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As I know, clutch pressing and neutral gear both disengage the engine from wheels. So will it matter if I do not press the clutch if I start in neutral?

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    Someone once said to me that depressing the clutch rather than relying on neutral reduces the wear on the starter motor, as there is less drag due to the gearbox being disengaged completely. But I find it hard to believe that the difference would be anything but negligible. – Mark Henderson Nov 27 '16 at 18:03
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    @MarkHenderson I think he was right saying this. In the video link at 1:52 I can see when the clutch is not depressed and the vehicle is at neutral gear, all the parts of the gearbox except main shaft are engaged to the engine. But, when the clutch is depressed (at 1:10), the whole gearbox is disengaged from the engine. Evidently, the second option produces less drag. – Dwiparna Datta Nov 27 '16 at 20:32
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    @MarkHenderson For 100HP main engine, the difference definitely is negligible, but for 1HP starter motor it can be significant. – Agent_L Nov 28 '16 at 9:35
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    @MarkHenderson And if not a noticably increased wear, it will definitely increase its power consumption. With a weak battery, this can indeed be noticable. – Angew Nov 28 '16 at 9:45
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    @Angew good point. You just reminded me of a car I had with a terrible battery that would turn over, but not start with the car in neutral, but would start with the clutch depressed. It was a heavy clutch on a big, heavy gearbox on that car too. – Mark Henderson Nov 29 '16 at 20:46

11 Answers 11

38

It depends on the specific vehicle. Many modern standard transmission cars in the US have a clutch pedal sensor that will not allow you to start the vehicle if the pedal isn't fully depressed. You'll turn the key and nothing will happen.

I've had older vehicles that preceded this sensor that could move the vehicle if the clutch was engaged and the transmission in gear. This was cited as an emergency way to move the vehicle (e.g., if you stall on railroad tracks).

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    @R.. - the rare case when that might be useful seems to be outweighed by the liability if you (or someone else unfamiliar with your car), accidentally tries to start the car in gear and it rolls out into traffic or into a pedestrian. In nearly 40 years of driving I've never had the need to roll the car with the starter (not even when I drove a car that allowed that). Though I've seen friends accidentally try to start the car while in gear. – Johnny Nov 28 '16 at 4:03
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    @Johnny: Never had an ignition problem or failed fuel pump? It's really annoying not to be able to move your vehicle in such a situation, especially when you know it's an artificial limitation. With the starter you can move it to an appropriate place to make repairs, to avoid blocking other vehicles to your garage/driveway, or for easy access to towing. I had one vehicle that fairly regularly had electrical ignition problems and would use the starter to get it to the next suitable spot to stop on the shoulder and fix it. – R.. Nov 28 '16 at 4:21
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    Not just the US - here in the UK, new cars (especially performance cars) have the requirement to depress the clutch to start - almost certainly that safety feature: so the car doesn't jump forward if started in gear! – Rory Alsop Nov 28 '16 at 12:33
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    @R.. I would never endorse disabling safety devices to provide marginal assistance in corner cases like this. Better to solve the real problem. – Bob Cross Nov 28 '16 at 13:21
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    If it makes anyone think twice about disabling this - my wifes first car didn't have this. On her second drive she put it into a lamp post (and would of ran over her brother if he hadn't jumped out of the way) because of this. -- Yes she had a bad instructor who allowed her to learn to do this (leaving it in gear) but the point stands. – djsmiley2k Nov 28 '16 at 13:40
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Being from Canada, I feel compelled to mention that if you do not depress the clutch while starting when it is at all cold out (let's say < 0 Celsius) you will notice the starter motor labouring significantly as it spins both the cold engine and the cold transmission. If it is really cold, your battery may not have enough power to start the car at all in this situation.

This makes sense if you have ever tried to pour cold transmission oil; it is quite a bit more viscous than motor oil, and acts about like honey in cold temperatures.

This would be less of an issue when it is warm out, or if you are using synthetic transmission oil, but still is unnecessary wear on your starter and not a good habit.

  • I find it hard to believe it's noticeable. It would just be the input shaft bearings adding to the inertia. – Nick Nov 29 '16 at 19:56
  • As another Canadian who has owned a car equipped with a manual transmission and no clutch safety switch, I can attest to a noticeable difference between cranking a cold engine clutch in and clutch out. Not much, but noticeable. Same car (with carburetor) would exhibit a subtle drop in idle RPM while dragging the input shaft or slight increase when the clutch pedal was depressed. Actually, in a synchro transmission, the engine is spinning a lot more than just the input shaft even when in neutral. – Anthony X Nov 30 '16 at 3:55
  • @Nick All of the gears on both the input and output shaft are turning at engine speed when the clutch is out & the transmission is in neutral, just that the output shaft gears are not coupled to the shaft, so the car doesn't move. It is more noticable in a larger vehicle like a truck with big gears and lotsa oil -- I've even heard tell that under extremely cold conditions, there can be enough friction on the bearings from the gear oil to move the vehicle in neutral. I haven't seen this myself though -- I put the clutch in when I'm starting the car... :-) – jkf Nov 30 '16 at 5:33
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I drive an old landrover with a 202" straight six. And I was taught to start in neutral with the clutch out. This means the starter has to spin more mass, but that mass will help the engine turn over the top (pistons at either end of their throw)

To be honest it doesn't seem to make a difference either way in my experience.

