07 S550: Check oil at next fuel stop

[kevm14]

The previous owner told me it does this, before I even took the car home. However, she also told me it's because the oil was overfilled and since it doesn't use any, the message is actually because it's overfull. Fun fact: my E55 told me to add 1 qt while driving it home and I have NEVER seen a message while driving since then, and the oil has been low multiple times. This wasn't on my drive home with the car but it was the next day and the first highway drive I did with it. So this is now a thing.

By some miracle this engine has a regular oil dipstick. But you are supposed to check the oil level on a hot engine (because it may look low on a cold engine AND I also read that the dipstick O-ring can push oil out of the tube and lead to a false low oil level so you can remove it temporarily when checking if unsure). I checked on a warm engine and saw the oil level was between the min/max on the dipstick. Certainly no cause for concern. The oil sensor is a simple float-based system on this car. Nothing fancy. And I'm not sure it is even capable of indicating high oil level. Just low. And it also only checks when driving.

So I need to check on a hot engine on a flat surface. One piece of info is that the previous owner added multiple labels indicating the oil capacity. He wrote 8.5 qts. Well, the capacity is actually 8.5L. That equates to 9 qts which is exactly what my E55 takes, for my convenience. I have no idea if the mechanic filled it with 8.5 or some other number.

I think the plan is to check on a hot engine, flat surface. See what that reads. If it's down from the max, I may try adding like 1/2 quart just to see if the level sensor is just really sensitive.

If the level sensor seems to be malfunctioning, I did find out they are extremely cheap.
https://www.fcpeuro.com/products/merced ... -008891011

However the lower oil pan has to be removed to change it. Before I flipped the table I read up on that and it actually looks like they made it really easy to do. Also requires this RTV:
https://www.fcpeuro.com/products/merced ... 3989982010

Attached various WIS instructions.

Anyway, in conclusion, this could all turn out to be nothing. At a minimum, it SEEMS like the low oil level warning is coming on prematurely (because it seems like it can't be much more than 1/2 qt low based on the dipstick). Or I could just do an oil change, add the proper 9 qts and go from there. So just documenting stuff here since I did all the research already.

Furthermore, if it turns out to be an overly sensitive or, worst case, faulty oil level sensor, I could also just ignore the warning and check the oil once in a while manually. This car has 4k on this oil and if it is still halfway between min and max, this is probably the lowest oil consumption of my entire fleet.

[kevm14]

Cold check not quite on level ground.

It is exactly on max. It may be that their mechanic adds oil until it is at max cold. Which is incorrect and is actually a low level. If that's all true, this also means it hasn't lost a drop in 4k. I'm not going to call that one just yet but I am feeling better about my plan to just change the oil and add the correct amount, then check hot. I could also try checking hot again and see what it reads.

Actually wait. It's at max cold. Shouldn't it be at min? The idea is the oil expands when it warms. But then a cold engine has also had all of the oil to return to the pan. Hmm.

I could also add 1/2 quart (not sure what to add though) and see if that message goes away. It requires a little highway driving to come on so shouldn't be too hard to replicate.

I could run M1 0W-40 Euro. Or the same LiquiMoly MolyGen 5W-40. Given it will be parked outside in the winter I may want to go with a 0W-40. I think that might be spec below a certain temp anyway.

[kevm14]

Checked it hot. Slight incline but not too bad. Looks to be about 3/4 of the way up. So.....not low. Yet the thing came on again today. I guess the sensor is bad. Kinda sucks.

I'd like to be able to trust it because....German car. Not sure if I'll replace the sensor before my Feb trip or not. Does require pulling the lower oil pan. If I was enterprising I'd do it with the oil change it will need in the next 1,000 miles so I have a few weeks to figure this out.

[kevm14]

Bought the sensor and special oil pan sealant from dealer. Right now I'm actually leaning toward replacing it. If it does mostly the same thing (notifies me to check the oil when it's halfway up the crosshatch or more) then I'll just know it's super conservative and it wants like 1/2 qt. I find that silly but if that's how it is supposed to operate, fine.

This also assumes that my reading on the dipstick is accurate but I have nothing else to go by. I am curious what the dipstick reads after a full 9 qt oil change. Does it read overfull? Is the sensor right but the dipstick is wrong? A distraction is the fact that the PO labeled the oil capacity as "8.5 qts" which is 1/2 qt under a full oil change. I don't know if that somehow factors into this. Again the car has like 4k on the oil or so and I'm betting has received zero makeup oil over this period. The claim was overfull but maybe it just got 1/2 quart too little, and then burned another 1/2 qt? That doesn't explain why the dipstick reading looks fine (unless it's wrong like I said).

I COULD just do an oil change and monitor it and save myself from the effort. I am also assuming the lower oil pan is completely accessible because that's how WIS made it seem. If it is NOT accessible well then that's a different story. No plans to lift the engine up or whatever to do this particular job right now.

[kevm14]

I added a little over 1/2 quart of M1 0W-40. The owner's manual actually says the difference between min and max on the dipstick is 2 quarts! It did look like 3/4 of the way up the dipstick but my driveway isn't perfectly flat. Assuming the sensor is working fine, a plausible scenario is that the shop added 8.5 quarts 4k miles ago (it takes 9 qts) and then it burned maybe another 1/2 quart, leaving the dipstick "around" halfway. If the check oil thing comes on when it needs a quart, I am fine with this and not going to replace the sensor. So we'll see how it behaves on the highway. I bought the sensor but certainly don't want to replace it if it's actually working as designed.

Oh, check out what you can see in the oil filler. This startled me at first. Obviously this is how you remove the timing chain.

[kevm14]

It took longer but the check oil thing came on again. However the oil level is still not at max. Maybe it needed a full quart??

So I will add the rest of the quart and then see what the level is and what the warning does.

[kevm14]

Added the rest of the quart (continuing from last post).

Will have to check dipstick hot on a flat surface but that's easier said than done.

[kevm14]

Checked it hot on what I think is a more level surface. It still wasn't on max. Ended up adding another full quart!!

Now seems slightly over max. I will have to check again. Might even want to pull it into the garage to get it as flat as possible. But....this makes me think the sensor is working fine??

Maybe the next time I see the warning it really will need a full quart. Now the only question is....what is the actual oil consumption? Need to do the cam covers, breather cover and centrifuge. Actually I may want to pull the MAF and clean the TB because it may very well be oily in there. Maybe try to rinse out the breather hose, too.

[kevm14]

Checked it in the garage which is the flattest surface on my property.

It's sensitive to level, to how long it sits after you shut it off, and to whether the O-ring is installed on the dipstick. Sigh. Ended up removing the O-ring to get the best reading. The O-ring creates a seal and pushes the column of oil down the dipstick tube giving a low reading. This was probably 30 minutes after shutdown which maybe is too long. But I'm calling this the correct level.

So I guess I can track oil consumption now. Next time I see that add oil thing, I guess I will just dump a quart in? I am thinking the sensor is fine since I have added a total of 2 quarts to reach this level. I guess that means it does use oil.

[kevm14]

So on the return from NH, this warning came on 4 different times. I was getting a little nervous but we ended up just going all the way to my house. Once there, we checked it hot and after I removed the O-ring on the dipstick, the level was just about exactly where I left it before, just above the max mark.

That seems pretty conclusive that I do need to replace the sensor. At least it doesn't seem to be guzzling oil.