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I keep reading a tremendous of unscientific nonsense when it comes to engine failures. That is the nature of the internet but somehow I am still surprised by it.
The biggest piece of nonsense put out is a general lack of understanding of what system failures are. The laws of physics don't change from one car to another. If a part is going to fail under a given set of circumstances in one car, it will fail in every car where those circumstances exist. God may play dice at the quantum level but he doesn't play dice at the systems engineering level. If say the IMS bearing lasts 150,000 miles in one engine and blows up at 5,000 miles in another car, there is something different going on in the second car; either the part was defective or something was different in the way the car was used or maintained to make the part fail. Parts don't fail under identical conditions some percentage of the time. They fail in general use some percentage of the time because those are the instances where they are subjected to the conditions that make them fail. It is a subtle distinction but an important one.
I constantly read anecdotes and crackpot theories put out by people who claim to know better regarding the IMS issue or cylinder scoring that make absolutely no sense because there are thousands of counter examples that disprove the theory. If infrequent use caused IMS to fail, they would fail in every car that had infrequent use, not just some of them. If driving and storing the car in cold weather caused the engine to score, it would happen to every car under those circumstances. If not, there is something else going on causing the scoring. Correlation not only doesn't necessarily equal causality, it can disprove causality if there are counter examples.
With this in mind, consider three things,
1. There has never been a systematic explanation of why IMS bearings fail. No one has ever pointed to a cause or a set of circumstances where the bearing predictably fails for a known reason. All they have is conjecture and anecdotes of which there are many more anecdotes that go the other way. Since 90% of the parts never failed, any anecdote saying the part failed for this reason can be disproved by ten anecdotes that show the part didn't fail under identical circumstances.
2. IF there was a systematic explanation and flaw in the part Porsche would have found it. Every 996 and 986 Boxster that had a blown IMS in the first years was covered under warranty. The engines were all taken back to Porsche and examined. If there was a systematic failure, either with the manufacture, design or use of the part, any competent engineer with access to all of the failed parts and engine would have found it.
3. We know Porsche didn't find such a flaw because if they had, they would have recalled the part and would have fixed it. The conspiracy theories about Porsche knowing about the design flaw and hiding it are ridiculous. Replacing the bearing is a $800 job. Porsche was on the hook for replacing every blown engine under warranty at a cost of over $20,000 an engine. If the engineering studies had shown a flaw in an $800 part that was going to cause the company to have to replace 10% or more of the tens of thousands of engines being sold, they would have recalled the part. It would have made no economic sense to do otherwise. The only reason they didn't recall the part was because the engineers were telling them there wasn't anything wrong with it. And don't tell me the engineers were playing CYA over a design flaw they were guilty of. The engineers who designed the M96 engine are not the only engineers at Porsche and any competent engineer could have looked at the data and seen a defect if there really was one. Why did they change the design of the part? Because they thought the new design was better. That does not however mean the earlier one was defective. If it had been, they would have recalled it to avoid paying the resulting warranty claims.
So what caused all of the IMS failures? There is one known way to kill an IMS every time, oil starvation. Oil is the one thing all of the cars that failed have in common and the one way we know the part will fail. On top of that, the two no kidding known engineering failures in the M96 engine relate to oil. The rear main seal was often defectively manufactured and was prone to failure causing oil leaks. The cylinder walls, if the block was not manufactured and pressed together under the exact right temperature, at the exact right pressure, would develop microscopic cracks that over time would expand into cylinder scoring which causes oil consumption. As a side note, don't believe anyone who tells you that the M96 engine has cylinder sleeves that fail, it doesn't have cylinder sleeves at all, or that it has Lokasil lined cylinder walls. Lokasil is a manufacturing process not a material. If anyone tells you otherwise, tell them to take some classes on metallurgy or welding and get back to you.
