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Old 16th February 2007, 06:48   #1
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Question Engine switch-off procedure in cars

I am not able to find a thread on the above and hence posting it here.

Mods: Please do the needful if deemed necessary.

I have observed a lot of drivers (cars and other four wheelers too) rev up the engine a bit before turning the ignition off. I was given to understand that this practice was done to ensure that the battery was in good charge the next time the car was started and to make it start the engine with a single crank. Is this true ? Also, is this the correct procedure or are there any threats associated with this ? Tech gurus - your expert comments please !
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Old 16th February 2007, 08:57   #2
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Not sure, but I feel it is about lubricant circulatation for the engine parts for the next start.

btw, I have not noticed people doing this on new generation vehicles.
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Old 16th February 2007, 09:15   #3
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People mostly do this in diesel cars but it does damage the turbo i think cuz once u rev and turn off the engine, the engine will stop while the turbo continues spinning
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Old 16th February 2007, 09:31   #4
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I am one of those who rev before switching off, especially after a night's drive. it is more out of habit than for any useful purposes. i used to do that in my dad's old amby which suffered from serious battery discharges.
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Old 16th February 2007, 09:39   #5
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Well, I heard the other way. One should let the engine settle to idle before switching off! Any ideas?
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Old 16th February 2007, 11:08   #6
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with modern day alternator set up its not necessary to keep the engine running/reved after a regualr nights running unless the battery is weak or heavy usage of battery. even then keeping rpm at 1000 will give you max charging and then idle for say 10 secs and switch off.

it is otherwise not recommended to rev high before stoppin, rather idle for couple of secs and then switch off, specially true if the engine is a turbo

also reving out before stop wastes fuel
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Old 16th February 2007, 11:57   #7
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Yeah, I remember my driver telling me that, it's always good to rev up the engine (In terms of Diesel Amby) before shutting it off, so that the silencer rattling will be avoided. I am not sure if it really helps on a long run....

Cheers,
Jai
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Old 16th February 2007, 12:19   #8
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The M-800 carb model sometimes gives problems if you switch off the engine while the fan is running.

you need to let it idle and wait if the fan is running before switching it off. If you do switch it off while it is running. the car will have difficulty in starting the next time.

I noticed this in a few 800's.
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Old 16th February 2007, 12:52   #9
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Quote:
Originally Posted by nevertouchme View Post
so that the silencer rattling will be avoided.
This doesnt make sense.

Quote:
Originally Posted by vid6639 View Post
The M-800 carb model sometimes gives problems if you switch off the engine while the fan is running.
This point has been mentioned for the Tata vehicles too - to not switch off when the fan is running.
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Old 16th February 2007, 13:17   #10
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Quote:
Not sure, but I feel it is about lubricant circulatation for the engine parts for the next start.
For old turbo engines it was recommended to let engine idle for 1 minute before switching engine off. However in newer generation cars it is not required.
Eg. in old Scorpios it was mentioned that you should let engine idle for 1 minute before switching it off. But no such warning in CRDe.
This thread (Indica Turbo - Idle for one minute before shutting off?) might of more interest on same topic.

As for petrol cars I don't think there is any need to rev engine before switching it off.

Quote:
The M-800 carb model sometimes gives problems if you switch off the engine while the fan is running.
Quote:
This point has been mentioned for the Tata vehicles too - to not switch off when the fan is running.
Palio has good solution to this problem. Where fan keeps on running for needed interval even after you switch off engine.
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Old 16th February 2007, 14:04   #11
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FYI,
This procedure helps:
PETROL CARS: once you start or stop the car you need to run the car in idle for over 30 secs(not revving, they spoil your engine) in order to let the fuel burn the lean mixture of petrol residues on the valves.
TURBO DIESEL ENGINES: idling the vehicle before starting and swichting off has something do do with the turbo in the vehicle charge up to create certain amount of pressure(Revving is unnecessary).
quote me if i am wrong.
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Old 16th February 2007, 14:38   #12
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oh yeah fan coming on, yup keep the engine running at idle till it switches off so that the coolant temp and engine temp are brought down

m 800 carb (good observation) well thats basically due to engine coughing at shut off, specially true when engine is out of tune (point setting, point wear etc)

i often wondered why Palio fan thing operates, it will just kewl the radiator since flow will be minimal without water pump runnin ??? or is it as a safety feature to save the radiator from excess pressure due to boiling coolant ??

@ pavan
Petrol car ok
Turbo (Diesel or Petrol) helps in cooling the turbo internals and oil circulation, point discussed enough to death in the forum

Last edited by adya33 : 16th February 2007 at 15:19.
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Old 16th February 2007, 14:42   #13
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I read a sticker on the dashboard of a Scorpio, saying "Turbo charged engine. Run at idle for a minute after starting and before shutting off engine. "
Isn't a minute a looong time? Does anyone really do that?
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Old 16th February 2007, 15:53   #14
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Quote:
Originally Posted by prabuddhadg View Post
"Turbo charged engine. Run at idle for a minute after starting and before shutting off engine. "
Isn't a minute a looong time? Does anyone really do that?
I Do. Every time. .
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Old 16th February 2007, 16:01   #15
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Quote:
Originally Posted by condor View Post
I Do. Every time. .
That's great condor. And I was reading the sticker and thinking, "What humbug. Who does this for a whole minute.?"
You know what? My Petra has an injector light that comes on every time i turn the first click of the key. I am supposed to crank after the light goes out. The other day, I mistook the thir gear for the first and the car shut down on a crossing. Starting again, with people honking like crazy I cranked before the light went out. Now you have made me feel guilty.
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