Potential Cause of a Cracked DPF

TurboDieselPoint · Nov 6, 2014

It seems cracked DPFs are a growing issue with the CBEA and CJAA. The conclusion most people jump to is that they are cracking due thermal stresses from hot shutdowns or are failing due to manufacturing defects, but I thought of another cause that might be the source of trouble for those with cracked DPFs.

Could these drivers be cracking their DPFs when they run over potholes or other imperfections in the road's surface that would cause a shocking jolt to the rest of the vehicle? I'm not suggesting the DPF is hitting anything, but rather the bone-jarring shock from a high-speed encounter with a pothole would simply fracture the ceramic "honeycomb" inside the DPF.

Discuss.

PlaneCrazy · Nov 6, 2014

I wasn't aware of this issue, so have nothing to contribute, but am interested in what others have to say.

OilBurningBrit · Nov 6, 2014

I'm interested too, but was thinking more along the lines of a connection to the iced intercooler syndrome than an impact. Seems like pumping water vapor through the DPF could be damaging.

jav · Nov 6, 2014

Mine was involved in a front end collision and was declared a total loss even though there was no engine damage, no air bags deployed, didn't not even the hole radiator or ac condenser BUT- I fixed it and I now have a cracked DPF. I always assumed it was due to regens but I wonder if the collision could have caused it?

questman · Nov 6, 2014

I believe that as the DPF is an automotive part designed to be attached to an exhaust system on a moving vehicle there would have been some impact testing done on it. It seems the technology is on one hand advanced, the other hand a primitive can. Some DPF's have failed early, been replaced, failed again. I suggest manufacturing defects. A light bulb operates many years on a car. We've had 100 years to perfect it. The DPF is fairly new tech, VW makes them to spec as engineered, however, reliability is a crap shoot without long term testing and experience.

TurboDieselPoint · Nov 6, 2014

questman said:
I believe that as the DPF is an automotive part designed to be attached to an exhaust system on a moving vehicle there would have been some impact testing done on it.

I would think (and hope) so, but we don't know for sure if VW did. Assuming they did test it, we don't know what the threshold for damage they found was.

questman said:
It seems the technology is on one hand advanced, the other hand a primitive can. Some DPF's have failed early, been replaced, failed again. I suggest manufacturing defects. A light bulb operates many years on a car. We've had 100 years to perfect it. The DPF is fairly new tech, VW makes them to spec as engineered, however, reliability is a crap shoot without long term testing and experience.

I understand that you think manufacturing is the problem, but I fail to see the logic of your argument. Are you trying to suggest that the cracked DPFs had structural shortcomings due to lack of long-term engineering and development, unlike the lightbulb, a shock sensitive component, which has been around long enough to be reliably applied to cars? This seems to support the idea that manufacturing discrepancies are not the culprit, but rather that the DPFs simply have a fragile design.

Respectfully, I'm not trying to argue with you. I'm just confused and want some clarification.

questman · Nov 6, 2014

I’m thinking along the lines of the overall design and testing of the DPF. VW put together a system to pass emissions, an obviously complex system. I believe the impact issue is the least of the worries. With the light bulb analogy I was suggesting previous experience and knowledge relating to perfecting a part riding on a car. I believe VW would have understood possible impact and shock stresses perfectly well but it seems to me they never fully anticipated the thermal issues. If they suggest checking the DPF at 120,000 miles then obviously they believed at rollout time they had a long-lasting part and yet still so many early failures. A bad batch? If the DPF cost VW $200 to make and it’s made to spec and it fails early then it should have cost $400. I’m suggesting a manufacturing flaw, yes, however, also an engineering flaw but in the area of thermal not impact. They failed to overbuild a part-thought it was good enough. Then there are those still driving with the original DPF on their cars at 150,000 +.

Regardless, it’s an interesting thread you started T_D_P.

TurboDieselPoint · Nov 6, 2014

questman said:
I’m thinking along the lines of the overall design and testing of the DPF. VW put together a system to pass emissions, an obviously complex system. I believe the impact issue is the least of the worries. With the light bulb analogy I was suggesting previous experience and knowledge relating to perfecting a part riding on a car. I believe VW would have understood possible impact and shock stresses perfectly well but it seems to me they never fully anticipated the thermal issues. If they suggest checking the DPF at 120,000 miles then obviously they believed at rollout time they had a long-lasting part and yet still so many early failures. A bad batch? If the DPF cost VW $200 to make and it’s made to spec and it fails early then it should have cost $400. I’m suggesting a manufacturing flaw, yes, however, also an engineering flaw but in the area of thermal not impact. They failed to overbuild a part-thought it was good enough. Then there are those still driving with the original DPF on their cars at 150,000 +.

Regardless, it’s an interesting thread you started T_D_P.

I see what you meant. I'm just curious why you had ruled out impact as the cause and instead think thermal stresses cause DPF failure. If anything, I think VW's misprediction would be the other way around. They well know the temperatures of regeneration and specifically designed the ceramic filter to withstand it, but I'm not entirely sure if they fully accounted for impact shock when they designed and tested the unit. Just my humble opinion.

TurboDieselPoint

ValveCoverGasket · Nov 7, 2014

questman said:
Some DPF's have failed early, been replaced, failed again. I suggest manufacturing defects.

The DPF is fairly new tech, VW makes them to spec as engineered, however, reliability is a crap shoot without long term testing and experience.

i would be willing to bet that the cars that have had repeated dpf failures are due to either drive cycle, or the engine not running right (but still within the bands of the obd faults, so as to not set any faults) causing increased loading/frequency of regens, or some combination of the two.

questman · Nov 7, 2014

It's obviously a combination of many factors and variables-no smoking gun. I wouldn't rule out any possibility due to the many different scenarios playing out; long lifespan, short lifespan, highway, city, cold climate, hot climate. This thread is discussing a potential cause of a cracked DPF and it certainly could be impact. Perhaps a definitive cause will be discovered but as of now it seems that almost any suggestion should be left on the table.

ValveCoverGasket · Nov 7, 2014

TurboDieselPoint said:
I would think (and hope) so, but we don't know for sure if VW did. Assuming they did test it, we don't know what the threshold for damage they found was.

im certain it was run over 100s of thousands of miles of varying road surfaces.

ive not seen a dpf (speaking generally, as i dont work specifically with passenger cars) fail due to stress encountered via road conditions.

think about how hard youd have to strike something with your wheels in order to pass through a sharp enough jolt to the exhaust system (which is isolated from the road by the tires, the suspension, and the engine mounts) to cause damage.
color me highly skeptical.

piotrsko · Nov 7, 2014

My vote is for water inclusion. Either as ice expansion or steam. There's water there as a byproduct, but hard to see how the steam pressure can get that high, or maybe it doesnt have to. Perhaps water on a heated substrate causing thermal cracking . Not enough consistent data to map a failure mode.

Potential Cause of a Cracked DPF

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