# Cold engine = less power



## MCHNHED (Dec 22, 2002)

Just a general question, why do cold engines have less power?


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## captain_shrapnel (Sep 10, 2004)

I might get flamed if this answer isn't right, but I think the engine gets a rich fuel mixture to help it idle until it warms up. Like choking a carb.


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## chimmike (Oct 17, 2002)

if you're trying to run a cold engine hard, it can damage it. this is why they always suggest you let the engine warm up to normal operating temps.

cold engines haven't let the metals expand from the heat and in turn run as designed.

I imagine you're applying the "colder intake air=more power" to "cold engine should=more power" but it's not correct.


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## pete? (Jul 6, 2004)

chimmike said:


> if you're trying to run a cold engine hard, it can damage it. this is why they always suggest you let the engine warm up to normal operating temps.
> 
> cold engines haven't let the metals expand from the heat and in turn run as designed.
> 
> I imagine you're applying the "colder intake air=more power" to "cold engine should=more power" but it's not correct.


he didn't say anything about making more power when the engine ran colder, all he was asking is why they make less while cooler, mike you have to chill out you get pretty snappy. the reason he may be asking this is because everyone has seen the additives for the radiator that say it will reduce your engine temp 30 degrees. also everyone has heard that an engines worst enemy is heat and it robs the motor of hp. while this is true the engine has be designed (like mike has already said :cheers: ) to work at a certain temp.


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## xbrandonx (Mar 27, 2004)

1.6pete said:


> he didn't say anything about making more power when the engine ran colder, all he was asking is why they make less while cooler, mike you have to chill out you get pretty snappy. the reason he may be asking this is because everyone has seen the additives for the radiator that say it will reduce your engine temp 30 degrees. also everyone has heard that an engines worst enemy is heat and it robs the motor of hp. while this is true the engine has be designed (like mike has already said :cheers: ) to work at a certain temp.


I think he was just clearing that up. As far as reducing the engine temp 30 degrees I don't see that as a problem, then engine will still be warm, the engine will have had its chance to warm up get set to be ran. However you wouldn't want to go outside right now and try to drag your car as soon as you turn it on (its about 35-40 degrees here right now) 

However you don't want to too hot, of course...if you do just drain all your fluids and you can get it warmed up in no time :thumbup: 

The colder air is denser, that also allows more air to be sucked in from a CAI.


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## Token Moron (Mar 28, 2003)

im pretty sure hes asking why when u first turn on a motor, it seems slower/less power than once the motor warms up to operating temp. captain shrapnel is "kinda" right about it...but thats not the only reason in which it seems slower.


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## chimmike (Oct 17, 2002)

1.6pete said:


> mike you have to chill out you get pretty snappy.



you need to back the f*ck up and chill. I didn't do anything to you, and even if I did, I had my own reasons and it can't be changed. 

So, get over it, and stop talking about it.


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## MCHNHED (Dec 22, 2002)

cHoPs said:


> im pretty sure hes asking why when u first turn on a motor, it seems slower/less power than once the motor warms up to operating temp. captain shrapnel is "kinda" right about it...but thats not the only reason in which it seems slower.


you, sir cHoPs, are the only one who understood what i was asking, but, you are also the only one who did not provide an answer! how ironic


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## pete? (Jul 6, 2004)

MCHNHED said:


> you, sir cHoPs, are the only one who understood what i was asking, but, you are also the only one who did not provide an answer! how ironic


Actually Mike was all over it. When things are cold everything is tighter (cold=shrinkage you should know that :thumbup: ) so there is more friction effectively robing your engines power. When it heats up it expands and things loosen up and friction reduces allowing your motor to move much more freely :cheers:


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## Token Moron (Mar 28, 2003)

actually, captain shrapnel is right, when the motor is cold, the sensors arent up to normal operating temperature. so when this happens, the motor dumps, and i mean dumps fuel to compensate for this.. making the motor run rich which in turn makes it feel as if the motor is running like shit.


