IMS failures on automatics?

[Homeoboxter]

Originally Posted by Racer Boy

The oil isn't just in the heads when the engine is running. Think of the oil pump, the cooler, and all the oil passages throughout the engine. All of those add up to a fair amount of oil being in the engine, and not the sump.

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.

[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.

[Homeoboxter]

Originally Posted by JFP in PA

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.

I don`t understand how it makes sense to say anything about oil level in a running engine using either a dipstick or a level sensor. The IMS, the sprocket and the chain are all spinning in the oil, splashing oil everywhere in the case. Itt`s like determining precisely the water level in a running washing machine with a stick. Good luck with that.

Thanks, I really appreciate that you gave a slight chance to the possibilty that my hypothesis might have some relation to reality

In normal conditions the oil mass is not sloshing too much, in race cars it may be, so baffling makes sense there. And so does deepening the sump, providing more oil that can be chilled more effectively. These are useful features in racing, but that doesn`t necessarily mean that these features have anything to do with the oil level or the IMS bearing`s lubrication.

I was talking about normal operational conditions though. And I still don`t get where would about 1-2 quarts of oil go when you just simply turn on the engine.

I also have difficulties in understanding how can it be claimed for sure that the IMS is lubricated by oil mist. To safely say that, you would need to insert a glass window into an engine case to see the oil level, or directly onto the IMS flange, so you can see the bearing during operation. Or you could fit a small boroscope there, but how would you do that? Once you turn off the engine, the putative window or camera would be overwhelmed by oil. It`s not a trivial experiment to do. That`s why it would be great to know where this whole oil mist theory coming from.

The GM engines cannot be compared to flat engines in this regard, because as you pointed out, in a flat engine much of the oil coming out from the heads (which is still nowhere near to 1-2 quarts because of the small orifices that won`t let the oil warm up too much in the relatively hot heads) will not return to the sump because the scavanging pumps are not running.