Clean diesel cars


I see stories about new clean diesel cars coming into the U.S. some time in 2009. VW, Subaru, Honda in the affordable range. The MPG estimates were, as I recall, in the 40s on the highway. Anyone have any more information on these cars and whether they’d be worth trying–even in their first model year?


Remember that “the first model year” of a car for those of us in the US is almost always year two or year three for most Japanese cars, due to the fact that they are introduced in Japan (and frequently in Europe) a year or two before those models arrive on our shores.

Right now, the Europeans are, in essence, being the guinea pigs for the new clean diesel cars that we will get in 2009-2010. In Europe, Subaru claims a 1000 km. cruising range for a turbo-diesel Outback, which, by my calculations would equate to mileage of at least 37 mpg. Some Subaru owners have reported mileage in the 50 mpg range, as have owners of diesel Accords.

If you want to see a website specifically for the new Subaru turbo-diesel engine, go to:

Also, if you go to the Subaru UK website, you can read comments from the British motoring press on the new diesel engine. I have to say that I can’t recall ever having read such overwhelmingly positive reviews.

Take a look at:

Also, to see an article about the new 62 MPG diesel Ford that will be sold only in Europe, go to:


The new clean diesels coming to this country will have to meet the requirements for both the EPA and CARB. This means they will be required to be equipped with exhaust after-treatment components to remove particulate matter (soot) and NOx. To remove soot each vehicle will have a Diesel Particulate Filter (DPF), and to reduce NOx a Selective Catalyst Reduction system (SCR).

The DPF accumulates soot in it’s ceramic media. As the soot accumulates, the exhaust gas temperature reaches a certain point where it ignites this soot where it burns and turns to ash. This is done because if the soot remained in the DPF it would take no time for it to become restrictive and cause excessive back-pressure. Ash is less restrictive than soot. But even with this, eventually the ash will accumulate in the DPF to a point where it will become too restrictive. When this happens, the DPF will either require replacing or cleaning. And either isn’t cheap.

The SCR system utilizes a specially treated catalytic converter where when urea is introduced, it reacts with the catalyst converting it to amonia. This amonia then reacts with the NOx converting it to nitrogen and water. So the vehicle will have an urea container that will require replenishment on occation. There are rumors in the industry that when more and more of these diesel vehicles hit the American roads, the price of urea is going to increase because of demand. Right now we pay fifty cents per gallon of urea. But this could go as high as $3.00 per gallon of urea.

So with the new cleaner diesel vehicles, not only do you have the high cost of diesel fuel, but now you’ll have urea at it’s price, and a DPF the will evetually require replacement at a substantial cost. For these reasons, I would wait a few years to see how cost effective these cleaner diesels are truely going to be.



“So with the new cleaner diesel vehicles, not only do you have the high cost of diesel fuel, but now you’ll have urea at it’s price, and a DPF the will evetually require replacement at a substantial cost.”

Talk to Craig about a used 300D.


in the 40s on the highway.

That would be on the low side.


LOL, mine are not for sale.

The “new” benz diesels and VW TDIs have both been around for a few years, if you want a “clean diesel” now. Otherwise I expect there will be more choices in a couple of years. With the current emissions requirements, the newer ones will probably be more expensive than their gasoline equivalents (benz has them priced about the same, but I think that’s a marketing decision).


I recall reading that the Mercedes Benz Clean Diesel technology utilizes a urea tank, but that Honda’s technology does not require the use of urea. If this is true, that gives Honda (and any other company that uses a Honda-like system) an incredible marketing edge.


Honda must be aware that many people will avoid maintaining these systems, just as they avoid maintaining the systems now in use…until the vehicle doesn’t run any more. That would be one reason for them to design a system to go around (obviate the need for) such routine maintenance.
The same things which are ignored in an old technology, will be ignored (as long as possible) in a new technology.


My understanding is that the feds have required an interlock that will prevent the engines from starting after the urea tank is exhausted, I believe it will count down the remaining starts until the vehicle is disabled if the system isn’t serviced. I think the point of the urea system is to maintain reasonable mileage/performance while meeting NOX requirements. I don’t know what the maintenance interval will be, but I believe it’s supposed to correspond to either the A or B service interval to avoid extra services. It will be interesting to see if someone gets a non-urea system certified in the U.S. and what kind of performance they can achieve.


Non-urea NOx catalyst systems are widely used on “clean” diesel cars. However, the majority of clean diesels that will be sold in this country will use urea. The reason is that the non-urea systems are not capable of handling large amounts of exhaust gases (and large amounts of NOx). Therefore, they’re only used in small diesel cars. If the engine is much bigger than 2.0L or if the car is much heavier than about 3,000lbs, than be rest assured the engine will use a urea system. Since we like our cars big and powerful we’ll be stuck using urea if we choose to drive a clean diesel.

From what I’ve read about the the MB “Blutec” diesels, expect the urea tank to only need refilling about every 10K miles. It will normally be topped off during an oil change.
It will give you a warning when there’s about 1,000 miles of urea left. This gives the procrastinator plenty of time to get the tank refilled. And yes, I’ve heard of the urea interlock too. If the urea tank runs dry or is refilled with anything other than urea, the engine’s computer will take notice. The car will run fine until you go to restart it. That’s when you’ll have to get it towed to the dealer.