A Tougher Case to Make. . .

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Is it still a good idea – from an economic point-of-view – to buy a diesel-powered car?

The answer’s no longer as clearcut as it used to be, when the answer was an unqualified yes. When diesel engines were simpler, cheaper to operate and more durable than gas engines.

When their mileage was much better – and diesel fuel much cheaper.

Diesel engines had fewer parts; they were (and still are) compression-ignition engines, so no spark plugs to wear out and and tune-ups  were a non-issue because there wasn’t really anything to tune. As long as the injector pump worked, the engine usually ran.

And it ran for a long time.

Hundreds of thousands of miles, usually without needing major work during that time. This longevity was a function of both simplicity (fewer parts, less to go wrong over time) and the necessarily stouter design of the diesel engine itself, which had to have a beefy (usually heavy cast iron) block and so on to handle the stresses of very high compression.

Diesel fuel cost less, too. Chiefly because it was a less-refined fuel. It cost less to make than gasoline. So it sold for less than gasoline.

And a diesel-powered vehicle used to use a lot less fuel vs. a gas-engined equivalent. Plus (and it was a big plus) you could use almost any type of diesel, including “homebrew” bio-diesel and even waste vegetable oil).

These factors quickly made up for the somewhat (but not hugely) higher up-front costs you paid to buy the diesel engine.

Today, the economics are much iffier.

First, the up-front cost are much higher. This is a function of the additional hardware – mostly emissions-related –  that modern diesels have to have in order to be legal to sell. Diesel-powered cars generally must have urea injection and particulate traps and these add a layer of maintenance and repair costs to diesel ownership, in addition to higher costs up front. If the car has urea injection, one must regularly refill the urea tank – a small but not irrelevant cost and additional hassle.

And modern, EPA fatwa-friendly diesel engines are more rather than less complicated. They are also more finicky about the fuel they’re fed, which (generally) must be low or “ultra low” sulfur diesel, which is more expensive because it now costs more to make it than gasoline. You generally can’t use inexpensive, home-brewed fuel, either. At least, not legally. And probably not without violating the terms and conditions of your warranty coverage.

The mileage isn’t fantastic, either.

Many new gas-powered small cars (and some mid-sized cars) are capable of almost 40 MPG on the highway; the handful of diesel-powered cars you can currently buy are capable of doing better, but not spectacularly.

Example: one of the few diesel-powered cars not fatwa’d off the market is the Chevy Cruz diesel, which could go 27 MPG in city driving and 46 MPG on the highway. This is very good. But a gas-engined Mazda6 sedan can go 25 MPG in city driving and 37 MPG on the highway – which is nearly as good. And the Mazda’s price – $21,495 – is much better than the price of the Chevy – $25,660 for the 2015 model (which is the last year this model was available; Chevy also had to pull it off the market because the ’15, while “clean” by any sane standard, isn’t “clean” enough for Uncle’s current not-sane standards).   

If you bought the Chevy over the Mazda, you’d have spent $4,020 to save 2 MPG on fuel in city driving and 9 MPG on the highway. Average it out, it’s about 7 MPG.

Call it ten.

It still doesn’t make much, if any, economic sense to buy the diesel.

It might, if the gas-engined Mazda’s lifespan was much lower – as used to be the case, gas engine vs. diesel engine. But it’s not the case today (and hasn’t been, for many years). It’s routine for gas-engined cars to run reliably for several hundred thousand miles – as opposed to maybe one hundred thousand miles, as was the case once upon a time.

A diesel engine may still out-last a gas engine, but after 20 years and 200,000 or so miles, who’s counting?

And modern diesel engines – more complex, not as maintenance-free – will probably not last as long as their forbears and will almost certainly cost more to keep going over time (see the part above about the urea injection systems and particulate traps).

Meanwhile, gasoline costs less than diesel – which further undermines the economic case for the diesel.    

Even the performance case is not what it once was.

Diesels used to have a huge advantage, torque-wise. They made a lot of it – and made it early, low down in the powerband. This gave the vehicle strong performance accelerating from a standstill and also in the mid-ranges; it wasn’t necessary to “floor it” to get a diesel-powered vehicle to move with authority.

