Mercedes and synthetic oil question

[daveh55et]

I have a problem/question about the use of synthetic oil in an slightly older Mercedes.

My father in-law has a 1997 E320, v6, bought used at 111K miles. It now has about 117K miles and last summer the "Low oil" warning started coming on even though the oil as checked manually was fine.

He finally hit upon a cure, don't use synthetic oil. I believe synthetic oil is specified in the owners manual.

Unfortunately I forgot and yesterday had the oil changed for him and had them put in synthetic, now the light is on again. Unfortunately I don't know what weight synthetic oil was used. There's no lifter noise, no bearing noise as far as I can tell it is running fine.

I have an appointment tomorrow to have the oil changed again, to non synthetic.

Here's my questions: What is triggering the low oil light? Low oil pressure because synthetic is easier to pump? Is the oil to "clean" and does not register on some kind of optical sensor? Is there any problem running non synthetic oil?

I hesitate to take it to be scanned by the dealer, $100 to tell us "it thinks the oil is low".

Thanks.

 

[Unotec]

I am unsure what the problem is, but I do recall hearing in the very long past that once you changed from synthetic to non synthetic, there was no going back. I cannot remember the reason, though

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[evelrod]

My guess is the dealer put the std oil that was 'in the barrel' in the car. The low oil pressure at idle could be a result of the lower viscosity and not necessarily the use of synthetic oil. My guess is that at only 117k miles, that should be the appropriate lube for the car unless there is some underlying reason(failure?)for the light...

http://www.whnet.com/4x4/oil.html

A Mercedes with 100,000 miles on the clock is still "new" in my book. My wife's Lincoln has 158,000 and is still on 5W-20 synthetic and uses no oil between changes! Perhaps you have purchased a car that is the victim of abuse or an unscrupulous dealer that 'turned the clock back'?

Rod

 

[Artisi]

I would suspect it's viscosity - you need to check what the viscosity is at the running temp.

 

[kchan711]

Most oil level sensors simply measure level through multiple means (float to contact, potential, etc). I would imagine your oil level sensor works on the same principal, and it may very well be shot.

Mixing between synthetic oil or standard oil makes no difference. Technically, it will always be in a mixed state knowing the fact you can never completely remove all the oil out of an engine simply at oil change time, albeit the percentage of removed oil will drop each oil change.

Now some engines require synthetic for different reasons such as better thermal breakdown qualities, clearance protection, friction reduction, heat transfer capabilities and so on. Generally, the higher the performance (and newer the car), the more likely it will require synthetic oil. Newer, higher performance cars have closer tolerances, run at higher temperatures and push the engine to greater extremes compared to an older car of similar engine size.

Besides, it makes for one hell of a marketing push; "Mobil 1 Synthetic, the Official Oil of NASCAR".

Kyle Chandler

http://www.chiefengineering.net

 

[SomptingGuy]

I was hooked, right up until the final word.

- Steve

 

[kchan711]

hahaha... Well, if it makes you feel any better, it's also used in every other race league. I just think NASCAR paid the most to put their name on the container.

Kyle Chandler

http://www.chiefengineering.net

 

[daveh55et]

Just FYI to close this out, I had it changed to non synthetic and all is well. They checked the oil pressure on the synthetic, it was fine. <shrug>

 

[kchan711]

That's interesting. It would be nice to talk to a Mercedes engineer to really disclose the reasons for the problem. Anywho, I'm glad the car is running accordingly.

Kyle Chandler

http://www.chiefengineering.net

 

[patprimmer]

I know it's to late now, but if it is truly an oil level gauge and not an oil pressure gauge then a few things spring to mind.

If it were a float type gauge the type of oil could have no influence except for a slight difference in float height if there is a difference in SG.

If it were an electronic sensor type gauge, then a change in the conductivity or polar nature of the oil might upset it, so I expect that is the answer.

If the oil level is showing low, but known to be OK, just pull the wire from the indicator and occasionally check the dipstick. Problem solved.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[swall]

Pat--interesting that you brought up the oil conductivity thing. I just changed the factory fill oil in my new GM truck and put in Mobil 1. About a week later, I get an online diagnostic from Onstar telling me my oil life remaining is 80%. I thought that kind of odd and had the thought about a conductivity difference confusing the oil life sensor.

 

[dgallup]

A piece of tape over the light is the true redneck solution.

 

[SincoTC]

I'm just getting a '99 E320 112K, so I am looking at its service history and this thread with interest.

These articles may be of interest:

http://ezinearticles.com/?Oil-Monitoring-Systems---Friend-or-Foe?&id=1041543

http://www.mvfri.org/Contracts/Final Reports/Chilworth_final.pdf

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

SW2007x64 SP3.0 Pentium P4 3.6Ghz, 4Gb Ram ATI FireGL V7100 Driver: 8.323.0.0
SW2009x32 SP1.0 Pentium P4 3.6Ghz, 2Gb Ram NVIDIA Quadro FX 500 Driver: 6.14.11.7751

 

[romke]

you should have no problem with this car using a 10W-xx synthetic engine oil. when using a 5W-xx or a 0W-xx the oil check light might come on when idling. as far as i am aware the oil sensor is still a pressure sensor on this engine - which means that it sees a lower pressure due to the fact that the oil is easier to pump and thus the oilpump does not build up so much pressure. if all is mechanically correct, two items may cause the oil warning light: a faulty sensor (it is not exactly a precision instrument) or low idle - which would be unusual. as long as the light only comes on when idling and immediately extinguishes when the rpm is raised to say 150 rpm above idle, there is no reason for conccern.

 

[daveh55et]

A couple of additional notes:

Once the warning comes up it stays up until a shutdown and restart. It also doesn't come on at idle but instead during normal driving. Finally the message completely obliterates the mileage information. And I'd aslo wager that if the wire was disconnected there would be a different area.

As an aside, which is not on topic, but in general I find that Mercedes spent needless time on "fussy" engineering. This being an example. Why not just leave it at low oil pressure? Real time oil quality monitoring? What's the point?

 

[izzmus]

If any of the OEMs do real time oil *analysis* then that's news to me. I am not familiar with Mercedes specifically (other than a blurb that the latest models do not even have dipsticks) but GM does not actually check the oil's quality. The older vehicles went on a strict mileage interval for the maintenance reminder, the newer ones have an internal algorithm based on driving conditions (coolant temps normally seen, trip cycles, etc.)

80% remaining is about 2000 miles for a lot of highway use, or something abusive after resetting the maintenance reminder light.

 

[romke]

if the vehicle is equipped with the Mercedes "Assyst" system, a few items are more or less continuously checked: engine rpm, load, oiltemp, watertemp, oillevel, dielectric constant of the oil, vehicle speed and time. The oiltemp, oillevel and dielectric constant are generated by the oilsensor. al this info together is then processed the output being time/mileage unto the next service interval, and oil level. also a "oil refill bonus" is calculated which means that when you top up with fresh oil the oil drain interval may be extended due to the then changed dielectric constant. the only actual "oil analysis" element in this is the dielectric constant and it is in no way sufficient for calculating the most suitable drain interval. the other input variables (number of starts, driving speeds, temperatures) are processed on the basis of a more or less sophisticated algoritm developed together with a well known oilsupplier after doing lots of field en engine bench tests.

in your particular case either the sensor could be at fault or the software used. a mercedes repair shop should be capable to check both.