IMS failures on automatics?

[JFP in PA]

Originally Posted by Homeoboxter

True. But it`s a closed system. The oil that circulates will not flow back to the sump when the engine is off, or at least most of it remains in the oil lines, cooler, pump, etc. If this wasn`t the case, the main bearings would be starving of oil at every start up and they would fail shortly. When you pull apart an engine, especially a boxster, oil is flowing out from every oil channel and gallery producing a huge mess on your garage floor, even though you already drained the sump. When the oil pump gears are not rotating they seal off and won`t let the oil flow back to the sump. As a result, oil level should not change much during engine run vs stop, IMHO.

Which fails to explain why 5 min. or more is needed before the digital oil level gauge reads correctly on a hot M96.

The dipstick will show spots of oil when the engine is running, not a wet level.

If your hypothesis was the case, why do most people that race these engines both improve the baffling in the sump and deepen the sump, or move to a true dry sump it the rules allow? Because the low level of oil remaining in the sump can easily slosh to the side and uncover the oil pickup leading to pressure loss, oil starvation and some rather unfortunate damage. The oil level remaining in the sump on a running M96 is MUCH LOWER than you think.

The number one lubrication modification when seriously racing any engine is to CONTROL oil movement within the engine. Normally this. Is accomplished by literally jetting certain oil passages to limit the amount of oil going to places that don’t need much oil volume and cleaning up the passages to help get the oil to critical components like the rod and main bearings.

Some GM engines that normally carry 7 quarts of oil in the sump can get as low as 1 1/2 to 2 quarts when the engines pass 4-5K RPM because most of the oil is up in the heads; putting jets into certain oil passages cuts the oil trapped up top to 1-2 quarts, and this is in a nearly vertical v8 design engine case where gravity is your friend when it comes to getting the oil back to to the sump. Porsche’s cases are horizontal, and drain back by just gravity is not sufficient to get the oil back down to the sump, hence the scavenger pumps, and still most of the oil is still not in the sump, but up in the engine.