But gas engines do that now, too.

In part, because – like diesels – they tend to be turbocharged. And these turbos are not the peaky (and laggy) turbos of the past. They are twin-scroll and multiple/staged turbos that build boost almost immediately, without lag – and very much like a turbo-diesel. Take a look at the specs of any of several currently available turbo-gas powered cars. They offer big torque (and peak torque) at barely-faster-than-idle RPM speed (in some cases, as low as 1,200 RPM but generally, most of them make their peak torque before 2,000 RPM… just like a turbo-diesel).

And they make horsepower, too.

Many diesels are deficient on that score; they pull hard initially – but generally haven’t got much on tap higher in the power band. They are down-low engines. But modern turbo-gas engines are good down-low and up high.

So, is there any good reason to consider buying a diesel engine?

If you need to pull/tow a heavy load then a diesel is still a good choice. This is why diesel engines are still readily available in pick-ups trucks, especially big ones. Which also have big diesels (such as the Cummins turbo-diesel V8 used in the new Nissan Titan XD) that make superhero torque.

If you like long legs. A diesel-powered Mercedes E-Class ($52,650) isn’t exactly economical, but it can take you almost 900 miles (886.2 to be precise) on a full tank, highway miles. This is a function of the diesel’s being in its element on the highway and also of the large (21.2 gallon) fuel tank the car has.

It’s worth noting that while diesels are almost unavailable in modestly priced cars (VW had to stop selling them, per Uncle’s fatwa – and Chevy had to temporarily/”voluntarily” pull the Cruz diesel until it can be made Uncle-compliant) you can still find diesels under the hoods of high-end (and high-priced) stuff.

Precisely because economic considerations are no longer the main consideration for considering a diesel engine.

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39 COMMENTS

  1. The only advantage today’s diesels seem to have is that they give luxury cars longer legs than they wouldn’t otherwise have. So diesels may be a way to make modern day luxury land yachts like 7-series Beemers and S-class Mercedes economically viable in terms of CAFE standards.

    That’s about it, because today’s diesels offer none of the purchase price, operating and maintenance cost, economy and reliability advantages that they used to.

  2. Eric, for me another reason to abandon diesels is the vast improvement in the behavior of gas engines. In the 1980s I vowed to never again own a vehicle powered by gasoline. The newspaper I worked at ran a weekly column by a mechanic. About 80 percent of the letters to him read, “Dear Dave, my 1984 [make, model] surges and stalls. I’ve had it back to the dealer 12 times. What could be wrong?” Meanwhile, as long as it had fuel and air, my little Jetta turbo would never miss a beat. Hey, who minds carrying a 100-foot extension cord to plug in the block heater, or spending a Saturday afternoon installing a fuel warmer? One must be reasonable! Nothing could outweigh my contempt for those sputtering, spark-ignited crapwagons.
    But now thanks to electronic controls, gas engines fire right up without touching the accelerator (it used to drive me crazy, btw, when people would pump the throttle in my car and rev it up when starting. Keep your foot off the damn accelerator, gas-burner moron!). I bought a cheap little Ford Focus in 2005, and it has always started and run flawlessly. In fact we now have three Foci. While they can’t touch the 60 mpg of the old Jetta, they are pretty efficient by today’s standards, and more importantly, they run just fine. Good little appliances.
    So, I still have my old Dodge/Cummins pickup, a new common-rail John Deere tractor, and a monster lawnmower with a liquid-cooled Kubota diesel, and I’ll never forget the sweet sound of the big Cats I drove all over the country. But thanks to the genius of engineers and the evil of government, I don’t foresee owning a diesel-powered car again. Who would have thought?

  3. All of which makes one wonder why, since the patents have long since expired, why none of the manufacturers have developed and adopted the (Nikola) Tesla turbine, which would run on anything combustible with very low emissions.

  4. You forgot to mention one advantage of the diesel. You can store diesel fuel at home for long periods of time and it does not go bad or deteriorate, you can’t do that with petrol it deteriorates quite quickly.

