As you CDI owners may know, you can measure the oil level not merely the way the manual tells you to (reading OK, or add a quart, etc.), but you can get a reading that is precise to the tenth of a quart. But as I've done it recently (trying to figure out if I'm using any oil), I've gotten inconsistent measurements, ranging from 6.7 quarts to 6.9 quarts, or a 6 oz. range. Measurement is always taken at the same spot on the driveway, always after the car has been brought up to operating temperature, and always after plenty of time has been allowed for oil to drip into the pan.

I don't understand how, after sitting overnight, it can read 6.7 but then, after sitting for only two hours, it can read 6.9.

Am I overlooking some variables? Or is the system just not all that accurate?

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

8 % change in volume from 0F to 200F. volumetric expansion might be part of the discrepancy.

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Check the oil after sitting overnight and don't start the car before checking, no use having oil drain back in the mix.

If the car sits longer than overnight ( like weeks ) , the oil filter can drain out raising the level in the pan.

Also, pull the stick and wait for any oil to run down the tube. If you have a really good dipstick seal, sometimes oil will pump up the tube skewing the result high. If the level is different on opposite sides of the stick, there is oil in the tube.

If you are extrapolating oil level between add and full in hopes of getting a X distance = Y volume, that only works if the square inches of the pan does not change between the two levels. A cone with the point facing down won't have a linear height to volume relationship.

Check oil every say 250 miles and plot from there. Checking every day generates too much data noise, you need long term values. And, pulling and wiping the stick will in of it's self reduce the amount of oil in the pan, it is slight but can affect results in more critical scientific tests.

I was going to rant about people, who don't know what they are talking about, responding to threads. But I decided not to.

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

Now, Greg, that's funnier than h#ll! When I read; "pull the dipstick up the tube," or somesuch, I was set up for your remark! God love ya, Greg!

Now, can you help me find a loaded up, always garaged, '06 CDI, with black interior, clean Carfax, and 24K or so miles on it?

shertex: I. think you missed a calling as an aeronautical engineer!? 🐣☉

I'll expand on the false oil level reading subject since that is the only point brought to light so far.

I said some engines as in "engines in general", it may or may not apply to the engine in question.

If an engine sits overnight and the stick is pulled without wiping, waiting a bit then reinserting, the reading may be inaccurate.

Some on other threads have said they can attach an oil sucker to the TOP of the dipstick tube and remove oil. This means that the end of the tube extends below oil level. Most engines are not set up this way, the tube ends above oil level so "pull the stick and wait" does not apply.

If the dipstick has a good o ring seal on top, there is now a trapped column of air that will affect oil readings until the stick is removed and oil level in the tube equalizes with the sump.

I have 2 engines that ,days after use, reliably give very high readings if I just pull the stick and smeared readings if I pull, wipe and check too soon. These are a 20 HP Kohler Vertical shaft and a regular push mower, both have dip stick tubes that extend below oil level and have very good dip stick o rings.

My International backhoe ( with a German Neuss engine ) has a combination oil fill / dip stick with a tube that extends below oil level, I'm pretty sure the reading is high after siting overnight after a run as well but I haven't checked the oil lately.


Also have a look at these:


handling notes on the Piper Pa28


Piper Oil Check:

Fact is that oil will often creep up the oil stick under certain cooling conditions. First removal of the day will often give a false high oil level reading. Failure to wipe stick and re-insert it for a new reading may cause pilot to depart with far less oil that believed.






From a Yahama 4 stroke outboard engine service bulletin, it addresses that just pulling the stick and checking will give an inaccurate reading.

Yamaha Four-Cycle Engine Oil Level Measurement - Moderated Discussion Areas


3. Remove the oil dipstick and wipe it with a clean, dry rag, then reinsert the dipstick.

4. Remove the oil dipstick again and check the oil level.

NOTE: It is very important to remove the dipstick twice before measuring. The dipstick tube is not vented and can result in the oil level inside the tube being much lower than inside the oil pan. Removing the dipstick allows the tube to vent and equalizes the level inside the tube with that of the oil pan.

97 SL320, the CDI does not have an oil dipstick.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

No dipstick is an entirely different situation all together. It is generally safe assumption that most engines have dipsticks. Knowing that yours does not is fine minutia that not everyone is going to know.

Regardless, what I had posted is valid for some engines equipped with a stick.

And I pose this. If others truly believe that I know nothing about what I speak, have the moderator ban me. . . .

You are questioning the Repeatability of the sensor so you need to take the readings also in a controlled manner like 15 minutes after shutdown to validate what's happening. I would think the sensor would have an accuracy of .1% or better but you are noting a 3% error suggesting measurement sampling error.

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10

I just came across the info copied below. Now be honest, are the people that say I know nothing aware of the info below? If they are, why didn't they offer this information to assist the original poster? Surely the info below would assist him in solving the oil level issue.

~~~~~~~~




W203 Engine Oil Dipstick? - Page 1 - Mercedes - PistonHeads

Saturday 10th March 2012
rocklandboy

Just recently ive had an issue with the oil measuring system on the wifes C class (W203 model) in that is has given me

false readings - not enough oil, then a warning sign saying too much after adding what the dash display told me to add,

then not enough 2 weeks later... Trying to avoid the cost of new oil level switch, a manual dipstick surely would be

the answer to such a simple fix?!?!?!

However, looking at the engine today, there appears to be a steel tube that goes down the engine sump with a red

blanking plug on the top. I am now wondering if there is a dipstick on the market to dip the oil manually - does

anybody know of such a thing? I've done the Google and Ebay search but all that comes up is transmission dipsticks....






Sunday 11th March 2012
yellowbentines

The tube with a blanking plug is for a MB workshop dipstick this gives exact oil measurements in mm, its a special tool

and is used for a number of different engines so is too long to actually keep in the tube.

The instrument cluster measure should work sufficiently but i would suggest to everyone when it says add 1l of oil add

0.5 and re-check, allways and 0.5l less than it says to avoid overfilling.



Saturday 17th March 2012
rocklandboy

Back and thank you for tips.... At long last and after loads of searching, i finally managed to locate an MB workshop

dipstick - hopefully now, i can measure the oil with assurances that the oil level is correct with added bonus of

seeing what the oil actually looks like between services as on my other cars... Basic stuff but invaluable i'd say!?!?!

Bunches of _workshop engine oil_ sticks for sale. ( these are not the same as 722.6 trans oil sticks.)

Mercedes Oil Dipstick | eBay

I'm still waiting to be banned. . . .

97 sl320.

you have nothing to prove.

you provide excellent information. thank you.

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JT20, thanks for the good words.

Still waiting for an answer as to why my detractors didn't offer the OP information that a workshop dip stick exists. Surely reading from an actual stick is more accurate than the oil pan sensor.