Trying to stir it up again are we?

Thanks for that useful and informed contribution...

To save you reading all of it (as you obviously haven't) we appear to have surmised that a proportion of 996 and 997 engines have suffered catastrophic failure of IMS or cracked cylinders/heads. We cannot possibly determine the proportion from such a thread, as mostly only people with failures have posted and this is a very small proportion of all 996s built.

Baz, at Hartech, has explained the reasons for the failure and highlighted some more cost effective solutions to the new engine that always seems to be fitted when an OPC gets involved.

The other couple of hundred posts are mostly from an idiot called bcnrml trying to make a mountain out of a molehill and discredit Porsche, all its Agents and anyone who sells or maintains cars in the UK - for reasons yet to be explained, but favourites range from some form of commercial agenda, through revenge for OPCs failing to bow down and scrape to him, to being a sad person with nothing better to do with his life.

Cool... sorry for my slightly stroppy reply - thought you had been sent along by 'you know who' as it had all gone quiet for a few days...

Have posted here with my high mileage 2001 C4: just did the clutch at 95,000 miles and at the same time had the Intermediate Shaft Bearing Assembly removed and replaced with the Inengineering upgraded assembly. My version of the 2001 had the double race bearing assembly. When removed and inspected, it was reported to me that it was in "perfect" condition. I replaced it anyway. The shop that did the work said that its experience has been that the double race version rarely fails as it gives a loud rattling sound that predicts failure. I was told that the more recent single race version give no warning and causes much of the trouble we read about. At the same time, I replaced the RMS with the 997 version as it allegedly is failure proof. At the same time I replaced the 996 shift assembly and cables with 997 parts; what a difference that made. Now my shift points feel like they are going into a gate and there is NO slop or searching for the middle gears. It feels much better and is shorter throw to boot. The 95.000 mile C4 drives like it did when it had 20K well broken in miles. I intend to drive it for another 50,000 miles. I have an Inengineering 160 degree thermostat and a standard oil filter adaptor and magnetic oil plug yet to install. I will also install an after market electronic regulator for the C4s two fans - the one recommended by Inengineering that uses the Porsche's existing heat sensor. It is user programable - I indent to turn on the fans at a lower temperature and to turn on the high speed at a lower temperature than the DME allows. I also will program it to cause the fans to operate after the ignition is turned off until the temp sensor reads 180 degrees. It is a good idea if one is trapped in summer traffic jams at low stop and start speeds, which is my commutation fate. Thats it. I believe that the combination of the things that I am doing, together with 5,000 mile oil changes and the use of a higher flow, better oil filter than stock will allow me to reach very high mileage without blowing the engine. My motoring is done in Westchester County of New York State and I commute over two hours round trip on highways. The only controversial part of my strategy is the 160 degree thermostat. I will save the stock one just in case. My point in posting in this thread a number of times is that with some luck, one can drive a stock 996 for high mileage without disaster - but, it requires very frequent use and a lot of highway miles. I understand that heavy use plus frequent oil changes are the trick. If I stored mine in the Winter (I commute with it all Winter) and used it only on summer, dry weekends, I would not have the same story to tell you. George C. McKinnis

I don't see any discrepency between reports. IMS bearings (if the tolerances allow them to last past the early mileages) wear the seal so it no longer acts as a seal and allows oil to enter and exit the bearing after which it seems to last forever (as previously reported by me - "APR"). Single row bearings actually have more potential according to the spec books than the double row equivalent APR

The problems of composites under creep are less well researched but it is clear that it depends on temperature changes, frequency and loads APR.

All engines we have measured (over 100) have some ovality and creep and many also have ovality up to 10 thou (0.25mm) after which they start to fail. It may be that careful warming up and long journeys reduce the influence and allow less ceep while harsh driving and frequent journeys (as largely undertaken in the UK) may result in shorter life. Prolonged warming up - once again - proposed as a good idea by us and others APR.

Again - APR - higher mileage engines seem to perform better than their older counterparts up and until they fail.

There will always be exceptions and for every engine that has lasted 150K there is another one like the one we are fixing this week that lasted 25K - what can you make of that as a rule or for advice to owners.

All we do is report on what we find, try to explain it and fix it and prevent a re-occurence (very succesfully to date) and nothing in the recent postings contradicts anything preceeding it from us.