    • and if yu happen to still “heat” with fuel oil you can get the fuel truck to deliver bulk oil far cheaper than pump fuel…… long as the staters don’t catch you running non-taxed fuel. Its the “old stuff”, still has the normal amount of sulphur (which helps lubricate the injection system better than the low S fuel). That stuff can store for years and still be viable. Of course, that does not help when out on the road running interstate.

  5. Eric,

    new time reader. what do you think about picking up an older mercedes diesel sedan? not sure which years would be best. whats your thoughts? mpg is important, but simplicity is also. thanks

    • Hi Ralph,

      You are thinking right! The older Benzes (300D, etc.) are unkillable. Slow, but eternal. They never die. Decent mileage, too – but the real sweet spot is the longevity and low upkeep.

      I commend them to you!

      • and I heartily second that. I’ve owned, and mainteined for customers, a number of these That engine is fitted to four door sedans, wagons (HARD to find….) and two door couples. All are in the 123 body series. Comfortable cruise at 85, typical mileage high 20’s low 40’s at a more sedate 70 mph. The rest of the ar is built like the engines…. rugged, tough, works well, easy/cheap to repair. The 300 SD series, the 126 body cars, are more plush, tend to get a bit better fuel mileage, I’ve sometimes fitted a HUGE Racor fuel filter in the fuel system )between tank and lift pump) with the replaceable2 micron filter element, centrifugal water/particulate separator, and dumped waste/drain oil into the tank… a gallon for every fillup. No difference in engine performance, “free”fuel (the oil is now worth the going price of diesel fuel per gallon, rather than being sumped/recycled for someone else’s profit). And the oil is heavier, so burns with more energy per gallon. Filter the “big pieces” out before pouring into tank.
        I’ve found a couple of these with heavy oil smoke and oil consumption. A quick check can tell if its the turbo seals… they fit a high quality Garrett hairdryer. the bearing and seal kit can be had for under $200, takes four, five hours to tear down, clean, rebuild back to new condition. A reman unit runs about $1000 to $1200 in the carton, needs changed. If yuo can find one of these with a worn out turbo at a low price, those can be a bargain.

  6. What we have is a monster agency with no checks and no balances.
    That might be about to all change with the election or not. Still too early to tell whether or not the opposition will succeed in keeping Donald out of the White House. (If they do, I see a revolution in the works.)
    What kind of gas is coming out of the back end of one of these diesels and how does it actually effect the atmosphere? What I am seeing is a cold vortex right now with below zero temperatures over much of the USA. That vortex kind of blows away the idea of global warming or does it?
    Unlike Oxygen, CO2 conducts temperatures much better. Meaning at one point the entire planet might equalize out instead of drastic changes in temperature. So below zero temperatures and higher temperatures at the poles might become normal.
    What I am seeing is an EPA reluctant to tell the truth about anything.
    That is the appearance of things not necessarily all about the truth of things.
    Currently in small town, USA, I see 40,000 vehicles traveling one street alone each and every day.
    (We clocked it with a wire across the main roads.) And that was in the mid-80s.
    It isn’t what any one of those vehicles produces in the way of Carbon Monoxide and Carbon Dioxide. It is basically the compounding result of all those vehicles on the road.
    What we really need is competently designed engines with the current technology and engines designed to last a long time. The later is not going to happen as long as the current bunch of thieves design cars. They are designed to fail and probably within a short period of time after purchase(2 to 5 years) and that is the real reason diesels are on their way out the door. The messed up big time when these same people allowed lead to be taken out of gasoline. It made the cars last too long and that alone will bankrupt the big 3 in this country.
    It is all ready happening.
    What they have done is complicate engines so you need a master’s degree in engineering to keep them running vs. a backyard mechanic in years past. Even that has not stopped the American Public from redesigning a lot of cars underneath the backyard apple tree.
    Anything to keep the flow of sales going in automobiles.
    The technology currently available makes these manufacturers fairly close to dinosaurs. So how do they stay in business? One way is the EPA in their back pocket keeping current tech from making a difference in the design of an automobile.
    IF I were to design something better, they would take it off the market as soon as possible.
    For instance, design a propane diesel with a hybrid electric engine so that it automatically gets way over 150 miles per gallon of diesel fuel. Or redesign an engine to run on water. (Break the water apart and use the hydrogen and oxygen separately as a compound fuel. Use a catalyst to make it easy to break the water apart–just a suggestion)(You compound the water into something else, then break it apart easily) If you want to try it, find a really rusty nail. Throw it into a jar with a 1.5 volt battery wires and test tubes. It will literally double the oxygen coming off when you use the voltage to break down the water.
    I am no engineer. I am no mechanic. I am no scientist. Just an average person in the middle class. If I can see those possibilities, why cannot the genius level engineers see it also?
    One reason no diesel and no electric engine will become really common is simply it will destroy the gasoline engine industry both from the fuel and the car standpoint.

