[Jasper]

I've read a bunch of posts - here, on Edmunds, and other forums - regarding the multi-displacement system and oil. But I haven't seen an explanation of how the two are related, even after searching, other than a passing mention that one of the criteria/data points in the MDS logic ladders might be the oil pressure. I've seen people advising for/against synthetics, etc. because "it's critical with MDS."

My questions: Does anyone have a definitive answer on how oil selection directly relates to the MDS? For example, if the dealer installs the wrong viscosity, how does the MDS "know" this? Is there a "viscosity sensor" somewhere related to the MDS?

I'm confused...

 

[joey]

Don't know about synthetic 5W-20 and MDS, but per this TSB, anything other than 5W-20 will mess up the MDS.
A 10% to 20% drop in gas mileage after an oil change would be an indicator the wrong oil was used.

 

[arnoldw]

MDS disables the hydraulic lifters. There would be small passageways/tight tolerences. I'm sure it would be oil pressure sensitive.

 

[II kings 9:20]

It is about flow and pressure, this dead horse has been beaten many times but again 5w20 oil is 5w20 oil, synthetic is not thinner. It resists thermal breakdown, sludge formation, and gelling in extreme cold but is not thinner. If I recall correctly, the manual specifically states synthetic oil is approved as long as it meets the API grade and is 5w20. Moral of the story, use what the factory calls for (5w20) and fielder's choice on synthetic vs conventional.

 

[Alsmag]

I just recently took my car in for its first oil change. I requested that they use synthetic, but the service guy told me that they couldn't due to needing "certain" oil since it was MDS.

I call bullsh*t.

 

[vvv90]

I just recently took my car in for its first oil change. I requested that they use synthetic, but the service guy told me that they couldn't due to needing "certain" oil since it was MDS.

I call bullsh*t.

:bs2: .....

 

[Jasper]

My concern was less about synthetic versus dino (I've read all 24 pages of the "sticky" thread on THAT topic - I should not have mentioned it in my first post, and I apologize :wave: ), but more a curiosity about HOW the MDS "knows" that the engine is pumping the wrong weight/viscosity.

If you use 10w30 instead of 5w20, is it the pressure difference at a specific RPM that mucks up the MDS engagement? And, if so, providing that there's been no coking in the passages, when you swap for the proper weight, does the MDS come back "alive?"

Not at all trying to go against the umpteen manual / TSB references - just wondering WHY they are so adamant about it? Is it "once you use 10w30, your MDS is dead as a hammer for the rest of your life?"

Hmmm.... :33:

 

[arnoldw]

I think it's really much ado about nothing. It wouldn't surprise me if you put in 20-50 and it still worked. I remember something about when they were developing these engines. They tested them for something like a million or 10 million miles or so, under all kinds of harsh conditions and decided on 5-20. Lots of other cars today also use 5-20 because it's thinner, there's less resistance, therefore better gas mileage.

 

[joey]

My concern was less about synthetic versus dino (I've read all 24 pages of the "sticky" thread on THAT topic - I should not have mentioned it in my first post, and I apologize :wave: ), but more a curiosity about HOW the MDS "knows" that the engine is pumping the wrong weight/viscosity.

If you use 10w30 instead of 5w20, is it the pressure difference at a specific RPM that mucks up the MDS engagement? And, if so, providing that there's been no coking in the passages, when you swap for the proper weight, does the MDS come back "alive?"

Not at all trying to go against the umpteen manual / TSB references - just wondering WHY they are so adamant about it? Is it "once you use 10w30, your MDS is dead as a hammer for the rest of your life?"

Hmmm.... :33:

Something to do with oil pressure. I doubt MDS is permanently dead after using wrong weight. Just switch back to 5W-20 and it probably works again.
Here is short blurb from here.
http://www.popularmechanics.com/automotive/auto_technology/1266926.html?page=4&c=y

DURABILITY, RELIABILITY, DRIVEABILITY
Naturally, Chrysler had to ensure robust MDS operation for proper performance, durability and customer satisfaction, among other criteria. So the new Hemi was tested with oil ranging from 10 to 50 weight at low and high temperatures and under a variety of pressures. Once satisfied, the engineers settled on 5W-20 grade, and the minimum and maximum oil pressure limits for cylinder deactivation and reactivation were established at 75 psi and 18 psi, respectively.
Switching from eight cylinders to four decreases the frequency but increases the amplitude of engine vibrations. So the techies had to come up with a solution. They found it in the form of a torsional torque converter damper acting on the turbine side, in combination with a moderate amount of torque converter slip--but not so much slip that it negates the fuel economy benefits of running on just four cylinders. Together these two strategies absorb the V4’s harsher firing pulses, making the cylinder-deactivation transition seamless.

 

[Jasper]

Thank you!!

joey - Thank you! That's exactly the information for which I was looking, and about which I wanted to learn!

Really appreciate the link and the lead - thanks! :wave:

 

[ricardo]

I do not know details, but mileage has slightly increased after the first oil change.