids and diesels.   When a "base" model car can break 30 mpg without too much fanfare or hoopla, as the base Jetta does, what is the need to spend thousands of dollars per car on esoteric and expensive technology?

And from the consumer point of view, good gas mileage is a good thing - but hyper-mileage is not really a huge savings over "decent" mileage.   The problem with miles per gallon is that it is a fraction, and we all know from that girl in the third row who snapped her bubble-gum in class, fractions are hard.

Many economists point out that if we look at "Gallons per hundred miles" instead of miles-per-gallon, we might see the numbers in a new light.  43 mpg sounds great, but it is 2.32 gallons per hundred miles.  The lower mileage "base" Jetta gets 2.94 gallons per hundred miles, on the highway.   Viewed in that context, you can see that the difference ain't all that great.  And as I noted before, going from a standard car that gets about 30 mpg to a hyper-miler than gets 40 mpg ain't gonna save you much.

So, sadly, I have to reach the conclusion, yet again, that going to extremes to save on gas, while it might save on gas, won't save you much money.  And I say sadly, as I am a technology buff and think things like diesel engines, hybrid drivetrains, and electric cars are "cool" and interesting.

But alas, from a checkbook point of view, they don't really make much sense.