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How do you view the results? When I click the original link, it only wants to give me the survey again.
Good question - and I'm unsure of the answer. I can see the results as the creator of the survey. I think I may have to close it to make the survey public, but before I do that, I want to see if there is another way..
Found out how to do it - but it requires that the creator (who is someone besides me, I just edited and put it together) - make it viewable. I've asked for that to happen and will post a link for it as soon as it is.
So the only 100% certainty in these results is that you should modify your Cayenne, which will prevent the problem from occurring, as 100% of reported failures resulted on non-modified engines.
Guess I'm all set.
Kidding of course, but interesting that only 13 people answered that question for some reason.
Here is my sticker.
2008 CTT. Build date 6/07
56,000 miles currently with no issues. Using Mobil 1 0w 40 "European Formula" with Lucas Synthetic oil additive.
Missing is the location of owner/vehicle - since I believe that climate is the main factor that causes these failures it is important. I know of 2 more failures in my town from just the last 6 months. Cars that do not get freezing temps will likely not see this.
Missing is the location of owner/vehicle - since I believe that climate is the main factor that causes these failures it is important. I know of 2 more failures in my town from just the last 6 months. Cars that do not get freezing temps will likely not see this.
Good data, and yes that fits with the common understanding of these failures. Having location in the dataset would be good, to the extent that the car's location history is known. BTW, mine is zip 94065.
But as a counterpoint, I'll say that 100% of my Cayennes (one, a 2004 S) have had the bore scoring problem, and I am in the SF Bay Area (and the car has lived here since new) where we hit freezing about once per year. So from my sample, 100% of the non-freezing cars have scored. Maybe I should follow Petza914's advice and modify the engine, since 100 * 0 = 0.
I'm still not convinced the issue is one of improper tolerances from the factory. It makes no sense.
If the bore scoring, as it relates to tight tolerances, was a thing from birth of an engine, damage would happen immediately, when intolerances at their tightest. Not 50-90k miles down the road when everything is essentially much "looser."
There is another factor that's being overlooked.
In the 928 world, catastrophic engine failure was happening to engines attached to automatic transmissions. Failure was happening around the same time as the Cayenne .
High flex plate load was the cause of the failures.
As a clueless engineer who has yet to have to do a post mortem on a bore scored 4.8 engine (crosses fingers at 161K miles). The failure mode appears as bore scoring followed by rod knock and if not fixed with in a few hundred miles with a rebuild / new engine is a rod through the block. I have noticed that people hear their engines valve lifters getting louder as time goes on which is common on direct fuel injected engines as in the cayenne. I propose the wear is not from bad fitment of the pistons to the cylinder but of a valve lifter wearing out causing complete engine failure. The failure mode that requires the least assumptions given the mean time to failure in this survey (beyond owners lying about oil changes) is carbon buildup on the intake valves causes dragging on a tippet releasing particulate into the oil which catches on a piston ring causing galling on the mirror polished cylinder walls. this would cause rapid deterioration of engine health. I vehemently disagree with the idea that tight tolerances alone are responsible for the bore scoring issue on the 957 4.8L engines. If cold temps and tight tolerances alone were responsible for the issue the all northern living cayennes should have died within a year or three. I propose the actual failure path on these engines is a valve lifter wearing out letting aluminium into the oil the aluminium particulate gets between the cylinder wall and mirror polished cylinder galling the cylinder wall causing an exponential reaction resulting in the failure of the engine. I may be crazy but this is the most rational explanation i can derive. let me know what you think.
As a clueless engineer who has yet to have to do a post mortem on a bore scored 4.8 engine (crosses fingers at 161K miles). The failure mode appears as bore scoring followed by rod knock and if not fixed with in a few hundred miles with a rebuild / new engine is a rod through the block. I have noticed that people hear their engines valve lifters getting louder as time goes on which is common on direct fuel injected engines as in the cayenne. I propose the wear is not from bad fitment of the pistons to the cylinder but of a valve lifter wearing out causing complete engine failure. The failure mode that requires the least assumptions given the mean time to failure in this survey (beyond owners lying about oil changes) is carbon buildup on the intake valves causes dragging on a tippet releasing particulate into the oil which catches on a piston ring causing galling on the mirror polished cylinder walls. this would cause rapid deterioration of engine health. I vehemently disagree with the idea that tight tolerances alone are responsible for the bore scoring issue on the 957 4.8L engines. If cold temps and tight tolerances alone were responsible for the issue the all northern living cayennes should have died within a year or three. I propose the actual failure path on these engines is a valve lifter wearing out letting aluminium into the oil the aluminium particulate gets between the cylinder wall and mirror polished cylinder galling the cylinder wall causing an exponential reaction resulting in the failure of the engine. I may be crazy but this is the most rational explanation i can derive. let me know what you think.