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## jetsam (Feb 7, 2004)

MCHNHED said:


> Just a general question, why do cold engines have less power?


Thermal efficiency is decreased as more energy is lost from combustion to the engine. In part, this is why modern thermostats don't open until 220 fahrenheits.


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## MCHNHED (Dec 22, 2002)

1.6pete said:


> Actually Mike was all over it. When things are cold everything is tighter (cold=shrinkage you should know that :thumbup: ) so there is more friction effectively robing your engines power. When it heats up it expands and things loosen up and friction reduces allowing your motor to move much more freely :cheers:


to me, it would seem more intuitive to say that friction would INCREASE when the engine parts expand, no?


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## pete? (Jul 6, 2004)

MCHNHED said:


> to me, it would seem more intuitive to say that friction would INCREASE when the engine parts expand, no?


there is alot of metal to heat up in an engine block, and the time that it has not expanded yet things are tight and cramped. im sure that it is from runing lean but this may have something to do with it as well


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## himbo (Sep 20, 2003)

well theres a couple reasons why the engine creates more power in colder conditions
1) for ever 10 degrees dropped, the engine gains roughly 1% more hp
2) cold air (in general, not the intake) is more dense, and creates a fuller combustion
3) if i'm not mistaken, on the some cars, the timing is advanced to create bc the car is a little less prone to knocking, so cars simillar to the GA16's gain a little more power.

of course, this is up to a certain point, its about 40 deg here in Jersey, and my car is running like a champ, and its bone stock!!!


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## pete? (Jul 6, 2004)

accualy he was asking why it makes LESS power before it has reached normal operating temp. not why a cai creates more power than just a wai............ :cheers:


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## himbo (Sep 20, 2003)

oh... ok, well then, thats because the metals of the engine have not expanded to their full size, and because the oil is (for a lack of better terms) gooier, and a little less fluid
but i wasnt talking about the intakes, but the intake charge rather :thumbup:


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## Nissan200sxSER (Dec 20, 2002)

The engine makes more power when it is cold. IT MIGHT NOT RUN AS SMOOTHLY but it will make more power. This is why drag racers will open there hoods inbetween runs to let there car cool down (not cool down completely, but somewhere inbetween operating temp and Cold). The law of thermaldynamics proves this but i dont remember it enough to tell you why it proves it. 

However taking the car up to redline when the engine is cold is not safe as was mentioned before.


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## himbo (Sep 20, 2003)

1).dragster engines are not built like street engines, and, 2). they cool them down after a hard run, which causes EXTREME HEAT


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## Nissan200sxSER (Dec 20, 2002)

himbo said:


> 1).dragster engines are not built like street engines, and, 2). they cool them down after a hard run, which causes EXTREME HEAT



I was actually refering to any engine (completely dragged out or stock, it doesnt matter). 

The only times ive been to the track has been for the street legals, and i can tell you that most people will turn their car off and push it while waiting in line and they will pop there hood to let the engine cool down.

The maximum efficiency (the power) of a heat engine depends on the difference between the hot and cool sources of the engine. The combustion gases are obviously going to be the hot source, and the engine block,head,manifold,etc are going to be the cold sources. The hot source will spontaniously flow to the cold and heat engines use this energy to do work. The larger the difference in hot/cold, the more the "hot source" will flow to the "cold source". When more "hot flows to cold", greater amount of work is done.


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## WhiteFox (Sep 4, 2002)

*^^^^^^^^^^^^^^^^^^^^^^^*

:jawdrop: Anybody know where to start on this doozy?


