Am I analyzing this right? Diesel vs Petrol

midwest x6 · #1 02-26-2011, 07:36 PM

I know this has been discussed a lot, but does this seem clear that it was an economical plus to move from my tt v8 to Diesel?

1). Petrol Premium: $3.659/gal
2). Diesel: $3.899/gal
Difference = 7% premium for Diesel

3). TTV8 Mpg = 14 avg
4). Diesel Mpg = 21.8 avg
Difference = 56% better gas mileage for Diesel

What am I missing to draw an accurate conclusion?

Richard in NC · #2 02-26-2011, 08:19 PM

That shows the diesel will cost less to operate. To determine how much it saves, you have to add in miles per year and calculate actuals to get savings per year. To decide if its worth it, factor in the cost difference between models, and any costs/savings to trade and how long you are keeping the car.

JCL · #3 02-26-2011, 08:30 PM

Quote:

Originally Posted by midwest x6

What am I missing to draw an accurate conclusion?

1) 1st question is what will happen to fuel prices in the medium term. Assume your figures are right for now, but it is more likely that diesel will rise more quickly than gasoline, due to refinery capacity. That isn't for sure, but it is widely forecast. Suggest you don't worry about it for now, as nobody knows for sure.

2) 2nd question is whether those are actual mileage figures. If you owned both vehicles, and measured over full tanks as opposed to relying on the on board computer readout, then you likely have better data than having to rely on government fuel consumption figures.

3) 3rd question is whether that is summer or winter diesel. Winter diesel will usually produce lower mpg due to lower energy content than summer diesel.

4) Once all the above is qualified, then all you are missing is the formula. Fuel prices and mileage figures as you have shown them are hard to combine together, what you need to calculate is the $/mile. Using your figures, the diesel is costing $0.18 per mile, and the gasoline model is costing $0.26 per mile. Assume the same maintenance costs. Savings of $0.08 per mile equate to a 32% improvement, and will allow you to calculate a payback period (in miles) based on how much it cost you to move to the diesel, if anything. ie, for every $1000 of cost (purchase price, taxes, etc) you will have to drive just over 12,000 miles to break even. OTOH, if the diesel was cheaper, you are already ahead.

midwest x6 · #4 02-26-2011, 10:11 PM

Very helpful and intuitive too...

Thank you both!

Kloogy · #5 02-27-2011, 01:26 AM

How many people that buy these vehicles really care that much about fuel consumption ? I know I don't. If I did, I wouldn't be buying this type of vehicle.

deutsch100 · #6 02-27-2011, 11:42 AM

Quote:

Originally Posted by Kloogy

How many people that buy these vehicles really care that much about fuel consumption ? I know I don't. If I did, I wouldn't be buying this type of vehicle.

100% I bought the diesel for the amazing torque & I just love the sound of a diesel. When I traded my 2010 750 for the 2011 E70, I really loved the looks and technology of my 7, but it just made me feel SO old and stuffy driving it & it is so big (I am 36!).

The Eco Credit and Diesel tax credit for sure played a part in me choosing the 35d, but even without those benefits...I would have chosen the 35d over the 35i. I think the 35i is an awesome engine, but I prefer the 35d. If I would have not gotten the 35d, I would have for sure chosen the 50i.

To me, the better fuel mileage is just a side benefit, along with much lower AAA car insurance (about $800/year lower than the 2010 750). Now that diesel is more expensive than Premium fuel (damn middle east and their craziness!!

the fuel benefit is minimal, but I love me some diesel!! And look how clean the 35d tailpipes stay, opposed to the 35i and 50i

ard · #7 02-27-2011, 01:46 AM

^^ Pretty much agree.

I liked the diesel for it's superior performance.

JCL · #8 02-27-2011, 02:28 AM

Many purchasers of the diesel models were driven at least partly by the advertised improved fuel consumption over gasoline models. There are enough posts on here about the real world mileage of diesels to conclude that.

Opinion now. I think in many cases it is a feel-good thing, or part of a rationalization, rather than a calculated economic benefit, but a percentage of those purchasers (such as the OP) want to take it one step further and see if there is a financial benefit.

midwest x6 · #9 02-27-2011, 11:03 AM

Quote:

Originally Posted by JCL

Many purchasers of the diesel models were driven at least partly by the advertised improved fuel consumption over gasoline models. There are enough posts on here about the real world mileage of diesels to conclude that.

Opinion now. I think in many cases it is a feel-good thing, or part of a rationalization, rather than a calculated economic benefit, but a percentage of those purchasers (such as the OP) want to take it one step further and see if there is a financial benefit.

Hey -- Every time I spend over $60k for a vehicle I'm looking for rationalization too

ard · #10 02-27-2011, 12:52 PM

Interesting thread- I like seeing what motivates buying decisions around diesels... fascinating.

I was talking to a friend who said "I need a new car, has to be an SUV for the kids... not too big, we have a Tahoe for long road trips, and it has to be luxury- life is too short". So I said "Check out the BMW X5". Her reply "Oh, it needs three rows of seats, sometimes I need to cart around their friends". I replied "It has a third row option". "Oh, really?" "Yes, and you should check out the diesel- fantastic power, amazing mileage, really well behaved".

Her response? "Oh, I don't know...it's such a hassle finding fuel, and they are really noisy"

Facepalm.

So I need to steal the wifes X5 and take it to work one of these weeks for a test drive.

A