I heard this from a local radio station... They said if you don't warm up your car first and just drive off, you'll be burning twice a much fuel than you would warming it up. I thought that was pretty intresting convo... I'm not a mechanic, so I can't really say if it's true or not... so... is it? Just wondering... you know being that gas prices are high and all


Modified by 13oz. at 10:22 PM 10/13/2005

 

Intresting, i want to know too :-)

 

not twice as much but u will burn more fuel if teh car isnt warmed up properly.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">
OBD 1 hondas don't have heated 02 sensors, so it takes longer for the ecu to reach closed loop. obd II vehicles do have four wire o2 sensors, less time.
Hope it helped out</TD></TR></TABLE>false... your info is just wrong. my OBD1 gsr has a four wire o2 sensor.

 

Twice as much, not quite. Goldenstreets got it though

 

warm up time for a honda is less than a few minutes, you will burn all that extra gas whether you sit there are drive for those few minutes. In moast areas you are gonna do better to just drive gently the first few minutes and pur that warm up rich phase to work moving your car rather than wasting it sitting around waiting for the car to warm up.

By the way thinking about it, my wideband o2 sensor controller shows the warm up process of the heater circuit in that sensor and it is usually less than 1 minute until its warm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">my OBD I Civic HB has single wire. And so do alot of people I know with say 92-95 civics, accords, etc.</TD></TR></TABLE>

That's because you have a CX. The majority of Hondas and Acuras had 4 wire O2 sensors from 92 and up.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">During cold start up, injector pulse time can be inbetween 20 to 80 milliseconds</TD></TR></TABLE>

Um, your car would flood. My wideband records AR ratios of ~13:1 when the car is cold. You're saying that the ecu injects 10 times as much fuel when the car is cold? Sorry, I don't think so. In addition, you would reach 100% duty cycle at idle, around 725 rpm. And considering the fact that the ecu can't even work with fuel values that high, I don't see where you're getting your info.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Boostage &raquo;</TD></TR><TR><TD CLASS="quote">not twice as much but u will burn more fuel if teh car isnt warmed up properly.</TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">Okay, I don't want to be "just wrong" and offend anyone, so how's about this. I'll generalize my statement. A four wire heated o2 sensor wasn't mandatory for auto makers to have standard on new vehicles until OBD II, which wasn't put into place until '96, give or take a few months.
So big ups to Honda for instituting it earlier, which Honda is known for meeting future standards early. But, my OBD I Civic HB has single wire. And so do alot of people I know with say 92-95 civics, accords, etc.

Next, at normal operating temps, injector pulse time is inbetween 2 to 8 milliseconds. During cold start up, injector pulse time can be inbetween 20 to 80 milliseconds. Now, that may not seem like a huge difference because it's all in milliseconds, but if you think about it; your ecu is programmed to dump more fuel, added to that the fuel your dumping into it by driving away.
Let's not forget about the engine. On a cold startup, and then immediately drive away, the entire engine hasn't gotten a fresh splash of circulating oil. So your wearing parts, as well as wasting gas.
So to the on topic initial question, yes by driving away without giving your car ample time to warm up, your wasting gas, def. not twice as much, but until your car hits closed loop(which means until the o2 sensor reaches 600 degrees F,
your using unecessary fuel, and slowly as it may be, wearing away engine parts.
just my 2 cents, hope it helped out.


Modified by goldenstreets at 4:56 PM 10/14/2005</TD></TR></TABLE>



You're talking out of your ***, that is all.

 

ROTFL !

I love HT....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote">

That's because you have a CX. The majority of Hondas and Acuras had 4 wire O2 sensors from 92 and up.

Um, your car would flood. My wideband records AR ratios of ~13:1 when the car is cold. You're saying that the ecu injects 10 times as much fuel when the car is cold? Sorry, I don't think so. In addition, you would reach 100% duty cycle at idle, around 725 rpm. And considering the fact that the ecu can't even work with fuel values that high, I don't see where you're getting your info.</TD></TR></TABLE>

actually he is correct your car would not flood when the car is cold the compression is close to a point higher when the car is cold than hot. without the extra fuel you would be running the car lean at cold start. not to mention the idle speed is 1500 rpm as opposed to 750

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BADEG4 &raquo;</TD></TR><TR><TD CLASS="quote">

actually he is correct your car would not flood when the car is cold the compression is close to a point higher when the car is cold than hot. without the extra fuel you would be running the car lean at cold start. not to mention the idle speed is 1500 rpm as opposed to 750</TD></TR></TABLE>

How is it possible a cold engine has MORE compression ?

