Diesel fuel economy is a lie . . .

[QC]

. . . thought that might wake you up . . . Note I said fuel economy not efficiency . . . I have been noticing something over the last year that is very interesting to me. The percentage difference between Gasoline and Diesel continues to grow as well as the actual cost difference per gallon (percentage difference and cost difference do not always go hand in hand). Take a look at this graph I put together:

I got the data here, and it is consistent with pricing I have seen in CA and TX. The blue line is the percentage difference between the two fuels, and the yellow line is the cost difference.

Soooooooooo, if a diesel is generally considered to be around 20 - 40% more efficient, but the cost of the fuel is 45% higher, and the initial cost of the engine is more, thennnnnnnn . . . I think you can make a legitimate case that the owning and operating costs of a diesel are currently more than an Otto cycle engine using gasoline . . . I don't think that has ever occurred in the 30+ years that I have been in the engine business.

Yes, I know, blasphemy . . . Comments?

 

[Bob_VT]

Re: Diesel fuel economy is a lie . . .

Kind of explains my complaint about home heating oil prices not following the gas prices......

 

[JB]

Re: Diesel fuel economy is a lie . . .

Proof that statistics can be quoted to "prove" anything you seek to prove.

You have used only data for less than 2 months, when the price of gasoline fell precipitously and the price of Diesel fuel fell at a slower rate.

"Trends" quoted for a period of rapid transition are statistically useless, QC.

The last time that comparison was even vaguely stable was 2000-2005. Without looking, I think the "trends" were opposite of your conclusions.

 

[QC]

Re: Diesel fuel economy is a lie . . .

Thanks JB I said "currently", and I understand trends. I stand by my assertion. Today, diesel engines are more expensive to operate . . . I have shown a year actually. And the "trend" has been consistent for that long. I still maintain it is interesting, and I am not "seeking to prove" anything .

I'll repeat what I said . . . in the 30 years that I have been specifically involved in diesel cycle engines, their owning and operating costs, their potential use in different applications and using different fuels, this has NEVER been the case. Thanks for your support . . .

 

[angus63]

Re: Diesel fuel economy is a lie . . .

This comparison is for fuels, not for engines. Fuel is not the sole operation variable. If you add factors to the matrix like torque/horsepower per gallon,maintainance,durability, low volatility,adverse environment, etc... I think the scale tips the other way. I found the chart/data pretty interesting. Thanks

 

[QC]

Re: Diesel fuel economy is a lie . . .

I agree to a point Angus. There is also the energy per gallon discussion, and this gets very squishy when you add all of the variables. Buuuuut, Otto cycle engines are closer to diesel efficiency at high load factors, sooooooo, if you were comparing two 10 kW gensets in a boat, one diesel, one gasoline, that were both operating at 10 kW load, then theoretically the diesel "economy" would be significantly worse (not efficiency). At idle the diesel is waaaaaaaaay more efficient, so it might swing the other way. But, again, today, the cost is 45% more for diesel . . . That's a pretty big number to overcome.

Let me recite the I love diesel prayer so that I will be safe from further attacks:

Oh, Rudy, who art though in Heaven
Forgive me my sins
But give a nod to ole Otto for me
For today he has popped us all in the chins

Or something like that . . . :redface:

 

[SuperNova]

Re: Diesel fuel economy is a lie . . .

I agree that you would have to look at the costs over the lifetime of the engine to make a reasonable comparison. How much is the second and third gas engine that you have to buy to match the life expectancy of the one diesel engine going to effect your cost analysis? Of course, diesel oil changes are usually more expensive....on the other hand you don't have to buy spark plugs or pcv valves for the diesel.....hmmmm...course, if you get an injector failure or a high-pressure pump failure on the diesel........lol.

I agree with you QC, though, and I believe the fallacy of diesel economy was primarily propagated on the public in the 70's and 80's with the diesel VW Rabbits and such.

 

[QC]

Re: Diesel fuel economy is a lie . . .

Yeah, and you also have to evaluate the benefit of having the extra cash in hand from the lower purchase price of the gasoline engine . . . Net Present Value (NPV) calc . . .

 

[ebry710]

Re: Diesel fuel economy is a lie . . .

