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Discussion Starter · #1 ·
Hello! I am sure the good people on this forum will be able to answer this question once and for all, so thank you in advance! I have a 2017 RAM 1500 5.7 Hemi. I love this truck! I drive back and forth between states every few months (1300 miles one way). Most of the time my truck will show "ECO" mode and my gas mileage is phenomenal! However, both my brother and my mom's neighbor have told me that ECO mode is merely a marketing gimmick to get sales and that eventually my engine will "blow up" and need to be replaced because the 4 cylinders that aren't engaged when in ECO mode are not getting "lubed." Is there any truth to this? My brother says there are ways to permanently disable this mode and that I should do it before I "ruin my engine." Right now I have 13,000 miles on it. Thoughts very much appreciated, thank you!!
 

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Short answer:
The system works and works well. Just drive the truck and dont worry about it :)

Although it often occurs at more or less the same time, cylinder deactivation occurs independently of the "eco" light coming on - that light simply means you're driving in a fuel efficient manor.

Long answer:
MDS is a system that temporarily deactivates 4 of the engine’s 8 cylinders under low load conditions to increase combustion efficiency, and therefore increase fuel economy. The system consists of 4 MDS solenoids, dedicated oil passages within the block, a special camshaft with lobes to allow MDS’s operation,
and special lifters on the cylinders that are deactivated (8 in total). The PCM uses oxygen sensor readings to confirm the cylinders are actually deactivated or reactivated, and constantly monitors its performance, taking into account pressure differences based on oil temperature readings.

When the PCM determines conditions are appropriate, it commands the MDS solenoids to engage, one at a time, in the order 1, 4, 6, and 7. The solenoids divert oil flow through dedicated passages inside the engine block into the lifters of those cylinders. Those cylinders use special lifters that have
“disconnecting” or locking pins inside of them. When oil pressure compresses the locking pin, it prevents the lifter’s push rod from moving up by decoupling its motion from the camshaft lobes, and thus “deactivating” the cylinder. The transition occurs within fractions of a second, and is closely monitored
by the PCM.

The cylinders are deactivated during their compression stroke, where both the exhaust and intake valve are closed. Instead of exiting through the exhaust valve, the combustion gas remains trapped inside the cylinder, where it is constantly recompressed until the cylinders are reactivated. Ignition still
occurs in the deactivated cylinders so that all spark plugs wear evenly.

Cylinders are reactivated in the same order. Once reactivated, the exhaust valve opens, allowing the gases to finally escape, and the otto cycle returns to normal.

At no point is anything being starved of oil while the system is engaged. In fact, I theorize problems could occur if the system *isnt* used for long periods of time, as it could cause the locking pins inside the MDS lifters to stick.
 

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Sorry to say but your brother and mom's neighbor are misinformed.


I do have a question for you though, if you don't mind.
Do you tend to keep your vehicles for a fairly long time?
You are putting a bunch of miles on quickly and will probably go through the factory warranty fairly quickly. Ram does offer a Lifetime/unlimited miles/$100 deductible per visit extended warranty that you can buy for about $2700 or so online.
The $100 per visit is nice, so if you have a few things that need done, it is only $100 as opposed to $100 per occurrence. It basically extends the 3/36 bumper to bumper warranty for life.

A lot of people are unaware of this and it can be peace of mind if you keep your truck for a long time or miles. Just a FYI.
 

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HAHA this again? Get your popcorn ready...

Lone Dutch covered it...spot on!

AND thanks for the laugh, your bro is hilarious! Blow up due to MDS? Make sure he replaces your



while he is at it :att:
 

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Rams have had MDS since 2005 and I don't see them blowing up.
 

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They're wrong.
You can disable the Eco light in the settings for the truck, bbut as mentioned, it is independant of the MDS. You can disable MDS with tuners / programmers and by manually selecting 8th gear, or any gear for that matter, with the +/- gear selectors each time you start the truck.
 

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Discussion Starter · #8 ·
Thank you!!

You guys are all great..and hilarious! Thank you so much, that gives me peace of mind! Love the headlight fluid graphic!!!:smileup: Yes I do tend to keep my vehicles a long time, especially will with this one as I really love everything about it. I bought it with 8000 miles on it and the dealership gave me that 100,000 warranty automatically. They said they do that for all their used trucks but I will check into it to be sure it is the same one. That other warranty pacofortacos mentioned sounds smart! Thanks again everyone for all your help!
 