The carbon or aluminum theory certainly sounds plausible. I wonder if any of the scored motor owners ran regular UOA on their oil changes and if they say any elevated aluminum readings prior to the noise that meant the bores were scored. If so, elevated aluminum readings could trigger a boroscope and maybe the heads could be rebuilt before the aluminum scores the cylinders. Alternatively, maybe once the elevated aluminum is there, its too late already and the damage is done and unpreventable.
It looks like in the Porsche DFI motors that the injector pulse might actually wash the back of the intake valves, and be the reason that our motors don't build up carbon on the intake valves the same way BMWs and other DFI motors do, requiring a decarbon treatment in as few as 35,000-50,000 miles.
For any of the 08 owners with scored bores, what did the carbon buildup on the intake valves look like when the motors were torn down?
As a clueless engineer who has yet to have to do a post mortem on a bore scored 4.8 engine (crosses fingers at 161K miles). The failure mode appears as bore scoring followed by rod knock and if not fixed with in a few hundred miles with a rebuild / new engine is a rod through the block. I have noticed that people hear their engines valve lifters getting louder as time goes on which is common on direct fuel injected engines as in the cayenne. I propose the wear is not from bad fitment of the pistons to the cylinder but of a valve lifter wearing out causing complete engine failure. The failure mode that requires the least assumptions given the mean time to failure in this survey (beyond owners lying about oil changes) is carbon buildup on the intake valves causes dragging on a tippet releasing particulate into the oil which catches on a piston ring causing galling on the mirror polished cylinder walls. this would cause rapid deterioration of engine health. I vehemently disagree with the idea that tight tolerances alone are responsible for the bore scoring issue on the 957 4.8L engines. If cold temps and tight tolerances alone were responsible for the issue the all northern living cayennes should have died within a year or three. I propose the actual failure path on these engines is a valve lifter wearing out letting aluminium into the oil the aluminium particulate gets between the cylinder wall and mirror polished cylinder galling the cylinder wall causing an exponential reaction resulting in the failure of the engine. I may be crazy but this is the most rational explanation i can derive. let me know what you think.
I think you are completely wrong. The cause is improper clearances due to mistakes made by different subcontractors that did finishing operations on the blocks. Hence why some fail and some do not. The walls are not mirror smooth or even close. The pistons are a lot softer than the block and use some type of iron ferrite coating on the skirts to prevent galling. Once that is gone due to improper clearances its game over. Same as when you build an engine, have the pistons coated, and do not take into account the coating thickness in the final bore clearance. They end up too tight because you finish the bores for uncoated pistons and the coating wears off. The coating is meant to be sacrificial in extreme conditions and not a daily wear item.
The carbon or aluminum theory certainly sounds plausible. I wonder if any of the scored motor owners ran regular UOA on their oil changes and if they say any elevated aluminum readings prior to the noise that meant the bores were scored. If so, elevated aluminum readings could trigger a boroscope and maybe the heads could be rebuilt before the aluminum scores the cylinders. Alternatively, maybe once the elevated aluminum is there, its too late already and the damage is done and unpreventable.
It looks like in the Porsche DFI motors that the injector pulse might actually wash the back of the intake valves, and be the reason that our motors don't build up carbon on the intake valves the same way BMWs and other DFI motors do, requiring a decarbon treatment in as few as 35,000-50,000 miles.
For any of the 08 owners with scored bores, what did the carbon buildup on the intake valves look like when the motors were torn down?
It is a direct injection which means it go's directly into the cylinder. The backsides coke because of cam overlap and raw fuel being pushed back into the port on the bottom of the compression stroke.
I propose the actual failure path on these engines is a valve lifter wearing out letting aluminium into the oil the aluminium particulate gets between the cylinder wall and mirror polished cylinder galling the cylinder wall causing an exponential reaction resulting in the failure of the engine. I may be crazy but this is the most rational explanation i can derive. let me know what you think.
Why would you think a valve lifter is made from aluminum? The cylinder walls are not "mirror polished" - and the failure is fairly common on a certain cylinder (#5) of the V8 engines - something that wouldn't happen if the oil was contaminated. I can't argue with "I may be crazy"..
Just thought I'd distill down some of the results from the bore scoring survey.. and this is the record of reported failures:
I find it interesting that there were only 3 failures reported occurring before 60,000 miles (and out of those, only 1 before 30,000 miles.) The survey results included 168 vehicles - 23 reported failures (13.7%) The failures were almost equally distributed between normally aspirated and turbo engines (putting to bed the theory that turbos were less prone to failure due to the under-piston oil squirters.)
12-16-2018, 03:16 PM
