Pig Piss

[shatto]

Now that the government has forced y'all have to add pig piss to a separate tank to make your diesel engine run clean....
What sort of MPG do you get and how has it affected your overall operating costs?

[Lug_Nut]

Fortunately it is nearly odorless since it it synthetic, unlike the dinosaur piss that's passed off as gasoline and as petroleum diesel.
One drawback is that it requires higher temperatures to function than can be maintained in highly efficient models. As a result the Golf and Jetta common rail TDI don't have this urea additive, but the thirstier Passat common rail TDI does.

The urea tank, at least on the Passat, is sized such that its just under 5 gallon content is expected to last at least 10,000 miles, but could last as long as 50,000 miles. So figure something in between, 25K miles seems reasonable between re-fills.
The urea additive is available on the shelf at most of the chain auto parts stores around here, so it's no longer a dealer only item.
I just googled up some on-line sellers and got prices of $10 for 2 1/2 gallons, so $20 would fill the tank for 10K to 40K miles (YMMV). Each 100 miles would cost 5 cents in additive (at 10k rate), to 2 cents (at 40k rate)
Is it worth it?
The Golf and Jetta are EPA rated at 30/42/34 but don't use the urea injection.
The Passat is EPA rated at 31/43/37.
Fuel would have to be free to not amortize the additive cost

The 2012 Passat TDI, during my hour + test drive in one, returned an indicated 51.4 mpg on a loop in the Boston area. I drove my own '05 Passat TDI on that same loop, finishing within 2 minutes of the time, and obtained an indicated 36 mpg in mine, which is pretty close to my ownership average in the '05. I expect the '12 would average close to the 50 mark the way I'd drive.

[shatto]

Have you been using it long enough to know the maintenance aspects?

[Lug_Nut]

No, I am fortunate enough that my diesels are older models (1988, 2000, 2002, 2005) and are compatible with B100 biodiesel.
The newest diesels need all sort of added emissions controls to make the petroleum diesel exhaust meet the current unified emissions standards. The pity is that the controls and devices needed to make petroleum fuel emissions clean enough preclude bio-fuels over 5% from being used.
So without that level of emissions controls I can run a cleaner renewable fuel and have a lower emission exhaust than a more complex system to get fossil fuel emissions as low. No, I won't be getting a "clean diesel" any time soon as I believe they are mere 'greenwash'.
As far as maintenance aspects of the urea systems go: I do have a number of friends and acquaintances that have these systems. To paraphrase one: the maintenance is less than they use on their windshield washer fluid.

[trollbait]

As a result the Golf and Jetta common rail TDI don't have this urea additive, but the thirstier Passat common rail TDI does.

The urea (SCR) systems allow the vehicle to operate in the efficient, lean range diesels excel at. So the vehicles should have little to no hit to mpg. The others use an EGR system to control NOx, which tends to hurt their efficiency. It's how Honda also controlled emissions on the diesel Accord they had planned to bring over. It's EPA rating was lower than expected, and they cancelled it. At the time though, urea injection was still new, and people were resistant to it.

Now that the fluid readily and reasonably available, I think many potential customers see the advantage of the system. Last report was that the diesel Cruze would have a SCR system. Too bad it will be the 2.0L and not GM's smaller diesel.

The pity is that the controls and devices needed to make petroleum fuel emissions clean enough preclude bio-fuels over 5% from being used.

More precisely, the cost cutting way they are implemented limits the use of bio-fuels. The DPF needs to be sprayed with fuel for the regeneration cycle. Most manufacturers have chosen to inject the required fuel into the cylinder during the exhaust the stroke. Biodiesel in higher concentrations tends to gunk up the valves in such a system. The solution is to inject the fuel directly into the exhaust, which adds parts and cost, but some do this.

There still maybe an issue with common rail and biodiesel.

[papajack]

Originally Posted by shatto

Have you been using it long enough to know the maintenance aspects?

The maintenance is higher on these cars. The transmission alone requires a maintenance every 40K miles, that is several hundred dollars.

[jack0351]

As an owner of a Ram 3500 with the DEF, I can say that I get much better fuel economy than I did on the truck that it replaced. The F450 I had before this got an average of 12mpg on my daily drive, and I was doing my damndest to get good mileage (driving 55 on the highway, etc) The Ram gets 15mpg at 65/70 on the same route. So roughly a 25% increase in mileage, or more once you consider the speed increase as well.

DEF is available at the pump at truck stops for $2.79/gal which brings your cost down to below a penny per mile. Although you would look "funny" pulling into a big rig pump with a passenger car, I would do it for the savings.

I haven't gotten into the maintenance as much yet, as I only have 25K on my truck, but a LOT of the newer vehicles are going for transmission service earlier in the lifecycle. Where the service interval used to be 50K+miles, it is now down to 30K miles. I don't equate that to the DEF, unless the diesel transmission needs the service and the same transmission on a gas engine doesn't.

[trollbait]

What size is the DEF tank, and how often do you have to fill it?

I've figured a gallon of DEF is used per 1000mi. If true, then filling with the box available at stores would cost under half a cent per mile. That's paying $4.80 to $5 per gallon for the DEF.

[jack0351]

My DEF tank is 5.5 gallons, and I fill it roughly once every 3-4 months.

Your calculations are about right for the DEF usage. 1000miles/gallon is a pretty good rule of thumb. A nice things about my truck, and I assume the others, is that there is a DEF guage as well as a digital warning when you get to either 350 or 500 miles remaining. I'm not certain about it, as anytime it gets to 1/4 tank, I swing by the truck stop by my wife's work.

I was keeping a jug of DEF in the truck, but it uses so little normally that it's not really worth keeping a jug of it around. Plus the shelf life goes down if you expose it to high heat.

[sparkn]

It isn't the DEF that's causing fuel mileage problems. It's the DPF filter. A DPF adds exhaust restriction and a regeneration is 100% wasted fuel. The DEF is used to make Nox removal more efficient in the SCR so manufacturers have more breathing room (pun intended) to produce more power AND efficiency. The Jetta mentioned above will have more HP and fuel mileage in 2015 when it gets DEF added along with moving the SCR and DPF closer to the engine to minimize regen cycles.