Hello, everyone.

I recently aquired a used mercedes C300e (estate) (year 2020) with 34.000km on the clock. Today i decided to check the oil level and discovered that it was too high. From the attached image you can see that the level is almost 10mm above the maximum mark. I found this odd, because the oil level was presumably checked by an independant workshop before the car was sold, and they said it was within norm. When measuring the oil I have followed the exact procedure described in the manuel. I ran the car to operating tempereature (90 celcius), turned off the engine, waited for 5-6 min, pulled out the dipstick and wiped it, put it iback in again, and waited for 3 sec, pulled it back out and read the oil level. Did several readings, with the same result every time. The car stood in a parking garage with a level floor.

From what i understand, 10mm above max mark would indicate almost 0,5 litres of excessive oil. How critical is this for the engine? I think it has driven almost 1000-1500km since the oil was changed. Maybe even more...The car is running fine, without any wierd noises, smoke, or oil leaks. And does anyone here know if this spesific model will notify the driver if the engine has too much oil (on the intrument cluster)? The user manual states that there is indeed such a warning, but it notes that its only for certain engine models, and there is no mention of which engines this relates to spesifically. I believe my car has the M274 engine, and since it has a dipstick, i would assume this car doesn´t show the "high oil level" warning.

I love the car, but im really worried that the engine and/or catalytic converter may already have suffered damage due to this overfill

oil way above max mark

 

I always overfill. Last time I checked the oil was on the cable, but the level varies a LOT depending on when you check it. For example, if I check it after sitting a day it can read nothing, but if I put the dipstick back in and check again it's full. Or if I check after an hour it may read in the middle. I should say this happens on my M276 and M278 engines. I've never seen it happen to any other car or eng, ever. So it may just be those engines, maybe other MB engines too, I just don't know.
It doesn't always do that no oil thing btw, it's maybe less than half the time, but it does do it. I had a witness verify, and others on the form can attest.
So imo the only thing you can really do is drain it, then fill with the official amount. When it varies after that you can only speculate if it's low or just reading funky.

Imo the only time high oil level would be an issue is if the crank is touching it while running. There's also a theory about a roping effect than can occur, and supposedly it's been proven, but a hard pill to swallow. It claims the oil will somehow, magically, defy the centrifugal forces and cling to the crank. So your crank ends up a big sci-fi looking slug of undulating oil which leaves your pan dry because all the oil is on the crank.
If the oil were to magically do this, then the oil level is no longer high enough in the pan for it to do it? Perhaps it only needs some oil to start the process, then it collects more and more oil as it goes. Except the crank is already oil fed and covered so this would happen anyway, yet it does not. Like I mentioned, a hard pill to swallow.

I do have a mystery oil issue in my truck where it seems to be doing exactly that. If I over fill it will cause the pump to suck air above ~3500rpm or so. No clue why it does this. I then added a crank scraper to prevent/minimize this mystery roping effect. It had no effect.
If I'm too low on oil it sucks air the exact same way, so I can only assume the overfill is somehow causing the oil to not be in the pan, but wth, where is it? It could be suggested that the oil was foaming up, but at higher rpm, where this issue happens, the oil is well clear of the crank.
Gremlins is my only theory for the truck and my dipstick issue in the cars.

I consider your oil level perfectly normal, but if you were really worried about it you could add an oil pressure gauge to see if psi moves around a lot. Normally psi is steady and rpm dependent. So above say 2500rpm it should be, lets say, 50psi. If it's moving all other place from say 20 to 50, you're sucking air. Will it hurt it? Probably not, but if you were to see that I'd adjust the level up/down to make it stop. This is exactly how I did it with my truck, but it is also the only engine I've ever had this issue with.

 

An overfilled oil reservoir can ruin an engine, easily. I have some theories as to why.
Suffice it to say, oil, like many other liquids, is incompressible.
If oil is contained, and an attempt is made to compress it, you get the same results as frozen pipes.
Not pretty.
Not cheap.

 

If you can get your hands on an oil extractor you should extract the extra oil. If the oil is high and over the max that can cause a problem with the oil as it begins to get whipped by the crank and turn into oil with lots of air in it. As the process get's worse the oil will start to breakdown and provide no more protection to the engine.

 

When the foam gets sucked up your oil pressure drops despite the overfilling.

 

Reason why the first check is empty is stated in this thread. The operator's manual also have the correct way of checking it.
https://mbworld.org/forums/e-class-w...ml#post8940638

 

on my 2011 ML350 with 92K miles, i think my oil level is increasing, but i don't know why. car runs really smooth.

I will add i used a 3/8" tube pushed onto a soap dispenser pump. I pumped out some of the oil about 1/2 a quart through the dipstick hole. did not smell of petrol or anything like that. I like my oil capacity to sit at just below full

 

My latest intel on oil level checking.....
when i check the oil level after the car has been sitting over night. it shows just about maximum level.
If i check the oil about 30 minutes after the engines was stopped, it shows about 3/4 to 7/8 full.
This obviously suggest that it takes some time for the oil to drain back to the sump.
I use 0W-40 oil which is almost as viscous as water when cold, but thickens up when the engine gets hotter.
so all in all i think the old girl is doing just fine for so many miles

 

Excellent brief definition of viscosity.
(edit add)
Particularly multi vis.

 

The oil does not thicken up when hotter. Something to consider when running ultra thin oil in an extremely expensive engine.
You couldn't pay me to put 0W oil in any engine of any kind. I do have a qt of 0W, but I use it to lube door hinges, my pocket knife, etc.