I don't know if it's a liability issue or not, but I wouldn't think it would be since the filters generally work as stated. K&N does have a rather extensive warranty that extends out to the repair of any engine or engine part that is determined to be a direct result of the K&N filter. I don't know if anyone has taken advantage of that or not, but I do know that when you need to replace a Mass Airflow Sensor under warranty, Daimler will not honor the warranty if there is a K&N filter installed. K&N also makes it very clear that the filter needs to be very, very, very properly serviced and oiled up juuuust right or their warranty becomes void.
Several people have had to replace the Mass Airflow Sensor (MAF) in their Sprinter because of the oil and the silica grit that gets accumulated there which renders the MAF dead. I know three personally who were using K&N filters in their Sprinters who had this happen to them. One was still under warranty, which Dailmer did not honor because of the K&N filter. Was the MAF damaged by the filter, or just worn out? Hard to say. But it usually happens within weeks of installing the K&N filter.
It takes a little longer for the turbo to sandblast the turbo vanes and engine, but even at that an oil analysis will quickly tell you what it happening when the results invariably show a dramatic increase in wear metals. It would be hard to definitely pin that on the K&N filter.
With any diesel in general, but with a turbo diesel especially, clean air is critical, and the K&N's simply don't filter the air all that well. They let large volumes of air through that will increase horsepower, but that's really more for gas engines than with turbo diesels that have Mass Airflow Sensors that are tied to air intake temp sensors and turbochargers and intercoolers and EGR valves and ECU's and everything else that scales up or down in response to more or less airflow. So the increased airflow of the K&N (of which there really isn't any) ends up being negated by the signals sent to the computer by the sensors, anyway.
It's like the guy who swore up and down he could modify his Sprinter with a "warm air intake" which would give him more power and better fuel mileage, not realizing that the warmer air gets compensated for by the air intake temp sensor and the MAF and the intercooler. Or those Sprinter owners who will idle when it's really, really hot and will pop the hood to keep the engine cool (like you would or any gasser), when in reality the temperature control system of the Sprinter will just compensate for that, too, and will operate at the temp it's supposed to, hood popped or not.
Basically, if you have a turbo diesel that employs a MAF, stay away from any oiled "performance" air filter. The stock air filters will outflow any performance filter, anyway.
Do some searches over at
TDIClub for more information and horror stories. It is a little harder doing a search for K&N because of the "&" so you have to get creative with the use if quotes and stuff, but here's a couple that will give you an idea.
Thoughts on K&N Air Filter - TDIClub Forums
K&N Air Filter for new 2009 TDI? - TDIClub Forums
K & N Air Filter - TDIClub Forums
It's a topic over there that really and truly has been beaten to death, perhaps hundreds of threads, all saying essentially the same thing, so finding a bunch of K&N Filter threads won't be a problem.
Best "recap" from the site:
-No appreciable power improvement (dino tested)
-Less filtering capability
-Causes MAF failure
-Many have reported bad seal with the airbox. (Bad seal=driving with no filter...
)
Best signature line:
Friends don't let friends buy K&N Air Filters