When we use to commercially consider diesel verses gasoline it was to justify the cost difference between the two technologies. Diesel obviously the more expensive unit.

You bought a gasoline engine if:
1) Short load distance
2) Inexperienced, multiple drivers
3) Frequent stops
4) Frequent trading in vehicle
5) Low service cost

You bought a diesel engine if:
1) Long trips
2) Heavy loads
3) Vehicles housing diesel usually have upgraded power trains, brakes etc
4) Experience single driver
5) Freeway driving where the number of gears and split rear-end keeps RPM to idea (better gas mileage or power)
6) Keep the vehicle for over 200,000 miles
7) Prepare for expensive service cost

I have always bought gasoline engines just because:
1) I am a short haul guy and constantly turn my engine off and on
2) I hate expensive service costs
3) I rarely tow loads exceeding 10,000#
4) And a properly equip truck with a 5.4 L gasoline engine, a matching 5 speed transmission, 4+ rear end and a programmable smart chip gets smart close to 19 mpg. I can't make up for the cost of a diesel engine.

 

[QC]

Re: Diesel fuel economy is a lie . . .

This is a guy who does his homework and doesn't simply follow sheep . . . ^^^^

Back to the diesel prayer:

I LOVE DIESEL ENGINES
But I love women too and sometimes both are wrong

 

[angus63]

Re: Diesel fuel economy is a lie . . .

This is a guy who does his homework and doesn't simply follow sheep . . . ^^^^

Back to the diesel prayer:

I LOVE DIESEL ENGINES
But I love women too and sometimes both are wrong

Today I moved an old Cleveland (GM) WWII 2 stroke from an attack sub across 150ft of laboratory. That heavy #$%^&* wronged my back.

PS You'll live longer if you repeat after me: Women are never wrong, Women are never wrong.......

 

[angus63]

Re: Diesel fuel economy is a lie . . .

I agree to a point Angus. There is also the energy per gallon discussion, and this gets very squishy when you add all of the variables. Buuuuut, Otto cycle engines are closer to diesel efficiency at high load factors, sooooooo, if you were comparing two 10 kW gensets in a boat, one diesel, one gasoline, that were both operating at 10 kW load, then theoretically the diesel "economy" would be significantly worse (not efficiency). At idle the diesel is waaaaaaaaay more efficient, so it might swing the other way. But, again, today, the cost is 45% more for diesel . . . That's a pretty big number to overcome.

Let me recite the I love diesel prayer so that I will be safe from further attacks:

Oh, Rudy, who art though in Heaven
Forgive me my sins
But give a nod to ole Otto for me
For today he has popped us all in the chins

Or something like that . . . :redface:

My diesel world has no wheels. I deal with electrical power generation and marine propulsion. In my world of continuous-duty, steady rpm, near-constant load, harsh environment, etc.... there really is no comparison. When it comes to diesels, your prayer is preaching to the choir!!

 

[JB]

Re: Diesel fuel economy is a lie . . .

For what it shows, QC, a snapshot of the last 2 months, your chart is correct. Historically, it is challengable.

I bought a new Mercedes 190Dc for $4200 in December of 1963. For the next 280,000 miles I got an average of 34.6mpg on fuel I never paid over $.22 for. I frequently paid less than $.10. It weighed 3200lb. No Otto cycle car of the time was in the same ballpark. 10-15mpg on gas that cost $.25 to .35 was typical. An exception could be made for cars that weighed under 2000lb, like the beetle, but they were trash long before 100,000miles.

Otto cycle car engines have gotten a lot more efficient recently, but only recently. The cars have gotten a lot heavier, so comparing a 4,000lb modern car with a computer controlled, turbocharged DFI gasoline engine to my 3200lb unsophisticated Diesel of 45 years ago requires math that I am not willing to do, and would probably be meaningless. Comparing them to a modern DFI turbodiesel car of 4,000lb probably makes more sense.

The problem there is that you can pick and choose models to produce whatever outcome you like. The 4,000lb Otto cycle cars vs. the 4,000lb Diesel cars.

In the case of the most advanced "Otto cycle" vehicles, computer controlled DFI, series dual turbos, that switch to Diesel cycle on demand but still burn gasoline, ethanol, propane, CNG or even hydrogen. MB calls them DiesOtto. I forgot what Ford calls theirs, but it is similar.