I ask because when the internals are cold, the clearances would looser ... Which would mean you'd lose compression...no ?

 

well can you warm up your car by revin it up....? it takes forever for my clusteer temp to go up...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">it's gonna take the 02 sensor more than just acouple minutes to reach 600 degrees</TD></TR></TABLE>

Catalytic converter lightoff times are around 30 seconds in most Hondas, and there's a lot more mass in a catalytic convertor to heat up than in the O2 sensor. Combined with the heater, the O2 sensor is up to temperature in a manner of seconds, not minutes. You can't compare heating a gallon of water on the other side of an aluminum wall to heating a tiny zirconium plate directly in the exhaust stream, which can exceed 1400 degrees.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">Actually as metal is heated it expands, so when it cools down it contracts, making the clearances tighter, and that is why BADEG4 is correct in saying that compression is higher on cold startup.</TD></TR></TABLE>

Ok, then ponder these points:

1. Does all metal expand and contract at the same rate? If it doesn't, then maybe some metals expand at a higher rate, causing certain clearances to close up.

2. When a compression test is performed, is it done on a hot or cold motor? If done on a hot motor, are the results higher or lower than a cold motor, and why?

Oh, and I found this, sort of sums everything up:

http://www.ama.ab.ca/advocacy/Vehicle_Idling.pdf

 

Damn... I sure could learn a lot from this site... It's HT from now on, thanx e'rbody...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 13oz. &raquo;</TD></TR><TR><TD CLASS="quote">Damn... I sure could learn a lot from this site... It's HT from now on, thanx e'rbody... </TD></TR></TABLE>

Just remember: take everything with a grain of salt. Just because someone said it doesn't mean it's true. That goes for everything, no matter how knowledgable the person sounds. Don't believe what I say because I said it, use it to find more knowledge and ask more questions. You'll see people say things and have thoughts of your own, and the best thing to do is follow those, that way you have an understanding, not just a collection of facts.

&lt;/rant against people who spout BS&gt;

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">The original question was basically asking that if I don't let the car warm up in the morning will I be burning more fuel.</TD></TR></TABLE>

I agree with this. And it makes me wonder what the hell the rest of your post has to do with it. Did you read the link I posted at all? It appears to be broken now, try this: http://64.233.161.104/search?q...hl=en

Most of the rest of your post is explaining how heated o2 sensors reach operating temperature quicker, and how a cold car has more emmisions than a warm car. No one is arguing this! Like you said, the question is if you will consume more fuel by idling until the car is warm, or driving it until it is warm. Either way it's going to warm up, the question is which is more efficient.

The article outlines how it is more efficient to warm up the car by driving, as noted here: "Compared with idling, driving a vehicle reduces the warm up time by half. This issignificant from an emissions standpoint, because during the warm-up period, the engine and emission systems are not operating at peak efficiency." So if someone actually wanted to answer the original question, that is something they could say.

Like I noted earlier, my wideband O2 sensor(which reaches operating temperature in 30 seconds) shows an AF ratio of around 13:1 when the car is cold. While this is richer than the stoichiometric ratio of 14.7:1, it is still less rich than experienced under moderate acceleration getting on the highway, or getting in the gas hard to have some fun, on a stock ecu tune anyway.

And if you do the math on it, it requires more air to drive the car than it does to idle it. It therefore requires more fuel to mix with that air. The more fuel you consume, the more BTUs of heat you are releasing, therefore heating the engine and coolant faster than you would just sitting there with air just trickling through the FITV.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote">1. Does all metal expand and contract at the same rate? If it doesn't, then maybe some metals expand at a higher rate, causing certain clearances to close up.

2. When a compression test is performed, is it done on a hot or cold motor? If done on a hot motor, are the results higher or lower than a cold motor, and why?</TD></TR></TABLE>

And I never got an answer to those questions. Just trying to keep people honest, is all.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">


Actually as metal is heated it expands, so when it cools down it contracts, making the clearances tighter, and that is why BADEG4 is correct in saying that compression is higher on cold startup.</TD></TR></TABLE>

I don't think that is correct... when the metal cools, it contracts, the clearances would not get tighter when the engine cools down, the clearances would get looser.

