Oil level drops from full to minimum after 15 min highway drive

[pb2707]

I'm having a problem with my 2008 e92 m3 whereby the oil level drops from full to minimum after driving on the highway for around 15-20 minutes.

I have already replaced the oil level sensor and recently had a software update and new cam cover gaskets. The car isn't throwing any codes either.

When the car takes the first oil reading, it says its full. After a sustained period on the highway, it suddenly says i need to top it up. If i then start doing town driving again and take a new reading, it says its full again.

Does anyone know what might be causing this? I've seen a similar thread but it didn't have an update from the owner around how to solve it.

Thanks!

[nrubenstein]

Try adding a little bit of oil. Think increments of 100ml. Mine was doing that, and stopped after I added about 200ml. No guarantees, but easy enough to solve if you overshoot a little.

The sensors are garbage.

...although it's not as stupid as the oil gauge in my wife's 993TT. If you fill to full on that gauge, it'll puke oil out the turbos. You have to modify the sensor to pick up oil at a level that won't cause major oil discharge.

[exVtekGuy]

Do you know how much oil was added during last oil change? i have observed the same when the initial oil fill was lower~8.25qt. Last oil change, i put 8.8 qt to begin with and have not seen this issues. Both times i saw the oil at full mark...

[pb2707]

I dont know exactly however i'm assuming they filled it until the oil level read ok.

I dont want to add oil to it because when it takes its first reading it says its full. If i do town driving the oil level stays full. It only drops when i start doing highway driving.

[nrubenstein]

Originally Posted by pb2707

I dont know exactly however i'm assuming they filled it until the oil level read ok.

I dont want to add oil to it because when it takes its first reading it says its full. If i do town driving the oil level stays full. It only drops when i start doing highway driving.

That's the exact symptom that I had. Adding 200mL solved it.

If you overshoot, just drain a little bit out. It's not hard. Pull the plug from the front end of the sump (so there isn't much oil), wait a couple seconds, put it back in.

[Davisca455]

Originally Posted by pb2707

I dont know exactly however i'm assuming they filled it until the oil level read ok.

I dont want to add oil to it because when it takes its first reading it says its full. If i do town driving the oil level stays full. It only drops when i start doing highway driving.

Makes me wonder if the oil level drops you see during highway driving could be related to the sustained RPMs we experience on the highway?
The theory would be that, at the sustained RPMs, the oil doesn't drain back fast enough to read at the upper level, but when we slow down and the RPMs are intermittent the oil has more time to drain, thus showing the higher level during in town driving?

[nrubenstein]

Originally Posted by Davisca455

Makes me wonder if the oil level drops you see during highway driving could be related to the sustained RPMs we experience on the highway?
The theory would be that, at the sustained RPMs, the oil doesn't drain back fast enough to read at the upper level, but when we slow down and the RPMs are intermittent the oil has more time to drain, thus showing the higher level during in town driving?

It's a reasonable assumption. The solution seems to be to add just a little bit more oil.

[Davisca455]

Originally Posted by nrubenstein

That's the exact symptom that I had. Adding 200mL solved it.

If you overshoot, just drain a little bit out. It's not hard. Pull the plug from the front end of the sump (so there isn't much oil), wait a couple seconds, put it back in.

One other oil removal option if you accidentally overfill, is to remove the oil filter cover, then use a turkey baster or transfer pump to pull some oil out.
The advantage is that you don't have to raise the car and you have improved control over how much oil comes out.
The disadvantage is that it might take multiple attempts to get enough oil out depending on how much you over filled.

[Scrippy]

Start your car and let it warm for 2 minutes. Go take a soft chill spin until heat is adequate. Once you have heat and an oil reading park on level ground and force a level check with the turn stalk. On a level surface with motor at temp run a couple resets. I have had a few wonky readings and gotten through by just driving or doing the aforementioned. I do my oil changes so I know when to call bullshit on the sensor and know I'm not over filled or near for that matter. Only my experiences though.