Baz

Regarding my above entry discussing single vs. double race intermediate shaft bearing assemblies: the change over from double to single occurred in 2001. Early 2001s have the double. Mine was produced in December of 2000 as a 2001 model and it has a double race bearing. The double is hard to get out and the single is much easier. The double makes a rattling noise before it fails, warning the driver; the single gives no warning. Fewer doubles have failed than singles. I installed the Inengineering 160 degree thermostat. Result: on the highway above 60MPH, the temperature gauge needle shows 5 to 10 degrees cooler. When the car slows down in traffic in warm weather, the engine heats up too much for my comfort. Consequently, I am going to install a digital fan controller that uses the existing fan relays and the factory temperature sensor. It will allow me to program when the fans go on and when they switch to high and how much time I want them to run after parking. With this final change, I am confident that I will get much higher mileage than my present 95,000 miles. Cicerosecundus

Perhaps it is time to open another topic or change tht title of this one - because IMHO the 987 and 997 engines are possibly even more likely to be a problem than the 986 and 996 engines.

The new additional problems are - chains breaking (longer and a different route) - tappets wearing through (on variable lift tappets - no 6 cylinder seizing (see below).

I have looked further at the number 6 (and more occasionally number 4 or 5) piston seizures that have been reported Worldwide.

They are always on the thrust side which is also the side that the coolant exits from the block. Now (as already pointed out) the coolant enters the block through small slots and only (in my estimation) about 10% or less passes through the block (the rest going straight into the head) - so the coolant flow speed through the block will be relatively slow and therefore the temperature rise as it passes accross the cylinders will be relatively high. This means it wll also be higher on the thrust side of the 456 side of the block. Older engine designs had ALL the coolant going into the block and then into the head. While this did increase the temperature of the coolant going into the head (whereas it is now cooler as it enters the head) never the less it also lowered the temperature increase (or gradient) inside the block by greater volume of flow and also increased flow rate. This design has therefore made a huge difference to the temperature of the block and of the thrust face of the 456 side of the engine which will be much higher.

The 123 cylinders are the other way around - so the thrust side is the side that the coolant enters the block and is therefore running cooler (because while the entry point is a mirror both sides - one side of the engine thrusts on the top of the cylinders while the other thrusts on the bottom.

On top of that (again as already pointed out) the coolant has further to go to get to the 456 side so is likely to be a slightly slower flow rate and the oil cooler is also on the 456 side so there is additional resistances to flow on that side.

All this adds up to the thrust side of the 456 cylinder running hotter than the thrust side of the 123 cylinders and therefore the oil temperature of the piston to block face on the 456 side will be higher. Perhaps this is why the thrust face of the pistons seizes up whereas the other side is perfectly OK and usually unmarked.

It seems to me that there is insufficient coolant flow and too high a temperature to the thrust face on that side of the block.

I also think the coolant flow is too low in both blocks - but - as always - it will be the weakest point that fails first and this will always be on the 456 side and as the slots have been made with different depths on that side - the flow to each cylinder is slightly different and it seems that the number 6 probably gets the hottest.

We cannot change the coolant flow side to side or top to bottom (which I think would have been better going into the other side of the block on the 456 side) so all we can do is to increase the flow to the cylinders on that side. I also think a lower temperature thermostat would be a good idea (to lower coolant temperatures everywhere) and am presently seeking one - if anyone can help please contact me.

I guess these changes to tradditional temperature distribution inside engines -have something to do with emissions (and admit I do not know enough to explain why Porsche made these differences).

I therefore think we were right to carry out a mod to try increase the flow through the cylinder block on that side of the engine and time will tell if that will prove the amswer.

Baz

Very helpful updates, Baz. Thank you.

Terrible! I can't help but wonder how he drives it, mind. Replaced under warranty? Do they warranty warrantied work? Could be costly.

Good question! I've never had a Porsche warranty so am not savvy as to the ins and outs. Rationally it would make sense that they replace the second engine under warranty. If there's a horrid clause that states a customer contribution for a second replacement I'm certain he'll be none too pleased. Either way, he's looking at Range Rovers now.

It's a 2005 car so presumably is on extended warranty. Not asked but for his sake..

One driver and two engines going the same way. Something to do with the way he drives it perhaps. I get the impression he's a bit lead footed and perhaps not sympathetic towards a cold engine given the way I've seen him pull away from the office. Unacceptable for an engine to let go under these conditions? Perhaps so.