 

That's really most of it, I see misinformation and I think of how many people will read it and take it to be truth, and it just causes problems. I'm not trying to prove anything, because it doesn't work over the internet, that's for stupid people. I'm just stating what I know and what is fact. Nothing I say is meant to be a personal attack in anyway.

The question was:

So it's not a matter of emmisions or anything like that, it's a question of which one uses less fuel.

I (respecfully) disagree with you on that note. You had stated previously that "If you pull away in the morning without letting your car warm up, and don't have the car in closed loop mode, where the ecu is reading from all the input sensors, and making fuel trim adjustments based off of those readings, you'll be burning more gas. " The article directly contradicts this when it states that "Idling is not an effective way to warm up avehicle, even in cold weather. The best way to do this is to drive the vehicle."

Not according to the overwhelming evedence to the contrary. I searched for warm up engine on google, and found an awful number of sites, some from very knowledgable people, saying that it's better to drive off and use the load to warm up the engine than it is to sit and idle with no load, which takes a much longer time to bring the car up to operating temperatures.

Ask yourself, what percentage of the cooling of the engine is performed by air passing over the outer surface of it? Is it 50%? 20%? 10%? Maybe less? As water cooled engines, these cars do not experience any significant cooling from ambient air on the block itself, in fact, aluminum has pretty crappy heat transfer characteristics. There is some cooling due to the air passing over the engine, no one can argue that. But one can say that the rate of heating due to increased compustion under load greatly outweighs the rate of cooling due to the air passing over the engine. Warmup times are increased by an insignificant, though certainly measurable amount.

You must again ask yourself a question: what is the alternative for the race driver who wants to get the car up to operating temperature before getting out on track and having to drive at high rpm? He can't just go haul the mail around the paddock, he has to be in grid waiting to go on track. And since the car must be warm so as not to damage things due to cold oil, etc, he has no choice but to idle. Fun fact: Busch cars with a dry sump oil system must be plugged into a 120v outlet for ~20 minutes to heat the oil prior to starting them.

Sorry this got so long over a simple question.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by X2BOARD &raquo;</TD></TR><TR><TD CLASS="quote">I don't think that is correct... when the metal cools, it contracts, the clearances would not get tighter when the engine cools down, the clearances would get looser. </TD></TR></TABLE>

Ding, you win the prize.

 

whether you pull away or not you will run rish during warm up. driving the car will warm it up even faster leading to faster light off of the cat, and whether you drive or sit makes NO difference to the o2 sensor warming up.

 

Remember though, through out the whole time your car is sitting there idling, it's using fuel and running rich as well. The question is: does idling use more fuel than driving to warm up the car. Let's consider it logically. We can say that once the car reaches operating temperature, it uses the same amount of fuel no matter what method was used to reach that temperature. It might be reasonable to let that temperature equal 180 degrees, and we could say we start both methods at 80 degrees. So now we have to determine which method uses less volume of fuel to reach the predetermined temperature. We can say that each method of warming up will use fuel at a different rate, but over a different amount of time. Like speed and time equate to distance travelled, the rate of fuel delivery and the time equate to volume of fuel used. So it's a matter of comparing the rate of fuel delivery and time required to reach the operating temperature of both methods. Let's say that the car takes 10 minutes to reach 180 degrees idling, and 2 minutes of driving to reach the same temperature. So the question is, does driving require 4 times as much fuel as idling?

And also consider that the entire time one car is sitting there idling, the other car is driving towards the destination. If you want to calculate miles per gallon during the warmup, the car that is driving might be getting 20 miles per gallon, but the car that is idling is getting ZERO miles per gallon.

