Engine Oil Level

[rf065]

To: Rf065 and BlackC55 - The 2 doubting Thomases:

If you are using synthetic oil please check your oil level first thing in the AM after an all night cooldown and then check it when hot and see if there is any difference.

Not having a dipstick makes this difficult, but if the engine is left for a longer period, then of course more oil will have drained back into the sump. That will not be the correct measure of your engine oil though.

Mercedes will tell you when to measure your oil, in my case for a 2005 CLK

"Before checking the engine oil level the following conditions for the vehicle should be met:

It should be parked on level ground

The engine should be switched off for at least five minutes if the engine was at normal operating temperature

The engine should be switched off for at least 30 minutes if the engine was not at operating temperature (if you only started the engine briefly)"

After 5 minutes when hot or 30 minutes when cold is the correct time to check the oil level. Obviously cold oil take longer to return from the top of the engine to the sump, but 30 minutes is sufficient. If you have a dipstick or electronic oil level check, it is calibrated to check the correct level only at these times. For this example, checking the oil after 30 seconds or 24 hours, will give a false reading.

Regarding the holes in the dipstick, it is impossible to prove your theory by just showing a picture of a dipstick tube. What about the dipstick itself? How tight a fit are they together? Where does the o ring sit in relation to the holes, are they still open or closed when the dipstick is in place. There could be any number of reasons for these holes other than the one you suggest.

Russ ( still a doubting thomas )

 

[rf065]

The top of the dipstick tube has an inside diameter about 5/8" and is 3/4" long below the upper vent hole. Just imagine the pressure developed by the bore and stroke of the top of the dipstick pushing the oil down the tube and giving a false reading if there were no vent holes in the tube above the oil level. The dipstick tube is for a"99 E300 Turbodiesel.

The pressure rise by inserting a dipstick in a tube is nothing compared to the pressure required to compress a liquid.
Liquids do not compress easily, unlike air. Inserting a dipstick would compress the air in the dipstick tube, not by a great deal and certainly not enough to compress maybe 6 litres of oil in the sump. The holes are most likely to equalise the pressure & stop the dipstick being pushed back out of the tube while driving along the road due the pressure below the dipstick being higher than the atmospheric pressure outside. It has nothing to do with the oil level reading on the dipstick. I think that theory is more likely than the one you suggest, although I still havn't saw the design of the dipstick itself, only the tube.

Russ