When I turn on my car, stop at a light, or just have it in park it hovers around 750 rpm (my older car sat at like 1-1.2k rpm). But why? It’s not moving the car or anything. I know some modern cars turn off the engine if it idles for too long but that doesn’t really explain why. Also when I coast on the highway it will idle at even higher rpm’s. I would have expected the automatic transmission to shift down when it’s not applying any acceleration.
Furthermore, do electric engines idle at a rpm? If not does this make electric cars more energy efficient?
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An engine needs to be at a minimum regime to run continuously. There are losses from friction, etc. and to be able to go when you want it to. If you get below that, the engine will stall and you’d have to restart it manually.
Regarding going on the highway, your engine isn’t idle. It’s running at the RPM it needs to keep your speed constant. A transmission has limits in the gear ratios it has. You’re basically in the gear with the most fuel efficient ratio already, so you can’t shift to a more efficient gear.
By the way, when accelerating, the transmissions downshifts to gear ratios that are not as fuel efficient, but will give you better acceleration.
As for electric, they are a completely different beast in how they operate. It’s no longer internal combustion, it’s coils of wires and magnets. They don’t idle like an internal combustion engine would.
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