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At idle, it doesn't take that much fuel to keep the engine alive. Idle stops are more important for noise abatement and local toxic exhaust gas emissions - a lo

At idle, it doesn't take that much fuel to keep the engine alive. Idle stops are more important for noise abatement and local toxic exhaust gas emissions - a lot of exhaust gas treatment depends on the exhaust gas having a minimum amount of thermal energy. The downsides of idle stops are, however, that they tend to put a lot of load on the engine, especially from the lack of oil pressure at the very few first strokes [1], and that the low temperature deposits all kinds of gunk in the exhaust pipework instead of transporting it outwards. If you run an engine with idle stop, it really really is important to properly take care of the engine, including preventative maintenance and regular oil changes. [1] That is even more of an issue in large engine blocks, hence that high pitched noise you hear from ships and locomotives for a while before they start up - that is an ancilliary oil pump, priming the entire oil pipework until all air is gone and full oil pressure is present at all ports in the system.

dragontamer 1mo ago
Unless you have a hybrid vehicle, like the Prius. Which basically switches to electric during idle stops and barely has any downside.
SoftTalker 1mo ago
Yeah I disable idle stop on my cars, for exactly those reasons. If I'm going to be stopped for more than a minute or two, I'll let the engine idle so that temperatures can normalize, then shut it off manually. Back when turbochargers became common on passenger cars, there was even advice to be sure you let the engine idle for a minute or two before shutting it off, so that the turbocharger could cool. Otherwise the oil in the turbocharger would get baked into a goo. Modern synthetic oils, and turbochargers, handle this better today but I still like to give any hot spots a chance to cool off.
- tristor 1mo ago
  > Back when turbochargers became common on passenger cars, there was even advice to be sure you let the engine idle for a minute or two before shutting it off, so that the turbocharger could cool. Otherwise the oil in the turbocharger would get baked into a goo. Modern synthetic oils, and turbochargers, handle this better today but I still like to give any hot spots a chance to cool off. Yes, it was common to install a "turbo timer" that would leave the engine running at idle for a time after you shut off the ignition to let your turbo cool. I drive a 2024 factory turboed vehicle and it still recommends idling for 30 seconds to 2 minutes after parking before shutting the vehicle off and it continues running an electric cooling fan on a timer after you shut off the ignition. The same set of challenges still exist in 2026 as did in 1986 for a turbo, for the most part.
enragedcacti 1mo ago
> The downsides of idle stops are, however, that they tend to put a lot of load on the engine While I don't doubt that it seems like this is essentially a solved issue. Priuses are some of the most reliable, long-lasting cars out there despite experiencing considerably more start-stop cycles than a traditional ICE with start-stop would.
- mschuster91 1mo ago
  Up to 2022 the Prius' ICE barely had 70 kW of engine power, and (IIRC, take with a grain of salt) neither turbochargers nor compressors. The less capacity the engine has, the more abuse it can tolerate, and it likely was ridiculously overspecced in tolerances and thicknesses. In contrast, your 100 kW+ average vehicle? Probably built for maximum profit margins.
- mauvehaus 1mo ago
  A Prius isn't taking off from a stop under strictly ICE power. The electric motor in the transmission lowers the load on the ICE, certainly enough to let the engine oil pump generate operating pressure before it's really under load.
- toast0 1mo ago
  Hybrids likely have more engineering around the start-stop cycles than full ICEs with start-stop bolted on to meet emissions requirements. The prius style dual motor/generator planetary gear arangment avoids concerns about starter motor longevity. But the engines and how they're managed is tuned for their use case. I'm sure ICE with start-stop will get there eventually, but the automotive industry tends to learn to build reliable drivetrains through a history of failure. From my experience with a couple rental cars a year, on user experience, start-stop is all over the map from really annoying to noticable but unobtrusive ... I imagine how design challenges around lubrication are met is also all over the map.
  - enragedcacti 1mo ago
    > Hybrids likely have more engineering around the start-stop cycles than full ICEs with start-stop bolted on to meet emissions requirements. What evidence is there for this? The Prius was around for 12 years before Toyota brought their first production start-stop ICE to market, surely they (and other mfgs whose hybrids predate start-stop) didn't just throw away all of that knowledge to haphazardly "bolt on" a start-stop system. They didn't, which is why start-stop equipped card have things like low-friction coatings on their crankshaft bearings. > The prius style dual motor/generator planetary gear arangment avoids concerns about starter motor longevity Redesigned starter motors with improved longevity also avoid these concerns. In start-stop systems, the starter motor is a safety critical item and they are engineered to a much higher standard. As far as I can find, there's only one start-stop starter related recall in the US (Honda) and it wasn't even a mechanical issue. > From my experience with a couple rental cars a year, on user experience, start-stop is all over the map from really annoying to noticable but unobtrusive ... I imagine how design challenges around lubrication are met is also all over the map. I think this captures exactly why people fixate on these systems. They assume that because they can be janky to use (they often can be), that they must be jankily designed. I can't prove a negative, but I just haven't ever seen meaningful evidence that start-stop cars fail faster or fail in the ways critics suggest they should. Surely we would see some evidence of the extra spun bearings, sparkly oil, and premature starter replacements that this almost 20 year old tech has has wrought by now, right? The only evidence I've seen are slightly more expensive batteries needing to be replaced slightly more often.

dragontamer 1mo ago

Unless you have a hybrid vehicle, like the Prius. Which basically switches to electric during idle stops and barely has any downside.

