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2012 Volkswagen Passat Twelve Month Test - Month 8

January 2013: Ad What?


AdBlue warning screen

AdBlue warning screen

Photo © Aaron Gold

January started out with a trip to see my folks -- me, my wife Robin, the kids, the dog, and a trunk stuffed to the gills (and with 15.9 cubic feet of cargo space, believe you me, that ain't easy). I expected the extra weight to take its toll, but the Passat's diesel engine seemed unaffected by the load -- it was just as quick up the steep grades in eastern California, and our fuel economy only was only a couple of MPG less than what I'm used to seeing on long trips.

Later in the month, Robin came home to tell me the car was nagging her. "There's a message on the screen," she said. "Something about AdBlue, and how it's not going to start in 500 miles. You should probably check it out as part of your husbandly duties." So I dutifully went out to the Passat, turned the key, and saw the message in the photo: "Top up AdBlue! No engine start possible in 550 miles."

What is AdBlue?

For those unfamiliar, AdBlue is a trade name for diesel exhaust fluid (DEF), part of the Passat TDI's emissions system. Modern diesels are tuned to reduce soot and unburned fuel in the exhaust, but this increases the amount of nitrogen oxides (NOx) in the exhaust. To solve this problem, DEF -- a mix of urea and deionized water -- is injected into the exhaust just upstream of the catalytic converter. The converter heats the fluid, causing it to vaporize and decompose into ammonia and carbon dioxide. The ammonia reacts with the NOx, producing water and nitrogen in its place.

The whole system is known as Selective Catalytic Reduction, or SCR, and it falls under the Fed's emissions laws. While the engine can run just fine without AdBlue, the law says it may not -- so if the car runs out of fluid, the engine will not start. That explains the warning message, which starts appearing around 600 miles before the AdBlue tank runs dry.

The Passat TDI has a 5 gallon AdBlue tank which is accessed through the trunk. Five gallons is supposed to last 15,000 miles, give or take, and the level is supposed to be checked as part of the 10,000 mile service, which we had done in October. I asked about the fluid at the time, and the dealership said the level was fine, and that if it ran low we'd be covered under the free maintenance program. Looking back, I don't think this is entirely correct; they should have topped off the tank at 10,000 miles. (I'll cut them a break, since SCR is fairly new to VW; only the Touareg and Passat TDI use it, while the more popular Jetta, Golf and Beetle diesels do not.) Regardless, it wasn't until well after 19,000 miles that our Passat began to run low on AdBlue. I took our Passat back to Van Nuys VW, and true to their word, they topped off the tank at no charge to me.

What does the future hold?

So what happens when the Passat goes past the 3 year/36,000 mile free service program? I called around to a couple of Volkswagen dealerships and was quoted $13.25 for a 1 gallon bottle of AdBlue and $20.25 for a 2.5 gallon bottle, plus anywhere from $36 to $55 in labor to pour it into the tank. (Seriously?) A little searching online found several auto parts stores selling 1 gallon bottles for $8 and 2.5 gallon bottles for $15. VW's 1-gallon bottle does have a nifty no-spill nozzle (the 2.5 gallon doesn't), but it looks like a funnel and a steady hand will work just as well. Personally, I'd go the DIY route.

The idea of disabling the car if the AdBlue fluid runs low does irk me a bit. While I don't anticipate a shortage -- heavy-duty trucks built after 2010 use SCR as well, as do diesel cars from other manufacturers -- there is always the question of price fluctuations. And what happens when the technology becomes obsolete? Honda's i-DTEC diesel engine (which they talked about putting in Acura products, though that idea has since been shelved) is able to produce ammonia for SCR directly from the combustion process, eliminating the need for DEF. Diesel engines have an exceptionally long life, so this is something long-term Passat TDI owners should be concerned about -- I can't help but wonder what will happen twenty or thirty years from now.

Other matters: Better MPG, no more coolant loss

AdBlue aside, we put a lot of miles on the Passat this month, only partly due to a Las Vegas road trip with friends. Here the big back seat came in handy; no one ever seems to complain when we take our car. It's the roomiest and cheapest way to travel. Most of the driving was our usual around-LA routine, and I noticed that our daily-driving MPG seems to have crept up by about 1 MPG. We're now averaging 41 MPG even which, as I mentioned last month, is well in excess of the 34 MPG combined figure predicted by the EPA. As for the coolant loss I wrote about in the October update, after 10,000 miles it has not returned. And that reminds me -- it's time for the 20,000 mile service. How time flies!

Next: February 2013 update: Is this thing ever going to break?
Previous: December 2012 update: Diesel economics
Test index

January 2013 summary:

Starting mileage: 17,166
Ending mileage: 20,214
Mileage this month: 3047.8
Average fuel economy this month: 40.7 MPG
Average fuel economy overall: 41.0 MPG
Repair/service costs this month: $0
Total repair/service costs: $0
Problems observed this month: AdBlue fluid low

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