However - Starting with the clutch underwater should be done in neutral. I can feel the plates sliding and the friction point becomes a guess. If your 4WD has stalled then its totally best to start with the gearbox in neutral and the clutch out, to keep the clutch plates drier, which may be necessary for exiting up out of the water. This one comes from personal experience.

5

In my opinion, this is a good practice to adopt. Pressing the clutch means that you disconnect the engine from the gearbox. Consequently, the power needed from the starter motor will be less. This will not only result to less wear out of the starter, but also requires less current from the battery (for cases where the battery condition is degraded).

In cases when the weather is cold, the gearbox oil gets thicker and the battery efficiency is reduced, this practice can save a lot of energy during engine start.

Now for the practical part: There will be times when the car will be -accidentally left- in gear (other than neutral). Pressing the clutch at start-up will prevent the car from moving (which at times can result even to a small collision).

So, the short answer to this question is a "definite yes"!

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    Having driven a manual for over ten years, I never -accidentally- left it in gear: I did it on purpose. – user4896 Nov 28 '16 at 15:35
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    Having driven manual all my life (I am 49), and I can ensure you that it just may happen... Not that it will, but may!!! In any case, starting with clutch depressed is a good practice -even for the other reasons that I mentioned :) – captain theo Nov 28 '16 at 23:50
2

In some cars (see Bob Cross reply) you really need to press the clutch pedal otherwise a sensor will prevent the car from starting.

But you should press the clutch pedal in most situations.

Reasons to press the clutch pedal:

  • You avoid the car "jolt and halt" in case you left a gear engaged. This mistake may cause mechanical damage or to bump against another car (or a wall).
  • Engine self-starter needs to move more gears, it's going to wear out sooner and to stress battery more.
  • The self-starter is going to need more battery energy to move the various mechanics that stay connected if clutch pedal is up. This shows a lot of effect when the battery is old, partly discharged or your car has been sitting in the cold for some hours.
  • Less powerful engines tend to come with less powerful self starters. Starting them is more difficult if you leave the clutch pedal up.

  • Old, strained, badly setup (carburation etc.) engines and very cold engines get difficult to keep running during the first 30 seconds - 1 minute if clutch pedal is up. Old cars with less than perfect lubrication or gears and ball bearings slight mis-aligment audibly feel the difference between holding the pedal up or down, the RPM audibly changes too.

Only reason I have found to start an engine with engaged clutch and gear is to take your car to repair when the clutch pump(s) or wire (old cars) break or get stuck. Some good car drivers manage to switch gears with a broken clutch but in general you are better to try and take the car to a nearby repair ASAP (in case you can't get it taken by a tow truck).

2

I'd be surprised if any mass production car sold today (in the US?) didn't have a clutch interlock. You have to press the clutch pedal to the floor to trigger a sensor to allow the starter to engage.

So to answer your question, if you don't have an interlock and are in neutral, it won't technically matter. Practically, however...

Pros:

  • You will save some wear on your engine's thrust bearing. But we're talking negligible even in the long term with most cars. Trouble with this is relegated to older vehicles with sub-par thrust bearings.

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Cons:

  • You might jerk the car forward/backward and run into people/things.

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To me the cons outweight the pros.

  • I have never owned a car with an interlock to prevent it being started without the clutch pedal depressed (plenty of bikes like that though). OK, tend not to have new cars, but my current car is a mk3 MX5. Are such interlocks really that common on manual cars? – Kickstart Nov 30 '16 at 11:08
  • @Kickstart, it might be a US thing, I've never come across it in Europe – Separatrix Nov 30 '16 at 11:45
  • @Separatrix - entirely possible, although also possible something that has become popular / compulsory in the last couple of years – Kickstart Nov 30 '16 at 11:55
  • @Kickstart - Interesting. My 1977 Datsun 280Z doesn't have one. My 2014 WRX has one. And so did the many manual cars I had or have driven before that. 1991 Nissan Sentra, 1992 Nissan 300ZX, various 90s and early 2000s cars (Ford Ranger, Ford Focus, etc.). It may be just a US thing. – Nick Nov 30 '16 at 18:04
  • @Nick - You might be right on being a US thing. Last few manual cars we have had are a 2006 and 2007 MX5, 2004 BMW 318, 2002 Jaguar X Type and 1999 Alfa 156 and none had such an interlock. – Kickstart Dec 1 '16 at 9:08
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There are two points which could cause your car to move if you start the engine: the clutch failing to disengage when you step on the pedal and the transmission failing to come out of gear when the lever is moved into a neutral position. Disengaging the clutch is a hedge against transmission failure and putting the transmission in neutral is a hedge against clutch failure. The chances of both failing at the same time are very small, so doing both considerably reduces the odds of having the car move unexpectedly.