    • VW has such a car, the X1, being tested in china. A 27 hp diesel that charges batteries. The car gets between 150 to 300 mpg in real world driving. The green groups are behind the VW run down as an X1 on the roads would destroy the green agenda. Rothschild, who funds the green groups, doesn’t like this as it conflicts with his strategy to destroy the middle class.

      • 1982 V W Rabbit Diesel I bought a mint example of one of these for 3K(high but mint) a few years ago. The vehicle is a exercise in the “less is more” ethos. It get mid 40s to the gallon under all driving conditions. Driver visibility is the best of any car I have ever driven… which is important in avoiding accidents which you def want to do bc the thing weights about 1800#. My only complaint is that its noisy and vibrat-y. No electric anything. Nothing ever breaks on it!. I bought it for SHTF.

  7. I recently picked up an ’03 Jetta Wagon TDi with about 150k miles on it for $3200 off of ebay. Before the VW fiasco a Jetta Wagon TDi could get nearly $10k. Bunch of little crap busted due to neglect and the intercooler crapped out due to EGR clogging, but parts are cheap – I picked up new made in Taiwan wheel liners for $10 and a new intercooler can be had for $70. Easy to work on, too. And since it’s a cheap used car, the cosmetics don’t bother me.

    So pick up these cheap diesels while you can. I’m guessing there’s another round of “Cash for Clunkers” coming up, maybe this time targeting all those “dirty” diesels.

  8. So if a fella (or gal) were looking for a good used diesel vehicle for a daily driver (some highway, mostly city), what might be some good options? Pick ’em Up truck, sedan, doesn’t matter.

    • Hi Larry,

      For a car/daily driver, I’d look for any TDI VW made prior to 2015; i.e., those without urea injection. They are outstanding vehicles that typically deliver better-than-advertised mileage. For a truck, I’d go with any model built prior to the elimination of mechanical injector pumps.

      • except that the earlier pickup diesels with mechanical injection don’t get very good mileage… most are in the low teens empty, a bit less working. they do run forever, but nowhere near the power. the best, in my vies are the 7.3 Powerstrokes.. electronic fuel injection, 17-18 fast freeway cruise with the low geared rear end, about 1.5 more with the taller one. BUT.. put a load behind that and the mileage doesn’t fall much like it does with a gasser. I’ve towed a 24 fot long cargo trailer ,9/6 hjihg, 8/6 wide, putting 14K on the four tyres and 2500 on the ball, freeway speed and gotten 14 mpg. that’s better than the same van with the small gas V8 can get empty….. load that thing down and you are in the mid to high single digits. AND I’ve now got 330K on mine, except for a brearing/sea; kit tossed into the turbo nothing done. It still does not use any engine oil betwen changes, and I’ve extended the change interval to more than double. Inside of the engine still looks like new.

  9. 2001 7.3L Power Stroke Diesel, crew cab, full size bed – 185000 miles. Have had to fix some minor things, but, so far, nothing major. And actually, compared to other PU’s with even mid-sized gas engines, it gets better fuel mileage with a much larger load capacity. Plus, in a pinch, I have many more options other than ultra low sulfur fuel. Like the gentleman above with the ’92 Dodge, I’ve had phone calls from dealers asking if I wanted to sell it. No way!

