Piston Slap: Less Slap, More (oil) Control
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.
[Image: Shutterstock user COZ]
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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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.
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.