YSK: A car takes uses about seven seconds worth of fuel to start up. If you are going to idle for a period of time longer than that, you'll save fuel by turning your engine off.
YSK: A car takes uses about seven seconds worth of fuel to start up. If you are going to idle for a period of time longer than that, you'll save fuel by turning your engine off.
Why YSK: People seem to, on average, think that a car takes a lot of fuel to start up. In reality, it takes on the order of a few millilitres of fuel to start an engine. That means if your car isn't equipped with an automatic start/stop system to stop your engine instead of idling, it saves fuel to turn off your engine and start it back up when you need it.
Caveat: air conditioning and radio might not work with the engine turned off.
Scenarios where this might be useful include waiting for trains to pass at rail crossings, waiting for food at drive-throughs, dropping off or picking people up on the side of the road when they need to load stuff, etc. May not be a good idea to use this while waiting at a red light because starting the engine does take time which would annoy drivers behind you when the light turns green.
Some cars are equipped with systems that will automatically stop the engine when you are idling for a while (e.g. waiting for a red light). If yours is, then manually turning off your engine will probably result in reduced fuel savings compared to just relying on the car to do it for you.
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Starting the engine puts as much wear on it as driving for 50 miles. Automatic start/stop hurts engine longevity by doing that unnecessarily and should always be turned off.
My car uses 0.5l of fuel idling for an hour. There's no way in hell that a start/stop system would even save 10$ a year, so there's no benefit to using it.
That's not true, cold starts cause wear not warm starts.
At most it's starter motor and battery wear, start stop cars have agm batteries for that reason.
What about the fact that the oil drains to the pan in those few seconds that the engine is stopped?
This is my real concern. Sure you can upgrade starter motors and batteries to handle the extra cycles, but you can’t do anything about increased scoring and wear on cylinders in the milliseconds before the fluids start to circulate again.
Some start stop engines have auxiliary oil pumps. I don't know much about them besides random research I have done in the past out of curiosity.
Napa also claims some vehicles have auxiliary water and transmission pumps as well.
That might be true, I’m not a mechanical engineer but despite that, my understanding is that within the engine block itself, cylinders are primarily lubricated via the system holding pressure. This pressure starts to drop the second the engine ceases.
You can notice the effect on cars that have realtime oil temp monitors. Mine does, and it’s digital. My stable oil temp is around 216 degrees Fahrenheit. After a start-stop cycle, even for only 5-10 seconds or so, the temp drops about 5-8 degrees. After a minute, the temp is down 25 degrees. That’s significant. Essentially the engine is no longer “at temp” for the first 30 seconds or so after it resumes. That’s 30 seconds of additional semi-cold, under pressure wear each cycle.
Then why do so many new car models have auto-stop features that kick in at red lights? They would not do that if it wasn't more efficient.
Well I think I can answer that. It is more efficient for fuel consumption. They all have the systems because it allows them to hit better EPA fuel economy numbers. But better fuel consumption doesn’t mean there’s no effect on the engine.
I’m not saying I’m 100% correct btw, I’m waiting for a mechanical engineer to explain why I’m wrong. But my limited understanding hasn’t found an answer for my concerns yet.
My Ram start-stop automatically starts the engine back up once temps drop to a certain point for this exact reason.
Auto stop-start has had many years of advancements to work out these issues.
That’s makes sense but from an engineering standpoint, anything below operating temp and pressure fundamentally causes more wear.
It may be minimised with configurations such as you describe, but it’s still more wear than if the engine hadn’t stopped in the first place.
How much, I don’t know, but over the course of hundreds of thousands of miles and thousands of stop-start cycles, it adds up.
Cold starts cause more wear than warm starts, but a warm start still causes a lot of wear because the engine doesn't have oil pressure when it's off, so it doesn't have good lubrication until it turned over a few times.
Besides that, my car and many others will happily stop the engine on their own even before reaching operating temperature. At least I can turn it off with a single button instead of going through a menu on a touch screen.
Hmm while its true it wont have oil pressure, for the short time its stopped there would still be oil on the bigend bearing to crankshaft interface and on the cylinder walls, and oil pressure will be restored quickly before going above idle as the oil pump is primed.
And a heavier duty starter that is specifically made to be used often.
Believe it or not, they thought of that when they created start/stop systems.
In cars with these systems, the back pressure in the engine's cylinders is greatly reduced via a variety of strategies including selective alteration of valve timing and purpose-built secondary valves. What this means in effect is that the torque required to re-start the engine is a fraction of a dead cold start, and even a fraction of a normal warm start. This should serve to minimize additional destructive wear on components.
In effect, well-designed start-stop systems do not create any additional wear on vital engine components versus the engine running for that same period of time.
The difference in wear might be too small to measure, but what we can measure is how much fuel it saves. And that's usually less than 50l over the lifespan of a vehicle. Those systems don't even offset their own cost unless you spend all day at railroad crossings.
They are there for two reasons: Getting better results in unrealistic tests and decreasing the amount of control that owners have over their vehicles.