curt_928

Hi everyone,

So I bought my 02' last August with about 20,000 miles on it, used from a dealer in Upstate SC. The car was 4 years old with the Carfax stating one, maybe two owners... and for the most part it's been reliable though I've had to replace an ignition switch (surprise!), a RMS that healed itself and a couple of window regulators...

I have a hypothesis though.. I bought the car as a fun daily driver and I don't autocross it, or get frisky driving it... I hypothesize that by keeping the RPM's below 4000 to 4500 rpm will prevent IMS failure. It currently has about 33k miles.. I'm wondering if the failure is due to rotational friction and oil starvation rather than metal fatigue and subsequent part failure. I think I saw the car being driven around town by a past female owner so not thinking too much abuse there.. although the dealership bought it from did have some kids that might have beaten it...

What do you all think, lower RPM's = less probability of IMS failure?

Curt
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79 928 5sp silver/blk
02 boxster 5sp blk/blk

JW in Texas

Curt,
You should post your hypothesis here:

http://www.boxsterspec.com/index.php?showtopic=1213

& see what Jake from Flat 6 Innovations thinks about it. He knows these motors inside/out & has developed a bunch of fixes for their weak spots.

curt_928

thanks Jay... I think I just might... :-)

Curt
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79 928 5sp silver/blk
02 boxster 5sp blk/blk

arenared

Also visit Flat6Innovations.com (Jake Raby's site). I don't think driving under 4500 RPM is going to make a difference. Besides, there's no point in owning a Boxster or any M96-based car if that's the case since life begins at 4500 RPM. From what I've read, the main culprit is a weak bearing at the flywheel end. IMS failures seem to happen independent of mileage, age, or how they're driven. There are ones that fail on engines with only a few K miles and others that last 100K's of miles. Some fail on daily drivers while others last on cars driven by track junkies.

Ray S

What evidence do you have to support this hypothesis?

Personally, I have never seen any data that would support your conclusion.

blue2000s

Quite the contrary, actually. Everyone who's reported an IMS failure that I've asked was driving slowly in traffic when the failure occurred.

curt_928

Don't have hard data. Have extrapolation from car manufacturers: slower turning v8 with lots of torque versus v6 (original 928 concept) or v6 versus turbo 4 cylinder for longevity. Simply, less wear on the bearings with increasing rotational speeds.
Faster turning engine results in torsional stresses in proportion to speed, revved higher with more changes in engine RPM torse the IMS shaft and stress the bearing. Same reason use dual disk clutch, less mass being turned = less torsion on the component.
In short, no data. Seems intuitive though....

dennisafrompa

...if it makes you feel better, well then you can think that way.
Funny one guy thinks it's coddled cars that fail, another hopes coddling will prevent failure...Truth is nothing will, with any certainty, prevent an IMS failure.

Both mine occured at low RPMs under 35 mph.....so hypothesis away!

Ray S

Between your choices I'd take the M96 Boxster lump over the 928 V8 any day. The m96 has much longer maint intervals and I guess would be far less expensive to maintain over the long haul.

Other owners have made the opposite hypothesis to yours. i.e. that infrequently driven cars or "babied" cars are more likely to see problems.

Personally, I don't buy either side. I think it's a luck of the draw thing in that a small percentage of these motors are defective and are more prone to fail (there are several potential problems areas, the IMS is just one).

Frankly, I redline both of my cars (after a proper warm up) just about every time I take them out and they have both served me well (read virtually trouble free) for many years each.

If you honestly believe that a "babied" usage will somehow protect you if your motor is defective good luck with that. However, I'm sad for the performance fun that I believe you are depriving yourself of.

Again, good luck.

arenared

You're assuming it's wear related. If anything, I think that's one thing that seems to have zero correlation.

smshirk

I think lugging it around would cause the failure, not driving it hard, and I only say that because it's been true of Porsches as long as I can remember. I try to stay in 4th and 5th on interstate in town driving, 3rd on city streets. The sound at 5k is intoxicating. I drive the Boxster a lot harder than my 996, not really sure why, I guess it just sounds better. I have to just keep the 996 in 3rd for a 20 mile stretch everytime I go downtown just to keep it happy. I had 108k on my 97 986 when I sold it, 70k on my 996, and 50k on my 986S with no failures of any kind. I feel better now knowing there are some actual fixes out there, flat 6 innovations, Roock, and probably others have fixes and more HP available once you do have a failure. The 3.2 to 3.6 with 340 hp at flat 6 sounds sweet to me. I almost wish it would fail..............but not quite

insite

i am of the opinion that the cars LOVE to be driven hard. heck, even the owner's manual explicitly says lugging the motor is dangerous. FYI, i drive the bejeezus out of my car and it has 137k on the ODO. i regularly take it to the track and regularly auto-x.

one could also make the case that higher revs produce higher oil pressures & in turn do a better job of feeding the IMS bearing that so often fails.

curt_928

Well everyone thanks for the feedback... it does seem that as of right now my hypothesis may require more information than is available.
I agree with the increased oil change intervals proposed and lugging the engine with fuel starvation.. maybe porsche knows if oxidation of the bearing with use/environmental factors leads to the failure via spalling on the bearing shaft..

Perhaps one day we will know. :-)

Curt
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79 928 5sp silver/blk
02 boxster 5sp blk/blk

Turboflyer

Just a small input as I have no idea why the IMS failures really occur. I do know that "lugging" will only effect main bearings and piston pin bushings. The rest of the engine either sees higher or lower RPMs. Lugging as it is referred to dramatically increases cylinder pressures. This in turn relates to more wear on those bearing points. There is always a happy medium. No engine likes to be lugged. Even Harley riders make that big mistake. Then again there is a point when you are only making noise and no HP or torque with increased RPMS. And to put a spins on all this, engine do not like to be run at high RPMs with out load. Also with ever 100 RPMs there is a logarithmic increase in centrifugal forces. In other words the rotating mas, piston, pins, rods get heavier. This results in , you guessed it, more wear. Wear does increase on all parts with increased RPMS at some point. This is no where near the problem that high cylinder pressures cause. There are a host of other problems caused by high cylinder pressures but that would be another topic. Hope this sheds a little light on the problem. Unlike certified aircraft engines there is no requirement for the engine manufacturer to provide a history of failures and resulting fixes that must be done. And you know Porshche is not going to publish squat. Well unless people started getting killed, maybe.

Achillies

Very interesting M96 article in Excellence this month..talk about IMS issues. THe article indicatres that gentle driving may not guarantee no issues.