Questions on digital oil level sending unit
 

2 weeks ago I was at Watkins Glen for a HPDE and I had the blue smoke cloud from AOS flooding on the sharp left downhill turn 6. My check engine light came on, and stayed on the whole 250 mile trip home. but now it is out. I think my digital oil gauge may be faulty. I have the Mantis Sport oil sump extension kit 1, which adds 1.2 liters of sump capacity, and I started the event with the digital oil level one bar below full. But when the digital oil level gauge shows one bar below maximum, or maximum, the physical dipstick shows the level is above the top notch on the physical dipstick. The AOS only has about 15,000 miles on it and my car is going into the shop to be looked at and have the oil changed in a couple of weeks. So I'm starting to think the sending unit on the digital oil level gauge is a bit wonky, and I had an issue at the track because the engine was over filled. I have been using Red Line full synthetic 15W-50.

I tried searching and saw some posts where people thought the type of oil they used affected the digital oil level. I also found that the digital oil level sending unit is a long cylindrical device that is installed from the top of the engine, underneath the intake manifold, and it looks like the intake manifold needs to be removed to change the oil level sending unit.

My questions are, does the type of oil used really affect the operation of the oil level sending unit? Is there any way to test the operation of the oil sending unit, including inspection by dropping the oil pan? My shop has already advised me I can run a lower oil level with my deeper sump, and that's what I plan to do going forward. If there is no easy fix for the oil level sending unit, I may end up just relying on the dipstick and ignoring the digital level.

https://cdn4.pelicanparts.com/techarticles/Porsche-996-997-Carrera/26-FUEL-Replacing_Engine_Sensors/images_small/pic03.jpg
Here's a pic of the sender. I think you need to remove the intake crossover to get to it (it's right next to the knock sensors). It's a long tube that runs through the engine itself down to the sump pan where a loop is submerged in the oil and the level changes resistance on the loop, which changes the voltage read by the sensor. I'm not sure how a different viscosity oil would affect that reading. I run 20w50 in mine and now that I think about it the sensor did read a bit wonky at first but after a few runs the levels match up well between the digital guage and the dipstick.

Running a high oil level isn't what caused your blue smoke though. I realize that accusimps and deep pans are popular, but the Achilles heel of our moist sump (of whatever the hell porsche called it) is in the scavenger pumps - more specifically, their location. Random tangent (which will come back to a point) in 3....2....1....

Bank 1s pump is located in the flywheel end of the bank, bank 2s pump is located on the pulley side. The problem comes with high g cornering and bank 2 - all the oil winds up in the flywheel end of the bank and can't get back to the scavenger pump.

Why did this matter? The main pump moves 20L+ per minute at high rpms, which means 10L/bank/min. Which means that if you hold a high g turn and starve that pump for 60 seconds, your entire oil volume is sitting in that head cover (and yes it will hold that much). This is why accusumps and be deep kits don't work on the track - were talking the ENTIRE oil volume, not 2L.

You got lucky. By overloading the valve cover, you sucked oil into the aos and you smoke bombed the track. You probably slowed down at that point, which saved your engine. If this hadn't happened, you would have needed a ride home.

If you don't believe me about this, look at the oiling modifications for the x51 series 996. There were a few, but the most important one was replacing the bank 2 scavenger pump with a dual stage pump that had a second feed line that came from - you guessed it - the flywheel end of the bank. My point is don't drop your oil level. If you're worried about smoke bombs, put in an oil catch can between the AOS and your intake. But, then you won't have your warning signal either.

If someone wanted to do something REALLY NEAT there would come up with a sensor that alerted the driver to that pump sucking air! Or figure out how to retrofit a 2 stage pump to bank 2. That would be sweet.

Diatribe over. Thanks for those 2 minutes of your life ;)

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Thanks, I hear what you're saying. Why do you suppose other M96 and M97 powered Boxsters and Caymans driving on this track much faster and pulling higher G's than me weren't also smoke bombing? I doubt they all had any modifications to address this issue.

Now that I can't tell ya. It's gonna have a lot to do with individual circumstances from a driving (rpm, duration of forces, attack angle on the curve, etc) and possibly mechanical (oil viscosity, engine temp) standpoint. It may sound silly but the most protective thing to do may be keep the rpms low (minimizing the main pump flow) in the hardest part of the longest turns, but that is just theoretical speculation.

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