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## himbo (Sep 20, 2003)

Nissan200sxSER said:


> I was actually refering to any engine (completely dragged out or stock, it doesnt matter).
> 
> The only times ive been to the track has been for the street legals, and i can tell you that most people will turn their car off and push it while waiting in line and they will pop there hood to let the engine cool down.
> 
> The maximum efficiency (the power) of a heat engine depends on the difference between the hot and cool sources of the engine. The combustion gases are obviously going to be the hot source, and the engine block,head,manifold,etc are going to be the cold sources. The hot source will spontaniously flow to the cold and heat engines use this energy to do work. The larger the difference in hot/cold, the more the "hot source" will flow to the "cold source". When more "hot flows to cold", greater amount of work is done.



when they cool their engines, they are cooling them back to their operating temps


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## Token Moron (Mar 28, 2003)

lol......wow


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## pete? (Jul 6, 2004)

normal cars don't run at the rev limiter almost the entire time............hence they stay at normal operating temps (were they make the most power, thats the reason the thermostat is set to that temp) drag cars/race cars pop there hood or have cool down laps after a race because they are running so hot some times that if they simply shut the engine off they would seize............not good (wouldn't make any power :thumbup: ) the saying "heat is the engines #1 enemy" isn't all that great, in this case "excessive heat is an engines #1 enemy" works much better


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## himbo (Sep 20, 2003)

1.6pete said:


> normal cars don't run at the rev limiter almost the entire time............hence they stay at normal operating temps (were they make the most power, thats the reason the thermostat is set to that temp) drag cars/race cars pop there hood or have cool down laps after a race because they are running so hot some times that if they simply shut the engine off they would seize............not good (wouldn't make any power :thumbup: ) the saying "heat is the engines #1 enemy" isn't all that great, in this case "excessive heat is an engines #1 enemy" works much better



Good call pete :thumbup: 
for an engine to produce optimal power, it generally has to be at operating temp (not to be confusded w/ what the manufacturer set it at). again, thats why race engines have to be cooled down to their operating temp.


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## MCHNHED (Dec 22, 2002)

WOW... i'm relieved that at least SOME of you know what you're talking about. Even though no one has really answered my original question in full, i think i'll just force myself to be content with the current state... especially after hearing what Mr. Nissan200sxSER had to say. wow...


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## pete? (Jul 6, 2004)

lol i completly forget what your origonal question even is...........hell i forgot i posted in this thread until it poped up in my user cp lol


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## himbo (Sep 20, 2003)

What_ is_ the original question????  :wtf:


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## pete? (Jul 6, 2004)

original question said:


> Just a general question, why do cold engines have less power?


we soooooooooo answerd that


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## bowtie420 (Dec 25, 2004)

Fuel Atomizes better at higher temperatures.

Fuel delivery is not controlled by coolant temperature, but air inlet temp has an effect. IT is delivered on % of engine load, manifold air pressure (MAP) or Mass Air Flow (MAF), Throttle angle and all that jazz (OBDII) The PCM reciveves the inputs and monitors the air fuel ratio, always trying to find its ideal, usually 14.7:1 (stochiometic) 

Race engines run at a lot hotter temperatures than your grocery getter runs. They are always run to an extreme, therefore they need to be cool to protect their investment. True, cold air has a better effect on performance, but usally cold air intakes really dont suck cold air unless routed properly. Air intake temps can rise from a CAI, due to its ability to suck in more of that hot air from engine operation.
idk, my 2 cents, a small intro to temp and effect.

Also, an engine needs to get to a certain temperature before it will allow these inputs. (OPEN LOOP) The computer controls everything, the metals and expansion and shit doesnt really mean shit. You measure engine clearances when its cold.........true expansion occurs but restriction, please, ever actually build an engine, they arent very resticted metal to metalwise. thats why you have oil in it too..............


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## MCHNHED (Dec 22, 2002)

bowtie420 said:


> Fuel Atomizes better at higher temperatures.
> 
> Fuel delivery is not controlled by coolant temperature, but air inlet temp has an effect. IT is delivered on % of engine load, manifold air pressure (MAP) or Mass Air Flow (MAF), Throttle angle and all that jazz (OBDII) The PCM reciveves the inputs and monitors the air fuel ratio, always trying to find its ideal, usually 14.7:1 (stochiometic)
> 
> ...



