Oil pressure drop, oil aeration?

Last weekend I was on a nice drive thru the alps and at one time I noticed that the oil pressure went down a few times to around 2-3 bars (fluctuating) and then returned to normal (around 5). This happened on a slight incline, at around 4k rpm, no hard turning, steady speed. Before arriving at that road I had been on the high way for around 1h30m and 30min of small roads thru villages(thus, engine properly hot). Ambient temp around 27c. Coolant temp had been in the 105c area for some time due to rather low speed driving and A/C off(= fans off). I think what I saw was oil aeration. I'm thinking that the oil had reach such a temperature that it gets thin, circulates faster thru the engine and thus the air never really escapes the oil. Could this be right?

It might be a oil pressure switch on its way out, or at least dirty lead wires to the switch. A hot engine shouldn't read 5 bar of oil pressure. My car had the opposite problem - oil pressure went to zero after changing the oil. A new oil pressure switch solved that problem.

Last month I change the oil pressure sensor, it is tested and properly working. The pressure drop I saw is most likely a real pressure drop. Edit: My old sensor showed too high idle pressure and at the same time never above 4.5bar.

What type/weight oil are you running?

Spirited drives can cause pressure drops in the curves. Get a deep sump pan and make sure the level is in the middle of the dip stick. This is the solution for track cars assuming there is not an additional issue. Dont trust the dash gauge.

The drop occurred in a slight bend and on a straight, both with slight incline, far from any extreme driving. The pressure sensor I've check properly, it works without glitches. Not before or the 300km after there was any drops that I could see(but engine was generally colder) . Oil is x-cess 5w-40 with around 2000km on it. When I got back home I checked the oil level according to the manual (hot and a few minutes after stoping the engine) and it showed 3/4 to full(dipstick and digital showing the same).

First thing I would do is an oil/filter change even though you only have 2000km. The new Porsche classic oil for our engines is a 5w/50. Might think about trying that.

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Yes, an oil change is coming up now in the fall. I have around 1000km more to do this year for collection of some Champagne and whiskey, I think it will survive just fine since it's mainly flat terrain and higher speeds. Before deciding on a different oil I would like to get some more information if this might be helping or not for what I saw. But I think your right that I should get something thicker.

These cars, with some types of oil, certainly have aeration issues. But most of those reported have been on the track, and mostly in the turns. Right-handers and more common, but left-handed turns can as well. Some have reported on twisty roads with spirited mountain driving. Given your issue, I would suspect oil pickup in the sump - if you haven�t checked yet for the depth of the oil pickup, to make sure it�s at the proper depth - and to check the bypass valve/spring combo on the pump and there�s one on the filter as well. Perhaps the bypass/spring has an intermittent problem. The other thing it could be is a faulty scavenging pump that�s not operating correctly. While aeration can be a problem, unless you were really flogging it, I don�t know if that�s the first place I would go. If you really think that�s it, just swap it for race oil (or an oil that�s known to not have aeration) and run the same test. One last thing: was your 105C water temp taken from ODBII or the dash gauge? If ODBII, that�s a pretty warm engine, which would suggest oil temp could be approaching 250F, which would result in a lower pressure overall. But since you are at 5 bar when the oil pressure issue does not exist, it doesn�t seem like a temperature problem. Even if oil was approaching 250F, your pressure would stay between 2-3 bar at speed, not spike up and down like that. I don�t doubt you are losing pressure at times here.

At the time I had 150kg of passenger/luggage in the car and was driving moderately spirited and it was going up hill. I see several reasons why the engine temp could be very high. If there was an issue with the pick up and/or the pump, wouldn't it show up also with a cold(or normal temp) engine? Is it the oil pickup O-ring that maybe needs replacing? I will drop the sump at the next oil change to have a look. The temp was from OBD. After changing the chain tensioners this summer the oil pressure definitely raises quicker with revs(checked with fresh pressure sensor). I now normally see 5 bars around 4k RPM with a hot engine. The oil pressure in this instance drop down to 2-3(from around 5) and then came back. It was not swinging up and down from the normal.

I live in the Sacramento CA area, going for spirited drive in the hills in high 90s F I would see 220 F OBD reading all the time, big difference to me was changing from a 5W40 oil to a 5W50 and seeing better press. and even at idle. I don't think you have blockage in the oil pick up but might drop it to check your baffle doors or even upgrade.

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I don�t think it�s likely to see oil starvation with a cold engine unless you are several quarts low on oil. I don�t think the volume is high enough to drain the sump when cold.

