driving below 2800 RPM = trouble?

[Bladecutter]

Originally Posted by Brucelee

Unless you are lugging the engine, I would like someone to explain to me how the RPMs contribute to IMS failure? Are you suggesting that a flawed engine design responds BETTER to more internal stress and friction?

How can that be, please enlighten me.

Again, I am not talking about lugging the motor, although I am not sure how the Tip will allow you to lug it if you are in auto mode.

I am open but skeptical!

From everything that I have gathered from the information presented on several other Boxster forums, here's what I understand as being the issue:

At lower RPMs, the Vario-Cam system is actuating the valves at certain rpm ranges.
During the period that the VC system is being actuated, this places an additional load on the IMS, as the IMS is what connects the Camshafts to the Crankshaft.

During high rpms, the cams are already in their maximum position, so they don't place any greater load on the IMS and its bearing. At lower rpms, there is a much greater strain.

Lugging the engine, which technically qualifies as any event that start out at a low rpm in a high transmission gear, with large throttle opening, places a large strain on any engine, but on this engine, because of the design using an IMS, and the weak bearing, this wind up becoming a weak link in the engine.

If you think about most other engine designs, the camshafts are directly actuated by the crankshaft either by a timing chain, a timing belt, or by timing gears. This engine is different, and presents a weak link between the two.

So, here is the most simple way to explain the current thinking on why Boxster engines are having a high rate of IMS bearing failures:

Basically, lugging the engine places a greater load on the IMS and its bearing than is healthy. Excess load on the bearing leads to seal failure. Seal failure leads to oil intrusion, which washes away the lubricating grease in the bearing. Long oil change intervals combined with lugging and cold running lead to fuel contamination of the oil, which leads to fuel contamination of the IMS bearing, which then leads to its failure.

So several things can help lessen the chances of IMS failure:

More frequent oil changes with top quality oils. Somewhere in the 5k to 7500 range is being claimed as the best.

Run the engine up through the rpm range in every gear, and stay away from the 2300 to 3000 rpm range for long periods of time (don't drive cross country at exactly 55 mph).

Have the IMS bearing seals removed to allow constant oil access to lubricate it.

Buy a 2009 Boxster instead.

BC.