THANK YOU. so might you say that less power at start up is mostly caused by the fuel/air ratio being non-stoichiometric?


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## Twiz (Aug 24, 2004)

Yesterday I drove about 45 miles on the expressway. I couldn't get past 80 mph, I floored the gas pedal and nothing, rarely it'd come close to 90 mph. The engine temp gauge was under normal cause of speed and outside temperature and I had a CAI installed. (the car reached normal temp in the city traffic but then it went down while driving at high speed) When I drove back home I took the CAI extension tube out and I moved the filter behind the battery. The engine temp gauge was still under but the car was accelerating fast like the usual past 80 mph. I was thinking of installing a shield in front of the radiator... just when it's really really cold outside.


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## Zen31ZR (Mar 24, 2004)

Twiz said:


> Yesterday I drove about 45 miles on the expressway. I couldn't get past 80 mph, I floored the gas pedal and nothing, rarely it'd come close to 90 mph. The engine temp gauge was under normal cause of speed and outside temperature and I had a CAI installed. (the car reached normal temp in the city traffic but then it went down while driving at high speed) When I drove back home I took the CAI extension tube out and I moved the filter behind the battery. The engine temp gauge was still under but the car was accelerating fast like the usual past 80 mph. I was thinking of installing a shield in front of the radiator... just when it's really really cold outside.


You lost power because the engine wasn't as warm as the ECU though it should be and so was still in the warm-up cycle. For no other reason, really. Do you have the correct thermostat installed in this car. Doesn't sound like it....... The correct thermostat will cycle and keep the engine at a constant temperature, not let it rise and fall like that, no matter how cold it is outside.


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## Twiz (Aug 24, 2004)

The car has 110K miles and that's the original thermostat that came with the car... I don't want to run with the engine cold or under that adds a lot of wear to the engine. So you're saying the cold air intake has nothing to do with this ? I never got a CEL with this car, I'm guessing the ECU will set a code if the temp sensor doesn't make it to the normal temp.


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## Zen31ZR (Mar 24, 2004)

Twiz said:


> The car has 110K miles and that's the original thermostat that came with the car... I don't want to run with the engine cold or under that adds a lot of wear to the engine. So you're saying the cold air intake has nothing to do with this ? I never got a CEL with this car, I'm guessing the ECU will set a code if the temp sensor doesn't make it to the normal temp.


 I doubt the CAI has anything to do with it, yes. I've run external filter mountings (Under bumper, behind headlight etc) on various of my other cars, and it's never affected internal engine temperature to any degree. You gotta figure by the time the air hits the combustion chamber, no matter how cold it is ambient, it should have hit at least 100 degrees or more. If it wasn't above a certain temperature, you can bet it would crack red hot exhaust valves. 
No, your problem lies with the thermostat, and since this is what the ECU consideres a "Soft" fault, it will never set a CEL. All the ECU thinks is that the car is just not finished with the warm up cycle and will not go into closed loop mode. If this were one of the newer gen OBD-2 systems, where the ECU determines if the length of time to warm up is too long, then yes it would set a CEL, but yours , being older, will not.


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## Twiz (Aug 24, 2004)

I agree... it seems logic the thermostat would be the only factor. I will pull it out of the cooling system and test it before I get another installed. (It's prolly stuck half open) Thank you! :thumbup:


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## spdracerUT (Jun 11, 2002)

two reasons: cars generally run overly rich while in the warm-up phase. the other reason is a colder motor/coolant means colder cylinder walls which extracts heat the air/fuel during combustion. Heat being extracted means heat that isn't going into increasing the temp/pressure of the air which means less force pushing the piston down.


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## Joel (Jun 11, 2003)

jetsam said:


> Thermal efficiency is decreased as more energy is lost from combustion to the engine. In part, this is why modern thermostats don't open until 220 fahrenheits.


This is definately a contributing factor.


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