Now what? Are they Otto cycle or Diesel cycle? I say both. . .the best of both.

 

[angus63]

Re: Diesel fuel economy is a lie . . .

My olds vista cruiser used to convert on it's own for 5 minutes after I turned off the key and went in the house. I guess GM Rocket 350 cu in motors were ahead of their time!!

 

[chiefalen]

Re: Diesel fuel economy is a lie . . .

Diesel would be the way if we could grow and burn our own fuel, than it would cost you what? For seeds.

However diesel prices are high compared to gasoline and why i cant understand.

Gas is refined 2 or 3 steps further than gas.

Maybe someone can explain that one to me.

 

[QC]

Re: Diesel fuel economy is a lie . . .

a snapshot of the last 2 months, your chart is correct. Historically, it is challengable.

See, like usual, when we get down to the crux of the biscuit, we agree . . . My assertion was that today's diesel fuel pricing negates the associated engine's fuel effciency benefit, not necessarily even the last two months . . . Historically? Never before that I know of in the US.

 

[ebry710]

Re: Diesel fuel economy is a lie . . .

Diesel oil is a relatively pure cut of petroleum. Gasoline can be a pure petroleum cut or a cracking bi-product with a lot of additives.

Is diesel comparable to steak and gasoline in comparable to hamburger meat loaf.

 

[chiefalen]

Re: Diesel fuel economy is a lie . . .

It all comes back to the evil doers, the oil company's. Ha

But if you don't need gas don't buy it.

I wonder who said that ?

 

[wajajaja02]

Re: Diesel fuel economy is a lie . . .

gas 147 a gallon today, diesel 253. get 46 mile to the gallon in my tdi 2k vw bug. which had a 898 premium for the diesel option.
It has a hard time getting out of its own way, has gelled up multi times, even sitting next to the jd tractor with the same fuel that didint. and it needs a timeing belt every 80k miles, and now it has a glow plug sensor indicator alarm,intermittenly. its yellow and I call it LIPTON.
The engine might last for ever ,but the electrical harness will short out anyway, and the body will rust away around the engine that will fall out on the ground.

 

[DJ]

Re: Diesel fuel economy is a lie . . .

I tend to agree with QC. The major reason is that with further "emissionized" diesels, the efficiency suffers. When the efficiency suffers, so does the "economy" of said. As of today, we're talking about "on road" diesels. Off road is a bit of a different story but not for long. As California goes, so does the nation.

There are two ways to meet NOX emissions goals, with a diesel.

1. Exhaust Gas Recirculation (EGR).

2. Urea injection.

#1 effects efficiency by rerouting "spent" gasses into the combustion chamber.

#2 adds a layer of complexity/weight/expense.

As we approach 2012 (next EPA mandate level), the diesel argument is going to lose some ground. Note I say "some"-not ALL. Throw in fuel price uncertainty and-who knows?

Durability? As diesels get lighter/faster (RPM's) the durability question becomes just that, a question. Time will tell.

Many of my customers (fleet) are rethinking the whole diesel scenario for the following reasons.

1. Purchase price premium.

2. Fuel cost.

3. Application. If the unit runs a PTO or idles a lot, diesel starts to lose because of the Particulate Traps mandated for '08' and newer engines. The "trap" simply cannot regenerate at idle speeds. Not enough heat is built to accomplish the regen. goal. The same applies to most PTO applications. Not to mention, all regen. processes use additional fuel to accomplish the regen. process.

Diesel is not dead, by any stretch. Diesel engines can achieve goals that gas engines simply cannot, with any efficiency. For light automotive (class 1-5), it's getting fuzzy.

Let me add this. For ANYONE contemplating the purchase of an '08' or newer diesel. let me give some advice.

1. DON'T let it idle. Idling will KILL it. Particulate traps are a minimum of $1,800.00 and if you "plug it" you can't clean it.

2. Idling dilutes the engine oil becuase of the extra fuel injected during regeneration.

3. USE ONLY CJ-4 rated diesel engine oil. Any past rated oil will clog the trap. CJ-4 is backward compatible. I recommend it for any diesel, regardless of age. It's just cleaner.

2. Use an OEM fuel conditioner