shamrode

I know that this has been churned over many times because I have been reading all the posts. Still not clear. Some say to check oil when cold (overnight) while others say to check 5 minutes after shut down. Some say that hot reading is higher up on dipstick than cold reading. This can't be true because there still may be oil in the engine and not in the sump while engine is warm. Really interesting; don't check oil in the morning because it doesn't stick to the dipstick when cold. True? I haven't driven my car in a week. Checked oil when dead cold as it was at the bottom mark. I added about a liter gradually but it never registered on the dipstick until I let it sit there for a minute. Huh....cold oil doesn't stick to dipstick?

Mort

When you add cold oil to a cold engine it just takes a minute to flow to the sump. To get a reading on the dipstick you need to pull it out and wipe it off then reinsert it for a few seconds and pull it again to get a reading. Then the oil gets on the dipstick tube from the dipstick and then back onto the dipstick when you pull it again. Makes it difficult to see the actual level when you pull it again. Look for the line where the oil is solid across the full width of the dipstick and check on both sides of the dipstick. When I checked the oil in our GLK 350 it would have no oil on the dipstick at all until I reinserted it. Needed to break the seal at the top of the dipstick I guess as crankcase vacuum must have sucked the dipstick dry. Just a theory. I generally check my oil level cold in the morning after sitting for the night. If you check your oil when the engine is at normal operating temperature, turn your engine off and wait approximately five minutes before checking.

cornerjunkie

I choose to check it after 5 mins and continue to do it like this. My suggestion is whatever you choose to do, stick with it so that you get the consistent readings you're looking for.

looney100

We are talking about the engine oil, right? If so, it really doesn't matter you just want the oil level between the min and max lines, and you've got a fair bit if room between the such that the expansion of the oil due heat isn't going to affect things enough to matter.

Given the massive oil capacity in these engines, a half litre either way isn't going to matter. My suggestion is to fill to the midpoint when doing a change, and add a litre if you get to the min. line.

As stated earlier, the more important thing is making sure the oil has time to reach the pan once you've added some before taking a reading.

Diabolis

Hot oil is a lot thinner than cold oil and will flow / drain back to the sump easier - but keep in mind that after you've run your engine, the oil is sprayed everywhere and that it takes some time for it to collect back down into the sump. I usualy check mine when it's hot but the engine has been shut off for at least 10 minutes... which will produce exactly the same reading the following morning when the car has been sitting overnight and the oil is cold.

m a x i m u s

IMO, this is the wonkiest car I've ever owned as far as checking oil level goes. Whenever I add, it takes a very long time for it to reach the pan so that it registers on the dip stick. Oh well.

Diabolis

^ ...which is exactly why I like to check mine when it's hot but has had enough time to settle in the pan.

shamrode

When hot does it take more than five minutes to reach the pan?

Mort

MB recommends waiting approximately 5 minutes, after switching the engine off, before checking the oil level when the engine is at normal operating temperatures.

Diabolis

I am pulling these numbers out of my a$$ for illustration purposes only, but after 5 minutes maybe 95.8% of the oil will have drained back into the pan. After 10 minutes 97.3% will have made it back down, and overnight an additional 0.4% will have collected back in the sump. If none of the oil adhered to the surface of the various engine bits and 100% of it made it back into the pan, your engine would seize the very next time you try to start it.

So - five minutes is OK, ten is a little better if you have the time and don't want to burn yourself as badly when you wipe down the dipstick, and overnight works just as well with almost zero risk of thermally induced injuries.