A while back I ran the numbers comparing my BMW 120d to a similarly specced 120i. If I remember right it will take about 50K miles for the costs to even out.
Again, also add to that the time you save by not having to fill up as often. Hybrid and EV owners can count that too, of course.
Why would you need to fuel up every 2-1/2 to 3 hours? That is only 200 or so miles. Even in the petrol cars I have owned, that is only half a tank, and only a 3rd of a tank for my diesel.
And I do take suitable driving breaks, but I don’t want to spend them on a forecourt filling up.
I said “a” break, not every break. I drive a lot of cross-country trips for work and vacations. I stop every 3 hours for a break to get the blood flowing even if my wife isn’t with me:D Heck, at work I get up once an hour just to relax the eyes and move some muscles (now a desk jockey instead of my preferred bullet juggling).
I was an early diesel adopter, 1984 Camry 1.8TD. Got great mileage, 45+, but I still filled up every couple of breaks. Combination of a small tank and not so many auto sized diesel nozzles back in the 80s.
A while back, I read that Peugeot-Citroen was designing diesel-electric hybrid cars-they claim amazing mileages (up to 80 MPG). This wold seem to be a much better design than a battery electric. Of course, this firm doesn’t sell in the USA-how are these cars/ (Clairobscure-merci?)
I don’t think anyone has released one yet, but lots of companies are working on them. If diesels are more expensive, and hybrids are more expensive, then it stands to reason that a diesel hybrid would be much more expensive. That’s why you haven’t seen them yet. In order to recoup the cost, either gas has to be really expensive, or you have to keep the car a long time.
It’s not $0.07/mile, it’s $0.07/25 miles.
Saves you $280 over 100K miles. Which does pay for itself, but is also pretty minor in the lifetime of a car.
How much is the price difference between the models?
Is there any different costs to maintaining the vehicles?
How much better does the tdi keep up its resale value?
True calculation of payback period requires knowing those things.
Oops, good catch. Like I mentioned, though, that’s mostly because the price of gas has plunged in the last few months and the price of diesel hasn’t quite as much. I’d expect “normal” prices would make the diesel look a little better.
A couple thoughts:
Diesel prices vary wildly where I live (Los Angeles), anywhere from LESS than regular to as much as a dollar more per gallon. No idea why this is and the prices seem to swing wildly even at the same station. Luckily the nearest one to us generally has cheaper diesel, as my wife won’t bother comparison shopping. But obviously this impacts the price comparison. For us it still makes sense–my wife’s old Caddy got half the MPG and took premium gas.
Peugeot and Audi now dominate the Le Mans circuit, to the point where they have had to create a separate category for diesels so the gas engines can win SOMETHING. I don’t know what the technology is, but I’m wondering if this will trickle into consumer diesel engines.
The price difference variation is interesting. I’ll look for other stations anfpd see their prices. My local Chevron stn has:
$3.63/g for 87
$3.73/g for 89
$3.83/g for 91 octane
$4.15/g diesel, so, $0.52/g more than regular
I’m curious about the time savings so will do the math. I keep my cars a long time and will figure on a 200K car lifetime.
*Gas: 200K mi @ 300mi per tankful = 667 fillups. @ 5mins/fillup = 55hrs (rounded)
Diesel: 200K mi @ 600mi per tankful = 333 fillups. 27hrs
Time savings = 28hrs.*
Wonder what I’ll do with that extra day I’ll save over the course of about 12 years of ownership. 
Assuming I buy that diesel Grand Cherokee, that is.
It already is, VAG (Audi, VW, Skoda) plus BMW and Mercedes already have a vast range of diesel engines that run (to USA eyes at least) at astonishing MPG figures and very high performance.
I just drove from UK to Austria and back in a 1.6 litre diesel engine car, fully loaded with ski gear and a family of four and returned 58 mpg for the full journey. That included booming along autobahn’s with the mental merc brigade and it kept up perfectly. Up and down mountains etc. Merging into the autobahns was never a problem as it has plenty of grunt. The technology is really rather mature now.
Not a definitive test but just a reflection on the “real-world” experience.
I found the numbers that I ran last year in this thread.
BMW 120d SE Coupe
2.0 litre turbo-diesel
173 bhp
53 mpg
£24795
Diesel price £1.42/litre
BMW 120i SE Coupe
2.0 litre petrol
168 bhp
43 mpg
£23965
Petrol price £1.35/litre
I only do about 12,000 miles/year but even then it would only take a little over 3 years to recoup the difference in starting price.