All the talk about which car has greater emissions has nothing to do with the question. The fact that the cat has not lit off has nothing to do with the amount of fuel consumed, and the O2 sensor will obviously come up to operating temperature longer under driving than idling.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">You said that "since the car must be warm so as not to damage things due to cold oil"- so can't we apply that also to what we are talking about with our daily driven cars that get us to and fro from our lively hoods,</TD></TR></TABLE>

Any why not? Aren't the same engines used in racing as the street? My friend's Spec Miata engine is no different than my other friends daily driver miata, and Honda Challenge cars are bone stock as well. Engines are engines, and rely on the same physical principles no matter what environment they're in.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">And just to clarify; i'm all about our cars. Love Hondas. Have no personal feelings against anyone who posts on here; in any case, unless they make it personal. I think that drdisco69 has put in thought and time to his perspective and if everyone puts in this kind of effort into their posts, then I believe this site would be much improved with it's purpose to educate people about our cars, which would cause the readers to be more informative sources for others.</TD></TR></TABLE>

Thanks for the complement, like I said before, I just speaks the truth. And Honda 4 life. Some people say different, but Honda are some of the easiest cars to work on, and anyone who thinks otherwise is into s&m.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goldenstreets &raquo;</TD></TR><TR><TD CLASS="quote">P.S.-Even though that last paragraph was touchy feely, warming up the car at idle is still more efficient for overal fuel conservation!!!! </TD></TR></TABLE>

Gloves are off, this means war!

 

o2 sensor heats up in 30 seconds.
cat lights off in 30 seconds.
engine coolant and oil heat up in longer than 5 minutes while idling, less than 2 while putting a load on engine.

the only time those might change is during sub zero temperatures.

Most competent mechanics will tell you to warm up for 1-2 minutes up north, like Minnessota winters, but furhter south you would be wasting gas and causing more pollution than needed.

 

You speak of wasted fuel and excessive unburned fuel. Once again, sitting still and burning fuel seems like an extremely inefficient use of fuel to me. And the use of 20 mpg was an example to illustrate the fact that the engine running with the car not moving nets 0 mpg.

As I noted before, it's obvious that starting the car and driving away runs the engine rich, and that there is excess fuel being delivered. But my point is that the time in which the engine runs rich is less when a load is applied and heat is created to bring it up to operating temperatures. You know that the harder you drive a car, the hotter the engine gets, as the more energy is being released from burning the fuel. So it would be reasonable to say that any load you can put on an engine would help it reach operating temperature faster, and the less time it spends enriching the fuel mixture.

Another thing to consider is just because the O2 sensor has reached operating temperature doesn't mean the car immediately starts running at 14.7:1 AF ratio. The coolant temperature sensor compensates for cold coolant by adding fuel, so the sooner we can heat the coolant, the quicker the engine will get to the stoichiomentric AF ratio. The only way to do that faster is to add more load to the engine to release more energy from the fuel. While more fuel is added due to the cold start condition, it is added over less time, and the net result is less fuel is used.

You have undoubtably noticed that engines run at a higher rpm when they are cold. One reason is that the fuel does not atomize very well when the engine is cold, so it cannot idle as well as when it is warm. The other reason is to get more heat into the engine quicker, reducing warmup times. That is the key, reducing the amount of time it takes to warm up the car. The more load you can put on an engine, the faster it will heat up, and by driving towards your destination, you will already have covered distance that the car idling has to drive while it has sat burning fuel and now has to drive over.

The EPA knows a thing or two about fuel economy, and they say "Letting your car idle to warm-up doesn't help your fuel economy, it actually uses more fuel and creates more pollution." See http://www.fueleconomy.gov/feg/factors.shtml

In all my searching, I haven't found a single bit of evedence that states that idling the engine to warm it up is more efficient than starting it, waiting a few seconds for the oil to circulate, and driving away. I have found countless pages that state the contrary, that the load on the engine reduces the cold start time and decreases fuel consumption and emissions. If you have a source for where you're getting your information, I would be more than happy to see it.

 

Rather than base my behaviors on theory that may or may not be true (I don't have a clue) I'm in the process of attacking this problem with real-world data. Since I bought my car in July I've been in the habit of just turning the key and going. I've kept the revs low and load light until the engine gets to temp but I've been moving nonetheless. Overall mileage had been steady at 31.5mpg. As soon as the weather got cold I started seeing my combined mileage go down below 30, with my last tank at 29.7mpg in a 50/50 city/highway mix. (Mileage actually follows the curve of average daily temp for each interval...the trend is quite clear.) For the next couple of tanks I've decided to see what happens when I allow the car to warm up every single time. This means pulling away once the temp needle has swept up past the first mark and into the normal region. It took inside of 2 minutes this morning with 50F ambient air temp. Once I have good data I'll generate plots for all to see. If anobody else wants to do something similar it would make things more interesting than having data from just my one car under my particular conditions.