Piston Slap: Less Slap, More (oil) Control

(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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