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Could engines run on 1 cylinder while idling to save fuel? And then either each "idle" session alternate a different cylinder so wear and tear is even, or change the active cylinder periodically throughout an idle session (i.e every 1 minute idle, change the singular active cylinder). I realize that this is probably pointless with modern start / stop features on many newer engines, but why wasn't my idea possible before we came up with the tech to enable modern start / stop on engines?

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    $\begingroup$ Cylinder deactivation has been done several times with autos. It ranged from being a complete failure to a waist of time. There may be some bigger diesels that have cylinder deactivation that get better results. It apparently can reduce emissions at low load. $\endgroup$
    – Phil Sweet
    Mar 6 at 18:14
  • $\begingroup$ 14.2.1.2 Low load optimization (optional) During low load operation in gas mode (below 25% load), up to one third of the cylinders can be deactivated. The remaining cylinders will be operating at a higher load, thus more efficiently. Only the fuel will be deactivated, the valve train is operational in all cylinders and air is pumped through the deactivated cylinders. The deactivation is circulated between the cylinders in order to balance the thermal load.cdn.wartsila.com/docs/default-source/product-files/engines/… $\endgroup$
    – Phil Sweet
    Mar 6 at 18:22
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    $\begingroup$ Cadillac (iirc) did it for one of their big v8 engines - even tested it in the desert... $\endgroup$
    – Solar Mike
    Mar 6 at 18:25
  • $\begingroup$ Make-or-break engines didn't have a throttle plate. Cylinder deactivation was all they had. That and a monster flywheel. $\endgroup$
    – Phil Sweet
    Mar 6 at 18:25
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    $\begingroup$ @SolarMike Cadilac 8-6-4 $\endgroup$
    – Phil Sweet
    Mar 6 at 18:31
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If you shut off the ignition for the cylinder you wish to disable, the action of the piston rising and falling in the cylinder (with no combustion) will tend to load the combustion chamber with motor oil, which then fouls the spark plug- so that when you want to turn that cylinder back on, it refuses to fire.

That puts the driver in a perilous situation, if (s)he were trying to pass another car on the highway. You are cruising along with cylinders idled, then you pull out to pass, step on the gas- and instead of the idled cylinders suddenly "waking up", the engine stumbles, bucks, misfires and smokes. Yikes!

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  • $\begingroup$ I'm guessing in normal operation, the combustion part of the cycle is enough to burn off any motor oil in the combustion chamber before it can accumulate and foul the spark plugs? $\endgroup$
    – cwille97
    Mar 6 at 19:54
  • $\begingroup$ yes yes, that is correct- and the better the ring seals are in the pistons, the less oil gets pulled up & burned this way. $\endgroup$ Mar 6 at 20:07

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