  10. Welp,

    I’ve got one of those “bad” diesels from VX. I get 40+ MPG in mixed driving. My previous car required premium gas, so the diesel fill up is cheaper, generally, than a fill up of premium gas in my old car, and I’m getting 40% more mileage or more. Generally, I’ve experienced lower service costs for the diesel as well, so I’m leaning towards “me like”. I’ve got a 2012 so I assume that has all the diesel emissions on it (I’ve got the urea tank).

    Would I get another one? For all the reasons listed above, yes. “No” for it being a sedan and a automatic, and it’s not that “sporty” in looks or behavior. However, it is a stealth car. Cops don’t tend to notice a bland sedan that isn’t flashy…..

  11. I live out in the country and my only vehicle is a ’92 Cummins diesel Dodge truck with only 160K on it. I can’t tell you how many times I get an offer to buy it. I would never part with it.

    • Hi Karin,

      I’ll bet! Your Dodge hasn’t got all the latest (expensive, efficiency reducing) EPA-mandated “emissions” equipment. I’d like to have one like that, too!

      • The thing is I am not against protecting our plant and the air we breathe but I think each individual human should bear that responsibility. I know my truck probably pollutes more than a brand new piece of junk but I only go out to town which is a long drive about once every other week. Part of that is to preserve the truck but it is the least I can do to keep the air in this beautiful part of the country clean. Then I can burn more wood in my fireplace 😉

        • one “envrionmental load” few of the greenies ever mention (none I’ve ever heard so far) is that of repair/maintainance/replacement as the vehicle wears out and needs repaired. The older more traditioinal diesels that push the rig for half a million miles last twice as long as even the strongest of their gasoline burning counterparts. and often do more work for less fuel in the process. Soo maybe that VeeWee poops a tiny tad more of some nasty stuff (per EPA, what do THEY know anyway?) but uses far less total fuel/emissions per mile than the compliant ones…. and since it lasts twice as long the environmantal load of building a complete new car is saved. So, Karin, keep your old Dog running…. at 180K its still a youngun. Mayb e halfway there. By owning a vehilce that will run a LONG TIME you are reducing your “load” on the planet signficantly.

  12. I took a dislike to diesels when I was young and worked for a construction company. Part of my job was trying to get truck diesels started that sat in serious winter cold for weeks and months. When they did start, with copious amounts of ether, they rattled and snorted and stank everything up. Then GM came out with their converted-to-diesel gas engines which were junk.

    Times change. Diesels are more civilized now. But for light truck and passenger car applications they still don’t look enticing. The staff of the Under the Hood car fix-it radio show note that unless you put a pickup diesel to hard work fairly regularly, you’re just wasting money and, if I understand them, actually shortening the life of the diesel engine. There’s also the problem in our brutal winters of keeping diesel fuel from gelling.

    I asked my diesel mechanic brother once why diesels outlasted gassers. He thought it was because they were heavier built which makes sense, but the implication is that gas engines could be equally long-lived if they were just more sturdily built.

    • Hi Ross,

      My 50: Were it not for the evil one-two punch of government “safety” mandates – which have made all vehicles obscenely heavy – and emissions standards that have gone from reasonable to extremely not-reasonable – we’d have 100 MPG diesel-powered economy cars and 60 plus MPG diesel powered family cars.

      That’d be worth the extra outlay…

      • So true Eric, and the emissions controls are now causing problems in London and Paris that didn’t exist before. It can all be traced to these new “emissions free” motors being dictated by government and those useless prickly car companies run by accountants. The second worst scum after economists. And why NY and LA are not cleaner air wise. The chemistry of the newer motors is more deadly than the older motors, I can tell you that as a chemist.

    • The idea that a big diesel not working hard very often leads to early failure is nonsense. A diesel runs more efficiently at part load condition, and, assuming they reach normal operating temperture range during their duty cycle, willl still fun forever. Longer the more easily they are worked. My big 7.3 can really move out when I kick it, but mostly I drive it gently…. and at 330K it has needed nothing but a turbo rebuild and still does not use oil between changes… I NEVER add oil. At times I work it hard.. I’ve run quite a bit at GCW of 26K. It still don’t care.

