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-   -   Idling Time during Morning Start for MPFI Vehicles (https://www.team-bhp.com/forum/technical-stuff/11161-idling-time-during-morning-start-mpfi-vehicles.html)

I've heard some people saying that there is no need for running the vehicle at idle speed for the first start of the day in the case of MPFI engines. Is it true ?

But I've heard in the opposite way that every vehicle needs to reach the optimum working temperature especially for the first-run of the day for the best performance.

OR for much time should the vehicle be idled before taking off ? Is 40 seconds enough ?

please:

MPFI cars do not require idling.


don't rev it hard first thing in the morning
and idling was required for carb cars not for MPFI ones

MPFI cars do not require to be idled for long periods during cold start to reach operating temperature - however.....

if you notice, when you first start your MPFI car after leaving it off over night or a couple of hours, the engine always revs at a higher speed for a short while. during this time, your engine management system pumps in extra fuel into the engine to help it reach optimum operating specifications. after a minute or less, the revs drop down to regular idling speed.

a good time to start driving is when the high revs have dropped to regular idling revs. ofcourse, allow the engine fluids to begin flowing before you start revving hard or you're bound to damage the moving parts.

you can begin driving before the revs settle down but the motion will be jerky as the engine management system conflicts with inputs from the accelerator.

waiting for the revs to settle down also provides enough time for the oil to do its work in lubricating the movie parts.

in very cold temperatures (around and below freezing) its always recommended to let the car warm up for a short period before moving off. this is because as the external temperature drops the engine fluids become more viscous and hence, do not do their lubricating job effectively. driving off immediately in very cold climates will automatically cause your car to jerk & stall - this Very Bad for your car!!!! lots of friction between moving parts...

It would be better if u let ur car idle for arnd a minute before rolling and using the AC. Also keep the car below 2500rpm for a little time till the engine warms up. And again while stopping, a minute of idling would again help. This is just in general, not just MPFI

Hi Mithun,

I would suggest letting the car idle for a MINIMUM of 15-20secs ALL THE TIME before starting to drive. This gives the oil a chance to make its way around the engine and lubricate all the moving parts before you start to put load on the engine by driving.

In particularly cold conditions, idle for a longer time. (The colder it is, the longer you should let it idle).

Once you have waited past the 20secs for the oil circulation, any longer you wait just gives the engine time to warm up to "operating temperature". As you know, metal contracts a very tiny bit when cold, and expands when heated. This changes the clearances of moving parts inside the engine.
So waiting another 20secs to a minute is ideal if possible, and if you want to treat your car with the most care possible.

cya
R

in practical life that temprature variation is so small that change in physical measurment of metallic parts doesn't even come into play

Are you saying that difference between cold/resting temperature and operating temperature of pistons, piston rings, cylinder sleeves etc is "a small temperature variation" ?

And also given the fact that these parts are made with such high tolerance means that they are more sensitive even to tiny changes in dimension.

cya
R

You have a point there, but the variation in physical dimension is almost negligible.

Manufacturers test their engines at working temprature. (& various other tests too)
So if metal contracts as you say it, if it will reduce in size only, posing no extra friction. (it should be less than normal friction offered)

cheers
aditya

PS: we are totally offtopic so lets debate over it in PM, & for now lets return to topic

Makes the transmission on my car sound really whiny first thing when I start it in the morning. Takes a few minutes of driving to heat er' up ! Viscous transmission fluids.

yes, MPFI cars donot require idling for long durations.

but for some decent lubrication of moving parts, it is better to keep it idle (after a stopover of about 6-8 hours) for sometime, say about 25-30 seconds.
no need to adopt to this practice for lesser stopovers.
even after idling for 25-30 seconds, try keeping car in low revs and donot gather much speed for a km or so. after those initial glitches you can fire it up, if you assumes that as a glitch! it'll soon become a habit which shall not intrude much into your everyday rushness!

Also, never start AC until engine reaches some warm temperature. starting AC instantly after sitting in car even before moving puts a great load on engine and cabin takes really long time to cool up.

MPFI cars do not require Idling because they adust the RPM according to the engine requirements.

start the car ...and then settle down ...i.e adjust the mirrors ,the seat belts ,hands free and the like ....alll this will take a minute .....by this time the engine will have reached the operating temperature ...

when i start the car in the mornings the rpm is usually 1500 rpm ....i wait for it to come down to 800rpm before i start moving .....this takes 2 mins at the most ....also doing this will help the oil to circulate .....as teh maximum wear n tear happens during cold start when there is less oil to lubricate the moving engine parts

In Delhi .. mornings get a bit chilly..... so if one waits for it to get down to 800rpm .. it'd take about 5 mins.
I just wait for it to start showing signs of revving down, that normally takes 1-2mins. I believe that is a must.

Also i don't drive it hard or switch on the A/c till it completely warms up.

CR@P!!

Do u mean it won't let u rev beyond 3000rpm if engine's cold??

Nitrous - Please disagree in a polite manner!

And even though i disagree with his point, he did not say anything about the ECU letting you revv beyond a certain limit when cold. (Although cars like the E46 M3 have a revvlimit that changes as the car warms up)

I think what he means is that on carb cars, if the car is not warmed up enough, the engine will stall occasionally (in cold conditions) if you just let it idle (if the idle speed screw is set at a low enough setting), but in MPFI cars that doesnt happen since the ECU keeps it idling higher till it warms up.

Devarshi, read the thread and see why we say idling is important before you dismiss it by saying its not neccessary on MPFI cars.

cya
R