Emilaman

hi, peoople.
i want to ask question which is my main bet with my friends.

some mechanics says that you dont need to warm up engine before drivin, others says that if you want your car work long you need to ckange oil regularly and warm up engine.

i do it everytime. but my friends dont agree with me.

VVT-i

I just let the car idle for about 5-10 seconds after cold start(GA winters weather is about 18-40 degree overnight) and drive normally,no racing or anything. I think oil company want you to warm up the engine for about 10 minutes so you will buy more gas...

jcastaneda

iTrader: (5)

I know in Germany they have a law that you can't let your car warm up in the morning. I think as long as you don't decide to tickle the floor with the right pedal you'll be fine.

aprince1

iTrader: (5)

Warming it up is not as necessary as it is to wait for the oil to circulate the engine before you put the car in drive and speed off.
Also the first couple hundred feet you should refrain from revving the engine to above 2000 rpm too.

mitsuguy

iTrader: (2)

as has been mentioned... warming up on a conventional engine is not necessary anymore... the concerns are that the oil pressure has come up and that you are not beating it up until it has got some warmth in it...

as a cars engine heats up, tolerances between the pistons and the cylinder walls change - depending upon the composition of the alloy in the piston, there will either be larger tolerances or smaller tolerances as the engine warms up... most engines have very tight tolerances when cold and as it warms up, the tolerances open up a little - the oil thins and flows better once warm as well... by revving high when all of this is still cold will not allow oil to completely do its job and the tight tolerances can lead to excessive wear...

all of this being said, you want the most power out of most engines, you want to literally start the car, let oil pressure come up, and then full throttle right away - because of the tighter tolerances cold and air temperatures as well, you will get more power from the engine...

sc-driver

iTrader: (7)

Not necessarily, when you first start up a car, the car will run in something called open loop mode. This means that the "brain" of the car isn't getting any signals from the oxygen sensors. So essentially, the car is "guessing" on how to run based on rpm, throttle position, speed, air temp....To be on the safe side, ecu's always run richer ==> hence more "power".

Once the car warms up and reaches closed loop, it starts reading signals from the oxygen sensors and runs at it's best efficiency.

Emilaman

so the same bet starting again=)) Its like circle.

Emilaman

Im looking for car like its alive, so its hard to wake up human at morning and ask him to do something, cuz he needs time to realize whats going on.

Jetfire

iTrader: (3)

don't idle. just start your car up and put it in gear. if it's really that cold out, get a block heater.

just keep the revs low. under 2k until your car warms up.

Emilaman

okay, one thing. i noticed it on every car.

When starting the cold engine RPM going like till 2k but after like 3 minutes RPM going down and you even can hear how engine kinda calms down. What is that?

oguitar

That is the way modern ECU's get the car warmed up quicker.

mitsuguy

iTrader: (2)

Sorry, was talking about my drag racing days with custom ECU's and even no ECU's...

The car never guesses, in open loop mode, it goes off a pre-programmed map... there is something similar here, though, as at wide open throttle, it also goes to a pre-programmed map as well (most cars)... Up until recently cars have not come with wideband O2 sensors from the factory... anything less than a wideband sensor and you aren't getting proper air fuel ratios by going based on the O2 sensor output... Ya see your normal 1 volt O2 sensor is only really accurate right at stoichiometric, 14.7:1 air fuel ratio... You give most cars that kind of a/f ratio at full throttle and they will knock and run great, for a short amount of time, long enough to burn them up...

so, if you are saying that a car makes more power in open loop mode, I'll agree, they are programmed to go into open loop once they reach a certain throttle percentage or load... if you are saying that cars don't make more power when they are cold, well, I can absolutely guarantee they do... the bigger the turbo, the bigger the aftercooler, the placement of the air intake box, the size and composition of the pistons can all attribute to an engine making more power when cold vs. warm...

ever watched people stage cars at the track? do you think they push the car all the way up to the burnout box for a reason?

mitsuguy

iTrader: (2)

specifically O2 sensors and catalytic converters - its an emissions thing...

mitsuguy

iTrader: (2)

runs at its best fuel efficiency...

not its most power... its most power is in open loop, read off a pre-programmed map...

when we program a computer, we program them at what spot to change over from closed loop to open loop and how much a computer can change its maps based on O2 sensor information during closed loop operation...

sc-driver

iTrader: (7)

^^I think there seems to be a bit of confusion going on. By "guessing", I mean that the car doesn't know what the output is. I completely agree that maximum power is met during open loop mode just as in the case when the car goes into open loop mode when you step hard on the throttle. Fuel Feedback in this case is ineffective.

What I was arguing was that it is not necessarily true that the added power you feel during a cold start is "because of the tighter tolerances". Shrink fits work in the complete opposite way. They are loose when cold and get extremely tight when warm. The rate of expansion is based primarily on the type of metal.

Also, since the ecu is in open loop, there is no output "check" (no 02 sensor feedback loop). Then the ecu runs a map that has a slightly richer air to fuel ratio and this is the added power you "feel".

Most ecu's strive for a 14.7 afr and slightly higher afr's give you more power....up to a point

So I think the confusion was that I was thinking about stock cars, and you were probably thinking drag racing Also the cold I was referring to was internals, not air temperature.