  13. Once they lost the injector pump and went to all the electronic high-pressure injection, that was the end of diesels for me. Last diesel I had was a Ford 6.9. They’ve lost the very things which used to make them desirable, as your article states, Eric: Simplicity; durability; economy; reliability.

    If it’ll run without the battery/alternator hooked up, it’s a real diesel. These modern abominations are just engines which run on diesel duel- not real diesels!

    The average schmoe has not figured out that their is no economic benefit to these diesels. 17 year-old diesel pick-ups with 200K miles on them are selling for RIDICULOUS prices- often 2.5 times as much as the same truck with a gas engine. Even if the buyer got a 100K trouble-free miles out of old truck (not gonna happen!) it STILL wouldn’t be worth the premium, because he’ll never even come close to making up the price difference in fuel costs with that extra 4 or 5 MPG.

    • Yep, aside from the starter, the only electrical gizmo that my P-pump ’95 Dodge/Cummins needs to run is the fuel shutoff solenoid. And that’s the only part of the engine that has ever given me trouble.

      • My 93 Chevy Turbo Diesel only needed the lift pump to run. A friend’s 92 Ford Powerstroke was the easiest to start without a starter though. He worked it for months by only stopping at his house/barn on top of a steep hill. He’d get in, clutch it and when it got up some speed he let off in 3rd and away we’d go. All his fields were in valleys with steep pasture roads to them. He’d laugh and say “someday I’m going to replace that starter”. He had a Dodge he put new injectors in at 340,000($2400 jobber price + installation). He thought it was a good deal. I’d guess he was right since it still ran but not like it had and not good mileage till the new injectors.

      • Yeah, those Cummins fuel solenoids always quit eventually, and often not at a convenient moment. You can actually just take them out and the engine will start and run, but you have to kill it by stalling with the clutch – unless you have one with a manual shutoff (those were the best deals!).

        • My old Cummins NA 250 fitted to m Kenworth COnventional dumped the electric fuel shutoff solenoid on the road one time. I hitchhiked to the next town, found one ($50) hiked back, swapped it out, and made my day’s load anyway. A year later it died again….. but meanhwile I had figured out it had a manual bypass screw, which I then turned to the OPEN position. Engine had a conmpression release lever so I’d simply yank that monkey by its tail and the engine wouild rumble to a stop. Fuel valve was left in the OPEN position constantly. Ran it that way for a few more years, refusing to spend fifty bucks for another valve that woiud break again, stranding me. That part, and the bearings on the generator (yes, generator) are the only things up front I ever dealt with. Oh, a water pump… a reman cost me $45.

        • I’ve always assumed that the demise of the simple fuel shutoff knob was part of the dumbing down of the diesel: Had to make it act like it had spark plugs so the average government school graduate wouldn’t be complaining “Why won’t this thing stop?”
          Sort of like how they’ve dumbed down personal computers so users don’t have to understand what a file is or how folder structure works. In their effort to make computers so anybody can use them without learning anything new, they make things worse for those of us who long ago took a few minutes to understand a teensy bit about what makes them tick. I don’t know how many times I’ve tried to explain folder structure, comparing it to a file cabinet with folders containing papers (and sometimes other folders). Eyes glaze over and the original complaint is repeated: “I know I saved it; why is it gone?”
          I actually did make a manual shutoff for my ’95 Dodge when the solenoid became unreliable. It worked OK, but it made an constant rattling sound that I couldn’t figure out how to eliminate, so one day I stuck the old solenoid back on. It’s been working flawlessly now for 15 years.

  14. Modern turbo-diesels operate at far higher pressures than any gasoline engine, so they’re likely to be less reliable than even turbo’d gassers.

    I’d pass on any modern turbo-diesel in favor of a 300D, unless I was leasing (turning it back in before the warranty expires.)

  15. When I ordered my VW T6 California last year, I had a choice of Gasoline or Diesel. I chose Diesel because, dispite the consumption claims of the two options, Diesel is much more economical in real world driving. It also has a higher resale value.

    • Diesel also stores for 10 years to gasoline’s 6 months (untreated for both). And in a disaster, there will be long lines for gas, but few lining up at the diesel pump.

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