QuestionWell, my 2006 Nissan Altima 2.5 hits 1400 rpm when it is just started and then quickly decends to 12 or 1300 rpm but for it to come down to 800 or less it takes maybe 4 minutes. I checked the 2002 Altima of a friend and it had the same reading and process. He said you drive off at 1200 rpm....but he bought his car in this country for the first time! Another has a Honda Accord and after kicking to 1500 when started it quickly settles at 1,000 rpm. It would take 4 to 5 minutes to settle at 300 rpm idle after the engine has warmed up.
So, to wait until it decends to 800 or less would be quite a waiting, dont you think?
Thanks Don. You've been great!
Sincerely
Greg
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Hi Don!
Following up on the question, how long should one wait before driving away, after the car starts up it settles at 1,300 rpm in the cold weather. After warming up fully its normal idle is 300 rpm. You mean to say, that I wait for 10 to 15 seconds on that 1,300 rpm and then am fine to drive away?
Thanks Don.
Greg
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In winter when you start the car the RPM shoots up to about 1,000 RPM and it takes time for the engine to level down at 300 RPM. Should one wait for the engine to warm up?
Is it safe to start and drive off? And if has to wait, wait for how long? Mine is a 2006 Nissan Altima 2.5.
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Good question!
It used to be in the days of the carburetor, that the "choke" set high idle and you could tap the throttle and drop rpm's almost immediately. In cold weather though, your engine would die as the cold manifold and carburetor caused the fuel to condense out of vapor.
Today, the choke is controlled by computer, and fuel injection insures better fuel spray into the cylinder, but cold starts still require higher rpm. Why?
Again, it comes down to the fuel not liking to say in vapor or mist in cold weather. think about your glass of tea in the summer. Water vapor in the air condenses on the side of the cold glass. In your engine in winter, the gas vapor condenses on the cold passages of the manifold and head/valves before getting to the combustion chamber. Big drops of fuel are harder to start burning and burn get to burn fully than a finer mist or vapor.
The choke function of modern cars artificially shuts off the air intake to the system and pumps more fuel into the injectors to make up for the loss of fuel along the cold metal path, and the bigger drops of the mist. This richer fuel mixture, along with a higher idle, also controlled by the computer, now keep the engine running for the first few seconds when things are warming up and combustion chambers heat up to burn fuel more efficiently.
In most cases, idle will drop to normal levels within a minute, but it is not necessary for you to sit in the car for a full minute.
A good rule is to start the car, and wait for the idle to drop at least partway. Usually this happens within 5-10 seconds at most. By this time, the oil pressure in the engine is up to full pressure, and the automatic transmission and power steering are also at full pressure and circulating well. (I am a believer in synthetic oil and tranny/power steering fluid as they flow better in cold weather and hold up to heat better in hot weather!)
If you try to get the car moving immediately upon startup, you are pushing things some, and it is best to wait a few seconds at least.
After 10-15 seconds, you usually can put the car in gear and drive away without it stalling or slamming into gear from being at too high an idle. A little high idle won't hurt.
It is not advised to sit and idle the car for a minute or more, you are wasting precious fuel. Also, your car will warm up quicker when driving, than just sitting at idle.
It is also advised, in cold weather to not push the car hard (hard acceleration, high rpms) for a few minutes after the first start of the day, or after the car has sat for several hours. Give it time to warm up and get fluids flowing, grease warmed up a little. Drive easily, and don't push for the first 5-10 minutes or the first 5 miles or so.
It can take half an hour or more for all parts of the car to come up to full operating temperature in cold weather.
In warm weather, you can cut that warm up time down some, but still give the car that 10 seconds or so at least to come off high idle some before trying to move out.
Don
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My answer below indicated that after 10-15 seconds, the typical modern car has usually come down off of high idle (typically 1200-1500 rpm) and is below 1000 rpm.
If your car is still at 1300 rpm after that time, then give it a little more time. You didn't say, but I would ask how long your car takes to come off of that first high idle, say to 800 or less?
Don
AnswerGreg, My 96 Taurus SHO drops below 1000 rpm easily within 15 seconds or so, and most cars/trucks I have had do so. But waiting 4-5 minutes for the car to drop is waiting too long in my opinion.
If our car (automatic transmission I assume?) doesn't slam or bang into gear after waiting 15-30 seconds, then I say go ahead and drive it.
If the transmission slams into gear hard, then something is wrong and you need to get it checked. I don't know of any car that recommends waiting 4-5 minutes upon every cold start before going into gear and driving. That wastes a lot of fuel, and is really not necessary.
Don