Remember two other things about the oil system of the car. First, the car has one of the most unreadable dipsticks known to mankind and is notorious for having squirrelly electrical systems. This means most people if they checked their oil at all relied on the dashboard electronic measurement, which is hardly bulletproof and is only accurate if the car is on very flat ground even if it is working. Second, the oil drain plug has a metal washer and seal and requires a torque wrench to properly tighten. Don't use a torque wrench and over tighten that thing and it will bend the washer and create a leak. I have never seen or heard of a car that required a specific torque for the oil drain plug. How many people do you think ignored that and over tightened it creating a leak? A few I am sure.
Put those defects together with the fact that Porsche sold the M96 engine in numbers unheard of by the company before then and you start to see what happened. Porsche used to sell only to enthusiasts. With the coming of the Boxster and the 996 it was for the first time selling in large numbers to non-enthusiasts. People who didn't know anything about cars. People who didn't check their oil. People who didn't change their oil at all or if they did did so based on mileage alone even if that meant leaving the same oil in the car for years on end. People who continued driving the car even though the warning lights were on.
In addition no customer will ever admit that they did something wrong. Everyone whose engine ever fell apart will swear on a stack of bibles they checked the oil every day and never saw it coming. The reality of course is usually much different.
Put it all together you can see what happened. People bought the cars, didn't check their oil or pay attention to the warning lights and were unlucky and had a small RMS leak or some cylinder scoring and were leaking and burning their oil away until finally they starved their engine of oil and the IMS failed. Others didn't change their oil and only drove the car once in a while and maybe had small leak they didn't notice and ended up driving on low oil that was too old to work well. Other people may have had a catastrophic RMS failure while driving, lost all of their oil, and been too dumb to immediately turn the engine off. Start adding those numbers up and you easily get to the number of failures. More importantly, you get failures that go across the wide range of mileage and use and conditions that occurred.
After nearly obsessing about this issue for a year and reading every single book I could find on the 996 and every internet forum posting available on the subject, I have come to the conclusion, there isn't anything wrong with the IMS bearings in these cars. What is wrong with these cars is that they are prone to oil leaks and oil consumption and if you don't pay attention to that the engine fails.
Your remarks are consistent with explanations given in the book "996 The Essential Companion." However attempts to discuss these issues on this forum are almost always met with hostility and ridicule. On the positive side you are far from alone in your point of view. Happy New Year.
1- The original IMSB is a sealed unit that is permanently lubricated. If the unit is operating correctly and has not been exposed to Stage 1 bearing failure (failure of the seal) the engine can run completely out of oil and seize, but the IMSB will remain flawless.
2- The factory repaired hundreds of engines in the 99 and early 2000 model year, and used a metal matrix composite sleeve to do so. These were engines that had previously failed QC, but had to be repaired to fill orders for cars as the casting factory at Kolbenschmidt had burned, leaving the factory without crankcases. Read about this in the August 2008 issue of Excellence Magazine, in the Tech Forum that was written by the late Jim Pasha. This article was the first to uncover the backstory on lots of failures.
The slipped sleeves became famous with these aforementioned engines that seldom made it out of warranty before the sleeve failed.
Here's a classic photo that shows the "sleeve" thats supposedly non- existent clearly.
The IMS will die without oil. The lack of oil effects the cam tensioners and that destroys the IMS.
As far as the sleeves go, I can only go by the design of the car. Even if there were "hundreds" BFD. The engine was made by the hundreds of thousands. The other 360 thousand or so engines don't have sleeves. And you showing me a picture of a slipped sleeve doesn't prove it had that sleeve when it left the factory. Any engine rebuild shop can bore and sleeve a cylinder and do it badly.
And the bottom line remains. no one has ever come up with an explanation for the IMS failures. That alone shows that something else is causing the failure. If it were the IMS, there would be a consistent reason why it was failing
1. You have now personally contributed to the misinformation you rant about
2. You have now been schooled on the IMSB and the factory cylinder sleeves
Originally Posted by JohnCK2014
I keep reading a tremendous of unscientific nonsense when it comes to engine failures. That is the nature of the internet but somehow I am still surprised by it.