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I agree that moving from 40 to 50 will result in higher pressure on this engine, but for my car, it was only about 1/2 bar. And since I�m well above 4 (and the OP is at 4+ bar) already, pressure is not needed here. Rather, the sucking of air (cavitation) or the pumping of air/oil mix (aeration) seems to be the issue that needs to be resolved.

I don’t know if I trust the stock oil pressure sensor to be accurate enough for this fine of work. I’d try a more accurate measuring device before getting too carried away with diagnostics.

I had the same issue on the track, after about 5 or 6 laps, when I went around a long sweeper, the oil pressure would drop to 2-3 bar and then come back up on the straight. It's the oil pump being starved or slightly starved, usually happens when the oil is hot. Considering I've been driving in the mountains the last six weeks, going around twisties and using the engine as my brake (high RPM's), I see high coolant temperatures during these times. I imagine it's the same thing with you. Not much you can do about it, I wouldn't be too concerned.

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Hey Paul! Did you lose oil pressure in the mountains or just the track? I�ve heard some folks add a switch that turns on the high speed fans at will. I always thought I could do this, but then again, the DME should know when temps are too high and do the job itself.

I just lost the pressure on the track, I have not been pulling the same g's in the mountains, I'm an old man, but the engine definitely gets hot when you are at 3-5K the whole time. Lots of friction going on that doesn't normally happen. Still in West Virginia after six weeks, hopefully only one more to go. I miss home.

The thing is, my pressure dropped down on a straight and in a low G turn. Thus, I don't think it has anything to to with the pick-up sucking air(unless it's leaking at the O-ring) but rather aeration. A mention of the oil pressure sensor. I've taken one apart to check inside. Inside is a metal membrane which moves a wiper across a resistive plate. The sensor is sensitive but probably not that accurate in absolute terms. Good for measuring relative measurement but maybe a little inaccurate in absolute measurement.

The issue with oil pressure drops in turns is caused by excess oil flow and aeration from the excess flow, due to loose clearances within the engine. Loose clearance is usually good thing in a high RPM engine so the more oil flow will keep bearings cooler, but with the M96, high oil flow and increased aeration/slow return equals pressure lose in turns. Using more oil capacity (2 qt deep sump) and thicker oil with low aeration (50wt or 60wt) are the only cures. If you still have problems after this, time to tighten up the motor.

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Thank you very much. Apart from the oil weight, is there anything else which can help in regard to aeration? I'm thinking if there are special oil formulations with more/less of some additive.

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Not much else to do, if a 2 qt deep pump don't fix it, check both scavenge pumps , then use a thicker oil 50wt or 60wt..If that doesn't fix it, it is beyond simple fixes and a rebuild in in order. New/fresh tight engines don't have this problem. None of the oil companies give out data or tests on the aeration of their oil. Silicon is the main anti-foaming additive in the additive package.It is safe to assume that racing oil will have less aeration/foaming.

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After some googling for a good oil something came to mind. I change the sump from the standard to a X51 this spring. While sealing it up I used Loctite 574 and then just filled up oil and didn't think more about it. Could it be the leftovers of 574 in the engine oil which makes it more prone to aeration? Oil wise I figured out that my best bet is to move to an ester based oil. There seams to be a consensus that heavier weight will cause higher temperatures, better to move to ester based oil since I can keep using 40wt but with the added benefits of what normally a heavier oil would give. Since I don't have an oil pressure issue when everything works correctly, this seams like the way to go. And the way I drive my car, weekend car for fast driving, the esters protect better during the cold starts also.

The research continues. I've been reading other forums (non-porsche) and articles about aeration issues and I've found something interesting. I've read that a common generator of aeration is the oil pump by pass. When running too much pressure the oil starts recirculation via the by pass and aerates the oil. This was rather spot on since I have mighty strong oil pressure after changing the chain tensioners recently. And the pressure drops is at high RPMs. So, I'm scratching my head if I should maybe run a thinner oil instead. My big question about this: As long as oil pressure is high enough, there is no problem? The original manual states that 5w30 can be used so 30 weight should be ok to maybe test?

Let me say that I learn so much from these forms and wish to thank all the knowlegeable contributors for expanding my understanding of these engines. I live in the California Desert where we see temperatures of 115 F + and often higher. I run Joe Gibbs DT40 which was a reccomendation from my mechanic at the time of IMS replacement. At these temperatures, when my 2002 C2 is at a stop light and idling it, loses all oil pressure and forces me to boot the RPM to 2500 to turn off the red dash light warning. Is this caused by aereation? I just assume the oil has become too thin at these temperatures but perhaps there is a bigger problem.