dzung said:
I too had the same model before changing over to a 996, 3.6 Carrera 4. Absolutely love it to bits and on track I am a bit faster than my M3. Very similar though performance wise. I too debated the 4 versus 2 and not much in it. If you use it everyday in snow and ice then maybe 4. However subsequent generations are progressively dialing out rear ended feeling and lift off oversteer. I think my 4 more stable at high speed but lose some of that nice front end lightness of the 2. Lots of scare stories on the net. A very good article in Total 911 magazine this month summarising the IMS with comments from Hartech and Autofarm on the topic. Basically For the 911 changed to a sealed bearing for the IMS. So with wear in a small% you get faster wear of bearing without lubrication from engine oiling. This leads to imbalance, more heat, friction perpetuating cycle till failure and secondary total engine disaster. People reckon 5-10% of engines may have this problem. Porsche redesigned bearing, shaft, securing lug several times in life of 996 but never fully fixed it until the mark 2 version of 997. Theory is that higher mileage cars less likely to have IMS failure as sone wear allows oil in to lubricate and cool. Best prevention according to experts is warm up engine properly before >3000 revs, use 5/40 oil rather than 0/40, once warm don't be afraid to use whole of rev band rather than lugging around all the time at low revs. Regarding the cylinder liner problem, cracking this also tends to be overestimated, again 5-10% maybe. Thinking is that with water cooling and thinner walls, uneven heat , and due to minor flex in block. Once again same advice re IMS and make sure oil levels allows ok. Don't be put off by scare stories they are cracking cars
The biggest problem with low mileage cars is the familarity and/or mechanical care taken of them. If you jump from one toy to another and can't remember or don't care what it should sound like or feel like and you hammer it from cold 'cos its just a toy, not a passion. Then your car will die. Any car, not just a Porsche.
Find an example that has been owned by an enthusiast with mechanical sympathy and understanding, that has been loved, treated with respect, looked after, cared for and no expense spared and you won't go wrong.
The C4 is idiot proof, has (slightly) better weight distribution, heavier feel and more stable steering, stronger front chassis/bodyshell (which is why the GT3/GT2s use the C4 or Turbo shell) and less than a tank of fuel heavier. Most of the time the split is 95% RWD and 5% FWD. Rising to a maximum of 60/40 RWD/FWD.
Read Autocar's review of the C4 here (halfway down):
http://911uk.com/viewtopic.php?t=57277
Not convinced about the balance of that Total911 article, given its remit. Afterall, a paper on how cancer kills you is not balanced unles it covers how often you don't get it. Particularly if the quotes are from the two biggest annti-cancer drug companies.
I have great admiration for both Autofarm and Hartech and have spoken at length to both Robin and Barry, but that article was possible edited for space, if not effect.
I am not sure who these "people" are who reckon the failure rate is between 1 in 20 and 1 in 10 996s and Boxsters exploding! Half of London would have been at a standstill!
All Porsches, and especially 986/996 are subject to continual improvement. From 986/996 onwards development was subject to a formal Kaizan process. Most revisions occur at MY change over, however, priority engineering revisions can occur immediately the change has been authorised and the line or supplied part spec modified.
Because of this IMS design has changed many times during 996.1, 996.2 and 997.1 life-cycles. Of course the 997.2 avoids these issues by not having one.
The IMS engine failures for the 997.1 are estimated at lower than 0.005% at five years.
Many commentators moan that Porsche just doesn't care about the IMS, but their continual development and final total re-engineering (even given the last IMS iteration's relatively low failure rate) is testament to the fact they were not going to ignore it or be beat by it.
The suggestion that "Theory is that higher mileage cars less likely to have IMS failure" is strongly anthropic.
That's like saying the oldest people have not died yet. Everyone who survives to not yet be dead has also lived every other previous age. Those that die young will only have reached a lesser age. Until every 996 dies we don't know the overall failure distribution is.
It's almost counter-intuitive. If there is a running 19k miles 996 for sale now, it still works. Who's to say it won't reach 200k miles with careful use.
The distribution of a finite set looks odd whilst you are in the middle of it.
If human's had only existed for 30 years would we suggest (wrongly) that most people die young as the only people who have died have never been older than those still living.
As any engine increases in mileage it will wear, give the low mileage more use and they will wear the same. Howvever, all things being equal, the IMS will need lubricating in proportion.
The next point re: Mobil 0w40/5w40 is effectively contradicted the previous IMS lubrication theory. If you want oil lubrication by "leakage", 0w40 is your man. So thin at cold, even Porsche can't stop it escaping when they want it to stay in place!
There were specific casting failures with batches of early 986. Although rumoured, these never impacted the 996. The failure rate is again a long way from the suggested 1 in 10 or 1 in 20 (which between just these two issues would imply as many as 1 in 5 911s would die of engine failure!).
The issue with the M96 design is with cyclinder 6, specifically, is under-lubrication and over heating due to under-lubrication.
Get an X51. With additional cooling (centre rad) and lubrication upgrades (high-G sump baffles, second oil pump and additional oil line to bank 4,5,6). Those two otions are almost worth the entry ticket alone: going someway to mitigating the seizures.
Water cooling was specifically chosen by Porsche to allow even and uniform cooling. Pumped water if far more controllable and stable than air cooling. There is no way Porsche could extract either the power or under regulatory threat, the emissions and economy (due to air cooled inefficient burn) they have did with the M96 engine onwards.
In total contradiction, thin walls (with low specific heat capcity and little insulating propeties) and water cooling allow for the removal and control of hotspots.
If air-cooling was so great, how come only Porsche and Trabant (outside of other industries with specific small scale engines or aero applications) were the last companies to use air-cooling?
The best advice ref: cylinder 6 is mechanical sympathy. Fully warm the engine by driving at less than 3,000 rpm or lower (I drive at less than 2,000 rpm until warm - that's still 50+mph in sixth) until the oil pressure at idle drops to at most 2 bar. Then have fun.
Never let the oil level drop outside of range (ideally keep topped up little and often if required). Porsche advise post run-in, normal "early-life" usage at 1L per 10k miles. AFAIK mine uses nothing between services.
On the aircooled/water cooled subject, it not quite as clear cut as the 993/996 interface.
The very first Porsche water cooling was back in 1978 with the 935/78 or "Moby Dick"
The water cooling was done for many of the reasons as the 996 (re)volution, packaging compactness and more importantly, performance.
In order to either facilitate or safely maintain high power per litre it is first necessary to develop a an environment where temeprature may be consistently controlled (for best burn) and it is necessary to carry away excess heat much more efficiently or else you will heat fatigue diffrentially across the engine.
Additonally, water cooling is pretty much the only efficient way to cool multivalve heads efficiently. The only reason the 996 could go multivalve (for emmisions and power) was water cooling.
Next up on the water cooling front was the 1979 "Interscope" Porsche IndyCar racer: (note the rear-mounted water radiators, in front of the rear wheels)
Next up was the 1980s, with the TAG-Porsche partnership Formula 1 cars:
The 1986-1989 959 was a watercooled hybrid (see 996/997.1 GT3 and Turbo below)
More recently there was the GT1:
It was only a year ago (2009) Porsche finally stopped (partially) air-cooling.
The
ALL 996 GT3 and Turbo and 997.1 GT3 and Turbo were all "hybrids", being both air and water cooled (the multivalve heads are water cooled as are the cylinder sleaves, the block/crankcase is air cooled).
THESE AREN'T AIRCOOLED (finally):