Porsche Boxster, Cayman, 996 and 997 engines – the truth

I’ve just been reading a magazine article about the M96 and M97 engines used in Porsche 996s, Boxster, Cayman and Gen1 997s. In essence, it’s a well researched piece but spoiled by  wordiness and the inevitable scaremongering.

So, let’s get one thing clear right from the start. Porsche sold hundreds of thousands of Boxsters, 996s and 997s, and the vast majority have had trouble-free engines. The problem is that the internet and press grab hold of the rare engines that fail and blow the issue out of all proportion. I have done a lot of research on this subject and spoken to many engineers, and I have discovered nothing that would put me off owning one of these cars. I once wrote that I reckoned five percent of M96 and M97 are likely to suffer terminal failure, and was contacted by a Porsche specialist who congratulated me on my feature but suggested that I had over-estimated the problem – he believed it was less than five percent.

So, as they say in America – go figure.

Here’s a brief resume of the M96 and M97 issues:

RMS leak

The rear main seal stops oil from leaking from where the crankshaft exits the engine to meet the flywheel. There’s a fair chance that this seal will leak at some stage in the car’s life, leading to nothing more dramatic than a small puddle on your garage floor. It’s a simple fix and best done when the clutch is changed. Not that other minor leaks can occur from this area which may be misdiagnosed as coming from the RMS. A common problem but not one to keep you awake at night.

Porsche modified the RMS a number of times during its life. The later one is on the left

IMS failure

The intermediate shaft has a bearing at one end which, for some reason, is a sealed unit; odd when it’s located in an oil-filled engine. If the bearing loses its built-in lubrication, the seals mean it doesn’t receive engine oil and it can, occasionally break up, leading to substantial engine damage.

To avoid this rare problem, an uprated bearing can be fitted, or a standard one fitted but with the seals removed. The IMS Guardian monitors for impending failure; click for details.

The IMS bearing – a modified one is on the left

Cylinder bore damage

There have been occasional reports of cylinder walls cracking and breaking up (in a so-called D chunk), but this is very rare. More common is scoring of the bores, most usually number-six cylinder; which seems to affect the 3.8-litre M97 engine in the 997 Carrera S and 4S mostly, and ovalling of the bore. Pistons occasionally break up, too.

Cracked cylinder bores are very rare.

Air/oil separator failure

This environmental device removes any oil from fumes which are then recirculated back into the engine. If this fails, oil will enter the engine, causing the exhaust to appear smokey. Worrying to look at but not usually anything to worry about, and a simple fix.


And that, in a nutshell and without any hyperbole, is it. As I said, there is nothing there that would stop me from owning and enjoying a Porsche with one of these engines. In fact, look on other internet forums and you’d find similar – and just as overblown – stories about other manufacturers’ engines.

The key is to keep your Porsche properly maintained and keep the revs down until the engine has fully warmed up, which is commonsense advice for any car.

This Post Has 9 Comments

  1. Allan

    This is probably one of the most balanced articles I have read on these cars, good job.

  2. Bill

    Very good, balanced view of the M96 engine. The real endpoint on this IMS bearing issue would be to have a specific and reliable number for the failure rate. Please keep trying Philip.

  3. rachael hodgson

    wondered if my boxster has a serious problem… when cold grey/white smoke is emitted from the exhaust and when ticking over it seems to mis-fire. also a small puddle of oil on garage floor.
    in anticipation of a reply.
    Many thanks

    1. Phil

      Hi Rachael

      It’s impossible to know without seeing the car. I suggest you arrange for your local Porsche specialist to assess for you.

  4. Nia

    I agree. Scaremongering sells products and services such as antibacterial soaps. I have seen 996s with over 200k miles on the original IMS still going strong. 1 out 14 people get lung cancer so IMS should be the least of your worries.

  5. Mike

    I have a 2003 996 Carrera 2 with only 47k miles , these comments have me worried should I just get the oil changed to check evidence? It’s all so expensive at Porsche garages, can you suggest a garage or mechanic to check this who’s reasonable in price

    1. Philip Raby

      Hi Mike

      Don’t be worried. Problems are rare but it’s worth having your Porsche regularly serviced. Where are you based?

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