Peugeot has dropped out of sports car racing, they weren’t at Le Mans in 2012.
Why would diesels be more environmentally unfriendly?
Some other decent number crunching in that older thread, if I do say so myself.
Also from that thread I had posted a link which summarizedthis US National Research Council Analysis. That link is to the chapter on advanced compression ignition diesel technoogies (CI) and details their fuel consumption (FC) savings analysis, GHG analysis, and costs analysis.
Pertinent to the op is the chart on this page and following which details where the cost differential between spark ignition ICE (SI) and CI diesel technology comes from. This is for mid-size sedans:
It looks prettier in the link, but the total cost differential they believe should be $2393 with $688 of that being the emissions control technology alone but the rest various other more expensive systems, like a high pressure pump and so on. That analysis assumed high volume production.
They believe there is a potential for 33% overall fuel consumption (FC) reduction with advanced CI diesel technology (that’s in gallons/100miles). That’s a lot of savings for a bigger vehicle (like a Jeep Grand Cherokee) travelling many miles.
One additional issue is that American refineries are optimized to produce gasoline, not diesel. That raises the issue that the current greater drop in gasoline prices relative to diesel may not be so transient to the degree that it reflects more domestic oil production and regional refinery availability.
Crunch for the Jeep Grand Cherokee … according to this article
So diesel 4.17 g/100 miles and gasoline 5.26 g/100 miles. 100K means 4.17K g of diesel and 5.26Kg gasoline. Use the 2012 average prices and that means $19,031 on gas or $20,872 in diesel fuel - so a bit under $1100 savings in that 100K of driving and $2200 for that 200K you plan on. Huh. Not as big as I thought it would be. (Note fuel savings only, not factoring in retained resale value or differences in maintenance costs if any. Or the value of fewer gas stops or of decreased CO2 emissions.)
Not really. Last time I looked, diesel was costing about $0.50 more a gallon than regular gas.
The reason diesels have dominated the Le Mans circuit is because the rules have heavily favored them over gasoline engine. As an example, for the last couple of years turbo-charged diesels have been allowed 3.7 liters of displacement, while naturally aspirated gasoline engines have been limited to 3.4 liters, and turbo-charged gasoline engines 2.0 liters.
Reasons diesels cost more:
As has been mentioned, Diesel engines have to be stronger. You can’t use cast cranks or connecting rods, they have to be forged. Probably can’t use aluminum for much other than pistons, and those probably need steel caps. (this is changing, and some newer diesels have Al parts, even heads) Diesel exhaust valves need to be expensive, hard to machine alloy to stand up to the high oxygen levels in Diesel exhaust. Spark engines burn the exhaust valves if run over-lean…Diesels always run extremly lean.
Diesels don’t work so hot at high RPM, so you need extra displacement or expensive turbocharging to make enough power.
All this makes the engine weigh more, which will require upgraded suspension and possibly even larger brakes to stop the higher weight.
Injection system: Electronically controlled, hydraulic powered Injectors for modern diesels will cost around $150-200/cylinder. They also probably need a high-voltage driver/control system, which needs a bunch of sensors. Even old mechanical injected diesels needed precision injector pumps which run many hundreds of dollars. Spark ignition system is very cheap by comparison.
Vacuum pump. Most spark ignition cars have a number of systems that are powered by manifold vacuum: Power brakes, HVAC shutters, etc. Diesels don’t have manifold vacuum so you need a pump, and since it usually runs the power brakes it needs to be well made and reliable. In some cases the power brakes on a Diesel will be hydraulic boosted instead of vacuum, but this more expensive, and requires more engineering than just slapping a vacuum pump on.
Diesel exhaust still has LOTS of oxygen, which tends to corrode any steel in the exhaust system, so many diesels have expensive stainless steel exhaust systems.
Diesels need special heating systems for cold weather starting, and are very hard to crank due to high compression. So you need expensive geared starter motors, Thick copper wires to connect them to what are often dual batteries, and a bigger alternator to keep them charged.
A number of other options may come bundled with the diesel engine option:
Most diesels come stock with an AC powered engine heater, which is usually an extra cost option on a spark engine.
Diesels warm up slowly, so heated seats and windshield may be bundled with the diesel. Again, these usually cost extra with the spark engine.
In a pickup or SUV, people who want the Diesel often want it for towing trailers, so a trailering package and/or heavy duty suspension may be bundled with the diesel, along with premium tires or stronger forged alloy wheels.