Car question

---

Is it better to turn off your car then restart it or let it idle if you are only going to be out of it for about a minute or two.I do this alot with my job and just wanted to know the best way not to waste gas, cause I go through alot of gas.

That's a good question. Since starting the engine takes a significant amount of energy from the battery, which makes the engine work harder replacing it, there must be some length of time for which it's better to keep the engine running.I suspect, though, that unless your car is really hard to start, even warm, that time may be very short, probably well under a minute. If you're going to be out of it for a minute, I think it's probably better to turn the engine off. Besides, if you're going to be actually out of the car, having the engine running is a bit of an invitation to thieves.I remember people used to say it was better to leave fluorescent lights on because they take more energy starting, but it turns out to be very rarely true.

which makes the engine work harder replacing it, You think? Once the engine is running the alternator is supplying voltage whether the battery is run down or not.

Yes, but the current flowing is less, because a fully-charged battery has a higher voltage.

You can leave a florescent light bulb turned on for 28.2 seconds before you start wasting more energy than turning it off and on.As for cars, I've no idea about power consumption, but by leaving it idle you are wasting gas and releasing unnecessary pollutants into the air. Not to mention that leaving your car unlocked, with the keys inside and the engine running is just asking for it to be stolen!Some States have created little by-laws stopping people from leaving their car idling, like in Massachusetts it is illegal to idle your vehicle for more than 5 minutes (except for certain conditions, which does not include warming your car up in winter).

Hello Hotpants,It depends. How long has the car been driven before you shut it off for that brief amount of time? If it's not had sufficient time to warm up before shutting it down the first time, you'll waste more gas the second time because each start requires more air/gas to enter the intake manifold and engine as that's what heats the engine. Ever notice on a cold day you first start a car the RPM's jump way up there and then settle once things are moderately warmed up? Also, in terms of life of engine, start-up is when the most damage occurs because no fluids have been flowing through the parts and lubricating the bottom end of the engine: Crankshaft, bearings, rotating assembly, etc. You're better off leaving it running for the brief second or minutes you're going to be out of the car. Honestly the amount of gas wasted when not under load is not that much. You'll waste more gas at a stop light.

True, but the current flow doen't detract from the engine. The engine runs no matter what. More current from the alternator does not place a load on the engine. If you turn on the air conditioning, then the compressor loads the engine. The alternator however rus freely based on engine speed, independent of the current flow.

But the alternator loads the engine more, depending on the power it produces (which is of course the product of its voltage and current). The power has to come from somewhere. It used to be easy to demonstrate this with the old bicycle dynamos.

Generators have maximum rated amperage, but if you have nothing connected to them, no current flows (except to the field coils, which is only a small amount).

Actually that's not the case. The regulator determines how much power the alternator produces by controlling the current fed to the rotor windings. In a low demand situation, the alternator will produce less power; with greater demand it produces more power. Also, the voltage is not constant. It can vary from around 13 to almost 16 volts depending on conditions

Holy shit

why holy shit?

Crazy discussion going on here. HOw many people are following this conversation besides those involved?

I know...But it is interesting to hear what guys, mostly, will say about car conversations.You guys know your cars, or at least try to pretend you do, not necessarily talking about you guys in this thread, just car talk in general. lolAfter reading some of the things in here, I feel like we need someone to go to the chalk board and show us a diagram... lolThanks for the comments though.With my job, I do sometimes get out and in it my car alot and I do leave it on most of the time, cause that is what I thought would not waste the most gas. I thought it took more gas to start it very time.

I understand what you're getting at but the alternator is free spinning. Say you have no current flowing and the alternator is spinnig at a given RPM... With a large current flow, the alt. is still going to spin at the same RPM. The engine (running on gas) does not strain to accomodate the extra current flow. If the current exceeds the capability of the system, then the voltage drops to compensate.. That's why if your battery dies (from a shorted cell), you have a hard time running the engine becasue the battery short drops the voltage to the point where the system can't produce a spark.

Test #6 Avoid Excessive IdlingResult: More important than we assumed Cold Hard Facts: Avoiding excessive idling can save up to 19 percentRecommendation: Stopping longer than a minute? Shut 'er down.If you turn off a light bulb as you leave the room you'll save electricity. If you turn off your car you will save gas. Obviously. But related questions are more difficult to answer. If you're only stopping for only a minute, is it better to shut off the engine or keep it idling? Should I shut off the engine in traffic? How much gas will this save? What rule of thumb do I use when trying to save gas this way?Method: We took two cars and drove a 10-mile route stopping 10 times for two minutes. We shut down the car each time. Then we drove the same route at the same speed and let the car idle for two minutes. Save gas???

Thanks.

You're forgetting, sdp, that the alternator puts a load on the system. When there is no current the load is only friction, but when there is current it is more. When current is running through the alternator, it acts like a motor, generating torque in the opposite direction to its driven speed, which has to be overcome by the driving engine and in turn loads it. If it didn't, you'd be getting power for nothing.Helms, I think, is making a different assumption, that the alternator is always producing the same current. It's true that it does produce some current always. It runs the sparking and other electrics, and the voltage regulator takes some, and there is a little current through a fully-charged battery. However, current through a fully-charged battery is converting water into hydrogen and oxygen, and this is undesirable, so the voltage regulator is set to keep this at a minimum. (The voltage of a full-charged battery rises sharply and there's a fair over-voltage for gassing, so this is quite doable.) But when the battery is less than fully charged, the current increases to recharge it.

The UK highway code recommends 3 minutes to turn off ur engine. Problem is though it can at times be difficult to judge how long you are gonna be waiting for. Your best option is to swap to something more enviormentally friendly.Go Manual - Manual boxes are more efficient, you have full control of ur gears and can choose to sit in higher gears when you dont need the extra kick of a lower gear. I will often drive at 30mph in 6th although smaller engined cars may differ.Go Diesel - My understanding is that in the US diesel is still not a popular choice although modern diesel cars are massivly more efficient (2litre Diesel cars will give over 50mpg easy and have much more torque than petrol cars). I drive a 3litre V6 Ford Mondeo ST220, my dad has a Ford Mondeo 2litre TDCI Diesel and under normal driving conditions isnt much slower!A lot of new cars have auto cut out options too! Citreon cars will automatically cut the engine when in neutral with the brake pedal pressed and on release of the brake will automatically start up again.Ultimately you are only gonna muster a few mpg in your current car and it is cheaper in the mid-long term just to get something eles.Ps. DONT get the Prius, there seems to be a silly assumption that it hugs the enviroment, its only a tiny amount better than a similar sized petrol car. Diesel is cheaper and cars that run on it are as good as their petrol equivilents!The Vauxhall Corsa 1.3 Diesel only emmits 114g/km of CO2!

we own 2 Diesel trucks. they are made for traveling so unless ur on the road alot (and when i say on the road i mean hwy not in the city.) Diesels get better milage/diesel if you drive them a longer distance. the stopping and cutting them off a lot isn't good. i mean it’s not going to hurt them it’s just uses up more than it would if u let it keep running. we have a explorer to go into town with... it's smaller and it's gas. For driving to a fast food place or to pay bills diesels arn't a good choice. (lmao..and i am from the US...)