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.
Caveat: For cars not equipped with automatic start/stop, the starter and possibly the battery might not be specced for it so it could cause additional wear. Cars with start/stop systems often assist the process with precise camshaft position measurements and the ability to squirt fuel pretty much right away so the starter doesn’t need to do as much work.
Also don’t do it with a cold engine - it’s better to get the oil up to temp faster, it’ll also reduce fuel consumption as the engine heats up.
Thanks for reminding everyone of this. The gas savings over time will probably end up being the same, or less, than a starter on an older vehicle. Of course, if you’re not planning on keeping the vehicle until it dies, this is less of an issue for you.
It’s the battery prematurely dying that’s also an issue. Especially if the battery needs coding to the car. Could be a £300+ job. That’s a lot of fuel that’d need to be saved to be close to worth it.
It’s all about emission testing anyway. Keel start stop off.
It’s amazing how much batteries have increased in price since Covid.
I bought a car battery for my GF while I was out and she was upset at how much money I spent until she went online and saw that $200 for a car battery was totally normal.
If memory serves me right, it wasn’t long ago that many were well below $100.
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Stop start cars have more expensive agm batteries typically
I saw Matt needed a lithium battery for his M5. £750. Yes it’s a big and technology rich battery but wow.
Last I saw my M240 battery was about £200. Bet it’s £350 now.
Assuming it’s the battery shortage due to electric vehicles.
Wait, CODING? Are you serious? I can understand this with EVs, but for a standard 12 volt battery? This sounds more like a thing they do to keep you from doing your own work and allowing shops to charge more flag time for what should be a 10 minute job. Replacing a dead battery is one of the simplest jobs you can do. The hardest part of a battery swap should be finding your 10mm socket.
Yeh, you have to tell the car a new battery is installed to alter the V for start/stop mainly.
This is such absolute crap. The math didn’t check out in the slightest, and the backslapping on this topic alone could Flintstone a vehicle all by itself. 🤦🏼♂️
I always wondered why hybrids could start their engines instantaneously, when many conventional cars couldn’t. This is why, isn’t it?
I can’t speak for other cars, but my Prius uses the electric assist motor as the starter motor as well. Compared to a regular ICE car that’s a massively stronger electric motor than average starting a smaller than average engine.
My favorite thing about it though is I have the longer hatchback model and if you replace one of the back seats you can fully lie down for car camping. What about the heat you may ask? I can just leave the AC on overnight, the car will start up and use the engine like a generator to recharge the battery then turn back off autonomously. I always keep some spare gas in case but I’m always shocked how little it uses.
According to priuschat you can leave your prius “idling” with light duty power draws (a small lcd tv and a fan) for about 7 days on a full tank of gas.
Also I think on the prius the starter motor-generator is also the one that bleeds excess engine power to charge the battery, but I’m not 100% sure on that one.
Regular old cars use weak starter motors from the 12V battery. They’ve gotten better, but it’s still just a small part used only to start the car, so it only turns over the engine fast enough to get it going.
A car like a Prius will put the car’s big, beefy generator in “reverse” to start the motor at whatever RPM the computer wants it at, and since it has abundant power from the synergy drive batteries, it can start the engine at whatever RPM the computer deems appropriate.
Also the fact that a hybrid has a huge electric motor to start the petrol engine instead of a small starter motor.
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I still find it kind of unsettling, to be honest!
When it’s cold it can be beneficial to let the car idle for about 15 seconds before moving, to get the oils moving. They don’t usually need much more than that, unless it’s very cold of course.
Also cars will warm up faster driving around minimizing wear while engine is cold. Just don’t stomp on the gas go easy on it
Indeed! It’s a balancing act. It’s good to wait a while right at start, but then it’s better to go than wait on idle.
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There are no hard rules, cars are different and so are oils, but I personally would give it a few minutes under 0F and maybe up to a minute if it’s just a bit under the freezing point, but not too cold.
Of course, something like a 0w30 oil will get pumped around the engine much faster in the cold than a 10w30 or 10w40 and therefore won’t need as much time.
Also, idling isn’t terribly good for your engine either, you should only do it enough to get the oil flowing and the blower to start putting out a tiny bit of warmth. Then you’re better off driving, because that warms up the engine faster.
Everything I’ve read says that newer engines (like last decade or two) only need a couple seconds. All the warming up for a minute plus advice was literally from carburator-era engines. Newer engines will be damaged from running cold far more than anything else, so it’s best to give them a second or two and then drive to get them warmed faster. That DOESN’T mean to push the engine or red line it, but easy driving.
But I’m not a mechanic, just a super type-A scientist that looks into things at a semi-ridiculous level for the sheer joy of knowledge.
The few seconds is bare minimum, but you can improve on it. Again, if you live in a warm climate, this doesn’t apply. I give my engine a maximum of 5 seconds of idle time in the summer too, because I know the oil isn’t too viscous at those temperatures and I don’t need to demist my windshield. But in the winter, you can tell from the sound the engine’s making that it’s not happy at -30C, even in a fairly new car with good oil. So you start off idling a bit and then start driving gently. I let it idle till I can see the mist starting to disappear from the windshield on its own, then drive real gentle - luckily I usually drive on low-traffic roads in the morning, so I don’t have to gun it to the speed limit in one second to keep everyone else happy.
There is truth to the damage from excessive cold idling, which is why I don’t recommend doing it too much on newer cars either - in direct injection cars in particular, I believe you can wash oil film off the cylinder walls with excess cold idling. But a minute or two is fine. We’re talking about temperatures that people from warmer climates might consider deadly cold. Not just mildly freezing temperatures
Right. When I wrote my comment I just took -15C winter temps as normal. That’s cold. 0C is a warm day half of the year.
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Sounds completely reasonable to me. 5w20 is pretty thin, which is good for winter driving. Again, don’t idle too much, but a little bit is good.
Yeah, I wouldn’t recommend long idling*, but I also wouldn’t recommend shutting down the engine for short stops when it’s cold. Just keep it running if you’re stopping for less than 5 minutes.
* Where I live, the winters can get to around -30C, though normally it won’t get colder than -25. You’ll want to let your car idle for a few minutes because otherwise it’s not going to be blowing any warm air at the windshield, and your visibility will be shit.
Yeah. When you’re down into those temps you’ve got to keep your car starting in a multitude of different ways if it stays outside anyway. But generally, just starting and rolling out instantly could cause wear. I’d not really say it’s anything to be worried about though.