This is even important on cars that have interlock switches because the switches may indicate that everything is in a safe state even if the actual mechanical state of a failed clutch or transmission is different.

1

One Possible issue with pressing the clutch while cranking the engine is that some of the load on the clutch is transferred to the crank on most engines. On a small number of cars this side load on the crank before there is any oil pressure can cause early failure.

Quite rare though (only one I have heard of it happening on quite often was the old 3.2L V8 Maserati engine).

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I always do that when starting and turning off the engine. It will prevent the car moving unexpectedly (if you forgot the car was actually in gear and not in neutral. Another thing worth consideration, mostly for modern diesel cars (but also modern, turbo charged petrol cars) fitted with Duel Mass Flywheel, is that pressing the clutch while starting the engine reduces the pressure on the wheel which should make it last longer. This is particularly important, taking into account the cost of replacing a DMF.

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    Yeah, but if it's still in gear from last time and you don't bother to check that it's in neutral before starting it with the clutch pedal depressed, once the car is started and you take your foot off the clutch pedal, it's still going to jump forward, but this time it will stall the engine too. – user12176 Nov 28 '16 at 21:01
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"Manual transmission" is in the question's tags: for such transmissions, you don't need to press the clutch pedal, if you are about to start the car in neutral. With manual transmissions you "always" should start you car in neutral!

Pressing the clutch pedal while cranking is possible, but it will add more extra wear to the clutch system, more load to the crankshaft and bearing since oil isn't pumping yet. As a rule: pedals (any of them) should be pressed when utterly necessary :) Keep your feet out of them as much as possible, except for gassing obviously. Press clutch, press break ONLY as needed.

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In the United Kingdom, doing so will normally result in you failing your driving test. :-)

In a vehicle without automatic transmission, if you switch on the ignition the vehicle WILL move if it has accidentally been left in gear. It will lurch forwards - or backwards - violently, without warning, potentially causing injury to pedestrians and/or damage to adjacent vehicles.

And if you have not depressed the clutch, you normally cannot tell whether the vehicle's gearbox has been left in neutral or is actually in gear. Bear in mind that manual transmissions, unlike automatics, do not have any visible label indicating the position of the transmission - there is no label marked 'park' - so how can you tell that the transmission is in neutral?

Sometimes the handbrake will hold a vehicle stationary long enough for the engine to stall, if you are lucky. But if the handbrake is off or faulty, and the vehicle is in gear, the vehicle will move.

In the UK, there are various criminal offences you can commit in this situation, depending on how unlucky you are, including driving without due care and attention, dangerous driving, and causing death by careless or dangerous driving.

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    This is just wrong. See gov.uk/guidance/… 1.29 - "The candidate should ensure that the handbrake is applied and the gear lever/selector is in neutral before starting the engine." (and that hasn't procedure hasn't changed in the last 40 or 50 years). it is perfectly simple to check that a manual transmission car is in neutral, by moving the gear lever from side to side in the "gate". – alephzero Nov 27 '16 at 18:36
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    @alephzero one may put a stopped car in gear on purpose and then forget this when starting the car. Leaving a car in gear may serve as an additional safeguard in case the handbrake fails. – IMil Nov 27 '16 at 23:51
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    Not buying any of this. It's pretty obvious touching the shift lever whether the transmission is in gear or not... – R.. Nov 28 '16 at 2:36
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    @alephzero "no good reason ever" - what about of the law requires you to? Like in San Francisco when parking at a grade of more than 3% - sfmta.com/getting-around/parking/how-park-legally – Erwin Bolwidt Nov 28 '16 at 7:16
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    I'd think that anyone who'd ever driven a manual would know that it's trivially easy to tell if it's in gear or not. I've developed a reflex of pushing the stick back and forth to ensure it's out of gear before I crank the ignition, even with the clutch depressed. – Rob K Nov 28 '16 at 18:56

protected by Pᴀᴜʟsᴛᴇʀ2 Nov 29 '16 at 21:17

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