By on August 26, 2014
(photo courtesy: autozone.com)

(photo courtesy: autozone.com)

Pete writes:

Hey Sajeev, I got one for you.

Several engines nowadays are set up to operate on half their cylinders under light-load conditions. Would the design considerations for piston rings vary from those normally used for such cylinders that are only used part-time? The question arises in the context of a 2009 V6 Accord that is currently in the Honda dealer’s shop to have the piston rings replaced at the manufacturer’s expense to cure a continual oil consumption and spark plug fouling problem.

Sajeev answers:

We learned from a previous Piston Slap that General Motors answered your query:  the displacement-on-demand (DoD) 5.3L truck motor (and its sister, LS4-FTW?) needs new and redesigned piston rings to cut oil consumption in the four deactivated cylinders. The motors still (supposedly) performs as intended with strong compression from the compression rings, oil burning is only a shameful side effect. Not to make a molehill out of a mountain, but that’s it.

Or perhaps turn off DoD with a computer re-flash, since there’s no free lunch in this business: if you want fuel economy, buy a lighter, trimmer and smaller engined vehicle. But I digress…

Honda, operating under the same Laws of Physics (Thermodynamics?) has the same DoD problem. In theory, the design of the “oil control” piston rings is crucial: more info is in this insanely detailed article. Definitely great bedtime reading for the Pistonhead.

Honda’s Class Action lawsuit doesn’t seem to hurt Odyssey or Accord resale values, so dump it if you wish. Or regularly check your oil level and spark plug condition, doing so lets affected V6 Honda products live a long and happy-ish life. Heck, this much oil consumption (1-3 quarts per high mileage oil change) was once the norm (during old school 3000 mi intervals) and that’s without DoD’s inherent fuel savings.

But that fact remains: save fuel or save oil? Pick one, son.

 

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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34 Comments on “Piston Slap: Less Slap, More (oil) Control...”


  • avatar
    jmo

    ” 2009 V6 Accord that is currently in the Honda dealer’s shop to have the piston rings replaced”

    Obvious trolling, we all no no Honda has every broken down and 100% of all Honda’s ever made are still on the road.

    • 0 avatar
      bosozoku

      No, no, that only applies to the mythical pre-2000 Civics and Accords, each painstakingly hand-built in spotless Japanese clean rooms by Soichiro Honda himself. Their adamantium-lined cylinders and bearing races are the stuff of legend, passed down through the generations.

  • avatar

    Thanks Sajeev, I always wondered why my 2007 HEMI Magnum burned more oil than my 1979 Volvo 242. For me, the difference between 22mpg with the MDS and 18mpg without it (I had a programmer so I could turn it off) was too much, and just checked my oil once in a while like you should be doing anyway.

  • avatar
    raph

    Huh, I wonder what the root issue is with DOD engines and the oil consumption? Is it temperature related? Do these engines use very low tension rings ( piston rings are a major sours of parasitic loss in an engine )?

    I’ll have to check the link when I have more time.

  • avatar
    Aquineas

    I always wondered about DOD but I had a different question: Is there a difference in engine wear between the cylinders which are operational vs those that aren’t?

  • avatar
    autojim

    It is, in fact, a ring tension issue.

    Low-tension rings, in particular, rely on the pressure of the combustion gases to help force the rings into contact with the ring lands of the piston and the cylinder bore wall. Eliminate the combustion gas pressure by eliminating combustion, and the rings won’t seat as firmly and they won’t squeegee the oil off the bore walls as effectively.

    Also, more oil will remain in the compression ring lands, which eventually will add to carbon buildup as danio3834 points out.

    DOD systems are an interesting but somewhat flawed technology. At least they’re now mostly more reliable than the old V8-6-4 Cadillac engines.

    • 0 avatar

      You rock, Jim.

