> Presence of oil is critical here as it creates conditions for hydrodynamic lubrication.

You can hear this effect in some vehicles at initial startup time for a few seconds. I know of certain Ford engines where it actually causes issues over time. The model years with auto start/stop have the worst of the cam rattle disease.

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LeifCarrotson a day ago | parent | next [-]

Auto start/stop isn't off for enough time for the oil to drain from the galleries and especially not out of the bearing journals.

It's the first few seconds after an engine has been off for hours (or worse, for potentially years) that are the problem.

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toxik a day ago | parent [-]

I thought it pretty well established that auto on/off is bad for the engine, as is intermittently turning off some cylinders as some do. Is that wrong?

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Toutouxc a day ago | parent | next [-]

I don’t think it’s pretty well established, there are cars that will happily stop and start the engine multiple times per minute, e.g. Toyota hybrids with their “HSD” drivetrain. It just requires some engineering.

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trhway a day ago | parent [-]

I don’t think Toyota engine does traction from low rpm. Electric motor does it, and moments later already well spinning engine gets the load.

Hearing regular start-stop on intersection gives me sorry feeling for the engine.

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kube-system 15 hours ago | parent [-]

Hybrids generally command the ICE to run when under higher loads or cold conditions, but they do get a bit of a break under low load conditions when they’re warmed up.

But they also start and stop way more than a gasoline-only car with stop-start. Because they stop and start repeatedly while driving too. Series hybrids even more so.

	▲	trhway 14 hours ago \| parent [-]
		>But they also start and stop way more than a gasoline-only car with stop-start. they do it very differently. My Prius never does that coughing sound that the start-stop engines frequently do. The powerful electric motor in Prius spins the engine to at least 1000rpm before fuel is injected. That way it is much easy on the engine and much more fuel efficient too.

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gomoboo 21 hours ago | parent | prev | next [-]

“While aggressive start cycles (>20 cycles per day) could lead to premature failure in the starter system of light- to medium-duty commercial fleet vehicles, modern fuel injection and engine control systems have eliminated any issues associated with drivers of typical light-duty vehicles turning the engine off while stationary for short periods and restarting the vehicles for <10 start events per day.” from https://publications.anl.gov/anlpubs/2015/05/115925.pdf

This paper seems to say that generally they aren’t a problem. I’ve only seen unsubstantiated claims that they are one.

	▲	bob1029 12 hours ago \| parent [-]
		This paper reads like a high school science fair project with zero treatment for the concern originally presented (oil system pressure transients).

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vel0city a day ago | parent | prev [-]

It sounds like you're talking more about systems that supposedly disengage some cylinders while the car is cruising. Some engines with that kind of technology have been known to damage cylinders for multitude of reasons.

That's very different from the start/stop feature they're talking about. That's about fully stopping the engine when you come to a complete stop like at a red light and then automatically starting again when you get off the brake.

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Toutouxc a day ago | parent | prev | next [-]

Note that that sentence is talking about the crankshaft bearings and their hydrodynamic lubrication, which is, well, elsewhere and separate from any cam rattle issues (including the cam phaser oil starvation that you might be referring to).

	▲	culopatin a day ago \| parent [-]
		Lifters also often drain while sitting and valve lash is greater at start until they get slapped a few times

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bluedino a day ago | parent | prev [-]

That's the timing chain tensioners losing oil pressure.