[nrubenstein]

Originally Posted by Scrippy

Start your car and let it warm for 2 minutes. Go take a soft chill spin until heat is adequate. Once you have heat and an oil reading park on level ground and force a level check with the turn stalk. On a level surface with motor at temp run a couple resets. I have had a few wonky readings and gotten through by just driving or doing the aforementioned. I do my oil changes so I know when to call bullshit on the sensor and know I'm not over filled or near for that matter. Only my experiences though.

My experience is that there is a small oil level margin that will cause the oil sensor to go from the top hash mark to "add oil" in about 10-15 minutes of highway driving. In my case, adding a small quantity of oil stopped that. This wasn't an intermittent thing. It was every single time I drove at speed for a sustained period of time.

Yes, it's sensor bullshit, but it still doesn't feel good driving down the highway with the car complaining about the oil level.

[pb2707]

Originally Posted by Davisca455

Makes me wonder if the oil level drops you see during highway driving could be related to the sustained RPMs we experience on the highway?
The theory would be that, at the sustained RPMs, the oil doesn't drain back fast enough to read at the upper level, but when we slow down and the RPMs are intermittent the oil has more time to drain, thus showing the higher level during in town driving?

This was my assumption too but after phoning some specialists, they thought it'd be smoking a lot if there was a blocked oil return and it doesn't smoke or burn oil at all

[pb2707]

Originally Posted by nrubenstein

My experience is that there is a small oil level margin that will cause the oil sensor to go from the top hash mark to "add oil" in about 10-15 minutes of highway driving. In my case, adding a small quantity of oil stopped that. This wasn't an intermittent thing. It was every single time I drove at speed for a sustained period of time.

Yes, it's sensor bullshit, but it still doesn't feel good driving down the highway with the car complaining about the oil level.

I'm going to try this and i'll take some out of the filter housing if its overfull. The trouble is i have no idea if its something more serious or if its just the sensor being temporamental

[Davisca455]

Originally Posted by pb2707

This was my assumption too but after phoning some specialists, they thought it'd be smoking a lot if there was a blocked oil return and it doesn't smoke or burn oil at all

Sorry, the theory wasn't meant to imply that there is any blockage.
It's that when the oil pump is at a prolonged increased flow rate (highway driving), it's pulling oil from the pan at a slightly faster rate than the oil can physically drain back to the pan giving you a slightly lower oil level reading at highway speeds.
Then, when you are driving in town the oil pump isn't drawing from the pan at the same higher rate as when you were on the highway, so the level reading would normalize at a higher level.
This is all a theory.

[brettcp]

I had inconsistent oil level readings like crazy until I updated the i-step level of the car (was still on its factory 2012 software version), issue went away completely and has been perfect since.

[akkando]

Originally Posted by Davisca455

Sorry, the theory wasn't meant to imply that there is any blockage.
It's that when the oil pump is at a prolonged increased flow rate (highway driving), it's pulling oil from the pan at a slightly faster rate than the oil can physically drain back to the pan giving you a slightly lower oil level reading at highway speeds.
Then, when you are driving in town the oil pump isn't drawing from the pan at the same higher rate as when you were on the highway, so the level reading would normalize at a higher level.
This is all a theory.

Why isn't this a problem on the majority of cars? My car over time shows that oil level drops slightly. It goes from full, to down a 1/4, down 1/2, down 3/4, to add a 1 quart. It loses oil faster than I'd like, but we're talking over hundreds or thousands of miles here, not 15 minutes. It's never said it's down oil, then later claimed it's not, it's always been consistent.

[nrubenstein]

Originally Posted by brettcp

I had inconsistent oil level readings like crazy until I updated the i-step level of the car (was still on its factory 2012 software version), issue went away completely and has been perfect since.

My car was updated to the latest software late last year. No change in behavior before or after. That was one of a number of reasons why I had the update done, but it didn't solve that.