Originally Posted by Flat6 Innovations
Two facts:
1- The original IMSB is a sealed unit that is permanently lubricated. If the unit is operating correctly and has not been exposed to Stage 1 bearing failure (failure of the seal) the engine can run completely out of oil and seize, but the IMSB will remain flawless.
2- The factory repaired hundreds of engines in the 99 and early 2000 model year, and used a metal matrix composite sleeve to do so. These were engines that had previously failed QC, but had to be repaired to fill orders for cars as the casting factory at Kolbenschmidt had burned, leaving the factory without crankcases. Read about this in the August 2008 issue of Excellence Magazine, in the Tech Forum that was written by the late Jim Pasha. This article was the first to uncover the backstory on lots of failures.
The slipped sleeves became famous with these aforementioned engines that seldom made it out of warranty before the sleeve failed.
Here's a classic photo that shows the "sleeve" thats supposedly non- existent clearly.
Who is more credible? A person "maybe an engineer" that has read every book and internet statement for over a year and come to the conclusion that low oil levels is the culprit. Someone that has spent years dealing with the failures and researching and fixing them with his own hands instead of internet or book theories. He posts pictures as proof of sleeves that don't exist and explains things he deals with for years on a daily basis. It is amazing to me to read the statement "there isn't anything wrong with the IMS bearings in these cars. What is wrong with these cars is that they are prone to oil leaks and oil consumption and if you don't pay attention to that the engine fails." If as John Ireland claims that the book "996 The Essential Companion" says the same thing I would be even more amazed and I doubt it does.
The IMS will die without oil. The lack of oil effects the cam tensioners and that destroys the IMS.
Ummn,
Whats a "cam tensioner"? Are you referring to chain tensioners? If so, they are oil pressure fed, but they take less than 6 PSI of oil pressure to fully tension the chains. Trust that if you are cruising down the highway and your oil pressure drops to a point that would make these tensioners no longer function, that you'd lose a rod or main bearing well before anything else.
When the chain tensioners lose oil pressure, they lose tension, this can certainly create a failed timing chain, or broken chain rail, but either of those would stand a better chance of occurring rather than a failed IMSB. If what you state is correct, we'd see signs of these failures along with the IMSB failures, but thats not the case. If we do see collateral damage, it is created by the failed IMSB in most every case. There are some instances where I'll see a compound failure, but they usually occur with sub systems that do not operate in unison. Further, a chain tensioner can completely fail and the engine still will not have a camshaft deviation thats enough to throw a CEL, which takes +/-14*.
As far as the sleeves go, I can only go by the design of the car. Even if there were "hundreds" BFD. The engine was made by the hundreds of thousands. The other 360 thousand or so engines don't have sleeves. And you showing me a picture of a slipped sleeve doesn't prove it had that sleeve when it left the factory. Any engine rebuild shop can bore and sleeve a cylinder and do it badly.
Please do your homework on this. You are completely off base. The engine that is pictured was a virgin engine, from a virgin one owner vehicle that was only driven 12,000 miles in 13 years. It had never been rebuilt, and had never been extracted from the car. Had that vehicle been driven more, the sleeve would have failed under warranty, like most all the others did. All you have to do is read the Tech Forum article, it was written by a long time M96 researcher and historian.
Cylinder failure due to a slipped sleeve is MOF#1, it was the failure that led Bruce Anderson to tell Charles and I that we needed to start developing these engines, as he was receiving dozens of letters per month about cylinder failures. Today we hardly ever see this, in fact the one that I posted in that set of photos is the last one that we've seen here.
And the bottom line remains. no one has ever come up with an explanation for the IMS failures. That alone shows that something else is causing the failure. If it were the IMS, there would be a consistent reason why it was failing
They are just smart enough not to post them.