SoftTalker 1mo ago

Yeah I disable idle stop on my cars, for exactly those reasons. If I'm going to be stopped for more than a minute or two, I'll let the engine idle so that temperatures can normalize, then shut it off manually. Back when turbochargers became common on passenger cars, there was even advice to be sure you let the engine idle for a minute or two before shutting it off, so that the turbocharger could cool. Otherwise the oil in the turbocharger would get baked into a goo. Modern synthetic oils, and turbochargers, handle this better today but I still like to give any hot spots a chance to cool off.

tristor 1mo ago
> Back when turbochargers became common on passenger cars, there was even advice to be sure you let the engine idle for a minute or two before shutting it off, so that the turbocharger could cool. Otherwise the oil in the turbocharger would get baked into a goo. Modern synthetic oils, and turbochargers, handle this better today but I still like to give any hot spots a chance to cool off. Yes, it was common to install a "turbo timer" that would leave the engine running at idle for a time after you shut off the ignition to let your turbo cool. I drive a 2024 factory turboed vehicle and it still recommends idling for 30 seconds to 2 minutes after parking before shutting the vehicle off and it continues running an electric cooling fan on a timer after you shut off the ignition. The same set of challenges still exist in 2026 as did in 1986 for a turbo, for the most part.

enragedcacti 1mo ago

> The downsides of idle stops are, however, that they tend to put a lot of load on the engine While I don't doubt that it seems like this is essentially a solved issue. Priuses are some of the most reliable, long-lasting cars out there despite experiencing considerably more start-stop cycles than a traditional ICE with start-stop would.

mschuster91 1mo ago
Up to 2022 the Prius' ICE barely had 70 kW of engine power, and (IIRC, take with a grain of salt) neither turbochargers nor compressors. The less capacity the engine has, the more abuse it can tolerate, and it likely was ridiculously overspecced in tolerances and thicknesses. In contrast, your 100 kW+ average vehicle? Probably built for maximum profit margins.
mauvehaus 1mo ago
A Prius isn't taking off from a stop under strictly ICE power. The electric motor in the transmission lowers the load on the ICE, certainly enough to let the engine oil pump generate operating pressure before it's really under load.
toast0 1mo ago
Hybrids likely have more engineering around the start-stop cycles than full ICEs with start-stop bolted on to meet emissions requirements. The prius style dual motor/generator planetary gear arangment avoids concerns about starter motor longevity. But the engines and how they're managed is tuned for their use case. I'm sure ICE with start-stop will get there eventually, but the automotive industry tends to learn to build reliable drivetrains through a history of failure. From my experience with a couple rental cars a year, on user experience, start-stop is all over the map from really annoying to noticable but unobtrusive ... I imagine how design challenges around lubrication are met is also all over the map.
- enragedcacti 1mo ago
  > Hybrids likely have more engineering around the start-stop cycles than full ICEs with start-stop bolted on to meet emissions requirements. What evidence is there for this? The Prius was around for 12 years before Toyota brought their first production start-stop ICE to market, surely they (and other mfgs whose hybrids predate start-stop) didn't just throw away all of that knowledge to haphazardly "bolt on" a start-stop system. They didn't, which is why start-stop equipped card have things like low-friction coatings on their crankshaft bearings. > The prius style dual motor/generator planetary gear arangment avoids concerns about starter motor longevity Redesigned starter motors with improved longevity also avoid these concerns. In start-stop systems, the starter motor is a safety critical item and they are engineered to a much higher standard. As far as I can find, there's only one start-stop starter related recall in the US (Honda) and it wasn't even a mechanical issue. > From my experience with a couple rental cars a year, on user experience, start-stop is all over the map from really annoying to noticable but unobtrusive ... I imagine how design challenges around lubrication are met is also all over the map. I think this captures exactly why people fixate on these systems. They assume that because they can be janky to use (they often can be), that they must be jankily designed. I can't prove a negative, but I just haven't ever seen meaningful evidence that start-stop cars fail faster or fail in the ways critics suggest they should. Surely we would see some evidence of the extra spun bearings, sparkly oil, and premature starter replacements that this almost 20 year old tech has has wrought by now, right? The only evidence I've seen are slightly more expensive batteries needing to be replaced slightly more often.