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You guys are all great..and hilarious! Thank you so much, that gives me peace of mind! Love the headlight fluid graphic!!!:smileup: Yes I do tend to keep my vehicles a long time, especially will with this one as I really love everything about it. I bought it with 8000 miles on it and the dealership gave me that 100,000 warranty automatically. They said they do that for all their used trucks but I will check into it to be sure it is the same one. That other warranty pacofortacos mentioned sounds smart! Thanks again everyone for all your help!
Ask a couple people and you will get different responses, but I would recommend a Catch Can for the unused/"extra" oil...it catches the oil from the PCV valve prior to entering back into the engine (this is for emissions purposes). I have had one on 3 HEMI's now and highly recommend getting one. IMO it cannot be great for all of that oil to coat the inside of the intake manifold. Had mine on for almost 5k miles and it has saved 6-7 ounces of oil from going back in.
 

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First thing you should do is sell some headlight fluid to your brother and mom's neighbor. They seem dumb enough to maybe buy from you on a regular basis. Be sure to jack the price up each time, citing high demand and low supply.

I guess you figured out that ECO and MDS are not the same thing. ECO just means your driving economically (not a mode or setting, just a "feel-good" light) and MDS deactivates 4 cylinders under certain conditions when the power isn't needed. Often times ECO and Cyliner deactivation happen at the same time, but they are not interconnected in ANY way. I have this system on both a Challenger and a RAM 1500 and it works great. Most people who want to deactivate the MDS just don't like how their exhaust sounds when the engine is only running on 4 cylinders. No really good reason to deactivate it. You mash the gas, and you get all 8 when you need them.
 

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Lone Dutch hit the nail on the head with his description-in fact the MDS lifters get MORE oil pressure when the cylinders are deactivated, as it is the oil pressure that keeps the pins driven into the lifters and the valves deactivated.

MDS has been in Hemi Rams since 2006 (I believe it appeared in 2005 in the Hemi cars chillin) and is a pretty well sorted out system. I know GM had issues with their cylinder deactivation and excessive oil consumption but I believe they got that sorted out too-some guys were getting new short blocks under warranty for that. I don't have personal experience with Chevy's DOD (displacement on demand-their name for cylinder deactivation) though.

Supposedly the Honda cylinder deactivation system had oil consumption issues too, though my mom's 2006 Odyssey with the cylinder deactivation V6 hasn't had any such issues and is nearing 190,000 miles.

Anyway, catch cans really don't have anything to do with MDS
 

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Anyway, catch cans really don't have anything to do with MDS
Has nothing to do with MDS...just provided another item to discuss with the family and would be interested to hear their take on the matter.

A CC may "blow" the engine up as well :SHOCKED:
 

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A CC may "blow" the engine up as well :SHOCKED:
No it won't. They aren't necessary on a naturally aspirated setup but they aren't harmful either
 

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Discussion Starter · #14 ·
I knew I would get some straight answers here, thanks guys! 18RAM, is that catch can something I could install or would it need to be done by a mechanic?
 

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If you can open the hood and maybe turn a wrench, then you could install it - especially the slightly more expensive ones that come with everything needed and good quality parts.
A lot of the cheaper units are ok, but don't have a bracket and/or come with a really inferior hose.


The only catch to a catch can :) is you do need to empty it regularly, you do not want to install and forget about it!
You are better off with no catch can than a forgotten one - which besides cost is why Ram doesn't install them.
 

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I would check on the warranty they gave you, it might be an in house powertrain only warranty - which while better than nothing, often requires you to only get repairs there and require you to have regular maintenance done there.
The FCA (Ram) extended warranty I mentioned is good at any FCA dealer and only maintenance records are required.
 

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Curious to know what happens to the gasoline when those four cylinders are activated by MDS. Is there also a solenoid to block the fuel. Also how can you tell if the truck has MDS?
 

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To me the "ECO" light is nothing more than a modern vacuum gauge. Remember them? I would almost bet you could put the trans in "8" to keep all 8 cylinders firing, hit the cruise at 55MPH and the "ECO" light would still come on.
 

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I knew I would get some straight answers here, thanks guys! 18RAM, is that catch can something I could install or would it need to be done by a mechanic?
Yes, it would be a 1 or 2 /10 on difficulty to install...very easy in our large engine bays! Maybe 20-30 mins

You need to empty it every 1-2k miles, but depending on the engine and usage, you could double that...the one I got has a spicket at the bottom to let it out...others twist of the bottom (can get messy)

No it won't. They aren't necessary on a naturally aspirated setup but they aren't harmful either
That was completely sarcastic, like the Headlight Fluid :gy:
 

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Richard66, The fuel injectors are shut off when the ECU goes into "4" cylinder mode.
 
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