Your statements aren't making sense. Have you disassembled an M96 engine to follow the flow path of the oil system? Sorry, the factory "layout" is a joke, and isn't accurate. Ever built one from scratch? Just curious where your first hand experiences that you are sharing here have come from.
John, there is so much stupid in your post it passed beyond funny.
Car manufactures much bigger than Porsche have been caught covering/ignoring issues much bigger than a little engine failure. Its a simple cost thing. If they analyzed the chance of failure that they would have to pay for was less than the cost of replacing all of the units, the car companies will go with replacing a few expensive engines every time. Same reason Toyota covered up their issues, Chevy, and plenty of other less recent examples. In cases like the 996, its not even a significant safety issue so they don't even have to worry about news reports about killer cars with nasty crash scenes.
While you are correct that there are high milage cars that have suffered IMSB failures, they are the rarity and do not disprove the accepted belief that low milage cars are more likely to fail. No one has claimed that 100% of low milage cars will fail or that high milage cars won't fail. Just that the former are more likely to fail.
The 996 is far from the only Porsche to suffer cylinder scoring either, but a common thread is that the majority of failures were found in cold climate cars. Again, not every cold climate car has the problem, but the numbers are significant enough to suggest there is a connection.
And calling the man that knows the most about the M96 outside of Porsche a liar (e.g. No proof the insert was factory) when he provides information about exactly where you can get more detail, pure class there mate.
I guess you are yet another internet moron that bought the car but didn't research it before hand and/or can't afford the associated risk. That is assuming you even own one...
Take the advise of those that have been there and those that actually know what their talking about. Learn how to take care of the car and get out and drive the hell out of it. You may have 500k miles or 5 before it dies because of the IMSB or (more likely) some idiot drunk t-bones you. Get out and enjoy every damn mile or sell it and don't look back. Those really are your only two options that will amount to anything worthwhile.
If there was a common theme why would someone not post this? Unless it's keeping people in business I'm not smart enough to figure this out I'm sorry.
Sitting on the fence about buying a 2000 6spd coupe with 87kms, the ims issue is the only thing putting me off. Don't care about the money if it pops, I care about getting stranded on side of the road with a pissed off wife waiting for a tow truck.
Sitting on the fence about buying a 2000 6spd coupe with 87kms, the ims issue is the only thing putting me off. Don't care about the money if it pops, I care about getting stranded on side of the road with a pissed off wife waiting for a tow truck.
Any 15 year old car has the potential to leave you stranded on the side of the road. Many with far worse odds that a 996 and regardless of how good of a PPI you get.
The best you can do if you pick one up is do any of the maintenance you don't have hard evidence was done, do the other preventative/proactive things that you may be concerned about, and then enjoy the car.
Worrying about how an old car may leave you stuck on the side of the road is just silly. If you can't handle that possibility then go get a new/CPO car that comes with road side assistance (because they can leave you stuck too).
I don't want to start an IMS thread to ask but since this thread has touched on it I'll try here.....
The thing touched on that I'm curious about is "higher mileage engines fail at a lower rate'.
My 2003 C4S is one of the IMSB types with the higher percentage of failure (@8%)
However, it is at 89,000 miles and well maintained by previous owner. Frequent oil changes at 6000 miles and oil analysis every change shows consistantly promising levels
Is there enough data on the rate of failure of high mileage vs low mileage of my bearing type to where you guys would expect the potential for IMSB failure in my high mileage engine is below the 8%?
Jake, the photo catching the sleeve issue in progress is amazing. Don't worry about the OP. I doubt he changes an air filter much less assembles engines.
Is there enough data on the rate of failure of high mileage vs low mileage of my bearing type to where you guys would expect the potential for IMSB failure in my high mileage engine is below the 8%?
With your mileage, why not just change the IMSB with your clutch change (assuming your on the original clutch)?
12-29-2014, 12:26 AM
Engine failures