      • 0 avatar
        Windy

        Your last point about oil use back in the dark ages was most apt Sajeev.
        In 1971 I owned a jeep wagoneer that after breaking it in properly by the owners manual instructions and having the breaking oil changed at 1000 miles used about a quart every 1500 miles and had its winter change at every 3000 mile and its summer dusty dirt roads change at 3000 miles (and let’s not forget hitting about 20 spots with grease gun each time) .
        The way we accepted the required maintenance back then is often forgotten I recall back in the day of more porous rubber needing to top up air pressure in my tyres every other fill up.. And if you drop further back to my grandfathers day cars came with oiling systems on the dash where you pushed plungers to oil various components on the car… A bit further back and you walked about your motor with a long spout oil can like the engine driver of a steam locomotive before each trip and again when you stopped to fix your frequent flat tyres. ( I think the fact that they were still in the minority of road users 100 years ago and the horses had their shoes nailed on may have contributed to the large number of flats suffered at the time)

        I am a bit amazed that the DOD engines work as well as they do… But then I had a friend with one of those Cadillac 8-6-4 engines back in the 70s so I have low baseline expectation for them.

        On the off topic subject of tyre life I had a pal in the 50s who had a gadget for his ford v8 flathead that fitted between the spark plug and the cylinder that provided compressed fuel/air via a hose for topping up your pressure… I wonder if any of them had explosive consequences from their use.

    • 0 avatar
      Carlson Fan

      The low tension rings don’t seem to be a problem until you have the carbon build-up. We didn’t have consumption problems with our AFM 5.3 in our ’07 Tahoe until it was almost 4 years old with a little over 50K. So for the first 7 oil changes it wasn’t using a quart in 7500 miles. At 97K it is using a quart every 2K miles.

  • avatar
    -Nate

    Fascinating .

    -Nate

  • avatar
    LeadHead

    I wonder what Chrysler did to control the oil consumption with their DoD system? I know some Hemis tend to have slightly high oil consumption, but it seems no where near the issues GM had with theirs.

  • avatar
    fincar1

    I’m the OP, and I’m happy to say that my 2009 V6 Accord has gone two or three thousand miles since the piston rings were replaced, and the car is behaving more like I’m used to with Hondas, and hasn’t used any oil.

    I had been changing the oil when the minder showed 5-10%; I plan on more frequent oil changes from now on.

    I found out by reading Honda forums that there’s some reason having to do with the way Honda accounts for warranty work that they hold off until the car has 60k miles on it before they change the rings. In our case, after having had rear-bank spark plugs replaced three times in 50k miles, along with quite non-Honda-like oil consumption, we were seriously discussing moving on to another car. Now the chances are that we’ll hold it and see how it goes.

  • avatar
    jmolyneaux

    Nice article by the Honda engineers who developed the newest version of the 3.5L V6 with Variable Cylinder Management (VCM) going into the new 2014 RLX and 2015 Acura TLX. Includes some new technology used to dynamically control inner cylinder wall diameter on these engines, other friction reduction items, VCM improvements, etc.

    Summary here:

    https://www.hondarandd.jp/index.php

    https://www.hondarandd.jp/summary.php?sid=38&lang=en

    You need to create an account with Honda R&D to get the actual PDF copy of the technical papers, but they are available to anyone.

    jm

  • avatar

    Does this issue have any implications for newer cars where the cylinders basically shut off when you’re coasting?

  • avatar
    golden2husky

    Has the GM LSX DOD issues been solved? I experienced 32 MPG in my C7 with a totally green engine in V4 mode. I’d hate to bypass the system and give up that efficiency but the cost of ring changes is way more than the gas…

  • avatar
    Truckducken

    Do any of these DOD systems shut off cylinders in a less uniform pattern so that each cylinder fires occasionally? Seems like this could slow the carbon buildup by reducing the residence time of oil between the rings.

    • 0 avatar
      AFX

      “Do any of these DOD systems shut off cylinders in a less uniform pattern so that each cylinder fires occasionally ?”

      You could try scrounging the junkyard for some old used sparkplug wires, that might do the trick.

      On the downside your engine would probably sound like a WW-1 biplane at idle.