[Davisca455]

Originally Posted by akkando

Why isn't this a problem on the majority of cars? My car over time shows that oil level drops slightly. It goes from full, to down a 1/4, down 1/2, down 3/4, to add a 1 quart. It loses oil faster than I'd like, but we're talking over hundreds or thousands of miles here, not 15 minutes. It's never said it's down oil, then later claimed it's not, it's always been consistent.

I don't think there is an actual problem, I just thought that the OP was asking what could explain why the the oil level reads lower at highway speeds than it does in city driving or idling?
If the oil doesn't drain back to the pan, at the exact rate that the pump sucks it from the pan, then I would expect to see a difference in the level reading between sustained highway driving and idling.
I really don't believe the volume of oil in the system is actually changing, only that the level that the sensor reads is varying, based on how hard the pump is pumping.
But that's only an assumption I'm making because I'm skeptical that the oil gets back to the pan as fast as the pump can remove it...at sustained highway speeds.
A dipstick only gets used when the engine is off, so the data points should always be the same, unless there is an oil leak or some sort of oil consumption.
But us super lucky M3 owners now have a "real time" level sensor, instead of a dipstick. Hooray!

[pb2707]

Originally Posted by nrubenstein

My car was updated to the latest software late last year. No change in behavior before or after. That was one of a number of reasons why I had the update done, but it didn't solve that.

My car had a software update last week to try and solve this issue and it hasn't. Drove the car home which was about 120 miles (190km) and the warning didn't come on. Drove it for 15 minutes the day after and the warning came on.

My worry is that the bottom end is getting starved of oil when the cars running at sustained RPM for a longer period of time. I'm going to try topping it up with a tiny bit of oil to see if it makes a difference.

I managed to find a similar post about the issue here (https://www.m3post.com/forums/showthread.php?t=1381986) but there didn't seem to be a resolution.

[nrubenstein]

Originally Posted by pb2707

My car had a software update last week to try and solve this issue and it hasn't. Drove the car home which was about 120 miles (190km) and the warning didn't come on. Drove it for 15 minutes the day after and the warning came on.

My worry is that the bottom end is getting starved of oil when the cars running at sustained RPM for a longer period of time. I'm going to try topping it up with a tiny bit of oil to see if it makes a difference.

I managed to find a similar post about the issue here (https://www.m3post.com/forums/showthread.php?t=1381986) but there didn't seem to be a resolution.

These cars take a huge amount of oil. I wouldn't worry about the oiling difference that a fraction of a quart makes.

[GotV8?]

Theres a gremlin inside your motor!!! jkjk.....All jokes aside, every oil change my sensor does take 1-2 days of driving until it goes to full reading.... IMO, As long as you know you put 8 Liters of oil and do Not see any leaks or excessive seepage, then you are good to go. Our Oil level sensor has a mine of its own and sometimes doesn't want to show up For WORK!! lol

[pb2707]

I'm going to add 200ml of oil to see if that fixes the problem. If it doesn't, i'm going to take it to a specialist to see if they can resolve it.

Earlier on today, the low oil warning came on just after i'd taken it on a 'spirited' drive (not on a highway). I'm wondering if when it comes up to temperature and it thins, the sensor doesn't think there's enough in there...

[nrubenstein]

Originally Posted by pb2707

I'm going to add 200ml of oil to see if that fixes the problem. If it doesn't, i'm going to take it to a specialist to see if they can resolve it.

Earlier on today, the low oil warning came on just after i'd taken it on a 'spirited' drive (not on a highway). I'm wondering if when it comes up to temperature and it thins, the sensor doesn't think there's enough in there...

Warm oil expands, so it's not that. My assumption is that some oil stays in the head during sustained RPMs. There might also be a little bit of oil that goes into the oil cooler when that opens up as well.

Edit: Also, the 200mL that I added may not be the right amount for you. You'll likely need to experiment, and I would do that a bit more before taking it to a shop. The shop doesn't have any magical diagnostics for you to work with here.