    • 0 avatar
      wmba

      Not in production yet, but I believe it is a German supplier company (Continental?) who have come up with a system for a 3 cylinder engine. Requires heroic camshaft design, so even a 4 cylinder inline is too complicated. Was reported on here on TTAC just six or eight weeks ago.

      Basically, for a 4stroke cycle in VCM mode, for every two revolutions, it fires two cylinders, then indexes for the next two revs. So firing order is 1,2, then 1,3, then 2,3. Repeat. Keeps all cylinders hot.

    • 0 avatar
      05lgt

      I wonder if anyone else used to run an MSD soft touch rev limiter. Props to MSD for saving me from I don’t know how many rebuilds.

  • avatar
    87 Morgan

    It is my understanding the issue with the GM LSX motors has been resolved post 09′. I had the rings replaced on my 08′ suburban under warranty. I only noticed the consumption issue when driving home from the mountains. You get about ten mpg on the way up and 30 or better on the way home. So, the motor operates in 4 cylinder mode most of the way down the hill, about 90 miles. I would burn close to a half quart during this trip.

    I was told, as I did not watch the repair, the rings were replaced and a shroud was installed over the oil pump/suction mechanism to alleviate oil sloshing up into the cylinder wall and seeping past the rings.

    I can only surmise it is a heat issue, as the deactivated cylinders cool from no detonation the rings shrink allowing oil by.

    I will add that this type of issue is beyond my IQ though, so I could be way off. The moral of the story for me is the issue has been resolved and at 74k miles the 5.3 runs like new. So I am happy.

    • 0 avatar
      AFX

      “…the 5.3 runs like new”.

      You say that like it’s a GOOD thing…LOL !.

      • 0 avatar
        87 Morgan

        I know, I know.

        Gods honest truth..the most reliable cars I have ever owned were GM and Chrysler products, as in zero to few repairs which were warranty items.

        Now, give me a Subaru, Nisasan Maxima or a Mazda and I will be the shops best friend. I am the only person I know who can by a reputed reliable car and have a nightmare ownership. Mopar on the other hand, 7 years of problem free driving. Go figure.

        • 0 avatar
          AFX

          I think it was a comment in a Car & Driver article years ago that said GM cars run bad for longer than most cars run at all.

          • 0 avatar
            highdesertcat

            AFX, it may have been a comment in a C&D article years ago, but I remember that old saying from back in the sixties.

            Back then it was, “GM runs badly longer than most do at all.”

            And I bought mostly GM, new, until 2008.

  • avatar
    AFX

    GM has had several different technologies over the years for deactivating cylinders while driving. Their 1st system was mechanical in nature, and worked off the principal of blown headgaskets. The 2nd system they used was electrical, and it consisted of blown ignition coil packs. Some later high tech GM engines, such as the Quad-4, used both blown headgaskets and blown coilpacks to deactivate cylinders while driving.

    BTW, “Displacement-on-demand” is a marketing catchphrase originally developed by the Germans, by a German U-boat commander.

  • avatar
    Carrera

    My wife’s 2006 Pilot has been using 1 qt of fully synthetic Mobil 1 every 10,000 since new. Right now, just passed 100k, running as strong as ever, no complaints. Only once I let it go almost 1qt low, but since it was on the 15k miles fancy Mobil 1, I haven’t lost too much sleep over it. Oh, and for the naysayers, the transmission hasn’t grenaded yet in any of my high mileage Hondas…and I am on my 8 or 9th…all taken to over 100k miles. I had a poor 1989 Accord which I bought very used with 165k on it. The previous idiot owners towed heavy stuff with it although those weren’t supposed to tow at all. For 500 bucks with the AC working, I couldn’t say no though. I used it for one year and put about 15k on it. The internal, non serviceable trans filter was so filled with crud that once the car just ran out of steam while the engine was still running fine. I let it settle for 5 min and it was fine after that. The transmission mechanic explained that fluid couldn’t go between chambers due to filthy filter due to abuse, but not worth fixing at that point. Drove it to 180k miles and sold it for 400 bucks.


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