Faster when engine is cold?

[msb71]

Been noticing this alot lately , when I don't let the truck totally warm up I notice it has a WHOLE lot more pep than when it is warmed up , is this normal or something else. I have a few ideas as to maybe why it is like that , I want to hear what others have to say.

Mike

 

[Skandocious]

Hahahaha Mike!!! I JUST noticed this 2 nights ago... I was gonna post about it but I didn't wanna get flamed. LOL!! I've noticed the exact same thing.

 

[Mr. Stroker]

Fuel is cooler maby?

 

[lil_dq]

could it be the cooler charged air in the engine bay till the area warms up?

 

[msb71]

Hahahaha Mike!!! I JUST noticed this 2 nights ago... I was gonna post about it but I didn't wanna get flamed. LOL!! I've noticed the exact same thing.

So I am not alone...the verdict is still out.

Mike

 

[NeXtras]

more so cold air than anything.. cold air is more dense so the engine will be a little peppier.. if the egine is really cold it will NOT be faster cause the oil is still thick and all the fluids are still warming up.

Something we know very well here in New England! lots of mornings in the teens. Its fun tho when the eingines up to temp and its reallly cold, you fly!!

Cold ENIGNE = Slower --- Cold AIR = faster

 

[eco]

From what I have been told, every 13 degrees cooler the air is that enters the motor you gain 1hp. But, it seems unlikely that this is the cause of the cold engine having more performance than the same engine at operating temp, especailly if the intake air is insulated from the underhood air. I would think more along the lines of the sensors that the computer begins to look at once operating temp is met.

 

[Skandocious]

Well why would the engine being cold mean the air coming in is cold...? If you've got a cold air intake like these trucks do from the factory, the temp of the air should be RELATIVELY constant, except for the fact that the underhood temp doesn't get a chance to heat it when its traveling through the intake duct. But I can't imagine that the underhood temp is going to affect the intake temp THAT much... This was a drastic change that I experienced. Rounded a corner and mashed the gas and the girl I had in the car got scared, lol. The tires screeched all the way around the turn.

 

[eco]

Skan, if the underhood temp is high, which it should be after the motor has been running for a while with the hood closed, the upper plenum will conduct that heat to a point as will the lower manifold and heat up the air inside it. Also, heat from the motor will conduct to the lower manifold. There isn't much that can be done about this since they are aluminum.

 

[Skandocious]

True, I didn't think about that... But the air is moving from outside to the combustion chamber in a matter of what, 1-2 seconds? And you say 13 degrees = 1 hp... My truck felt like it gained about 10-15 hp, the way it was performing. So you're saying from in 1-2 seconds the engine temp warmed the air up by 130-195 degrees? Ehh.. huh!?

You're theory about the engine not using certain sensors during the warmup period seems a lot more plausible to me.

 

[eco]

I am not saying that the motor and underhood air made the difference in performance, I am saying it does effect the air temp.

As far as the sensors, the temp sensors and the O2 are not used in open loop, but if they were failing they would likely cause poor economy and they would likely throw a code.

 

[TheRoadVirus]

Well, don't these engines run richer 'til they warm up? Hell, don't all engines?

 

[ACarbone624]

I notice that same pep when my truck first starts. After a few minutes its back to normal. I thought it was all in my head.

 

[O'Rattlecan]

I thought it had something to do with it still being in closed loop cycle until it warms up.

Ryan

 

[tomtoc]

mine seems like to opposite is true. it feels like a dog when it first starts. all rpms and nothing to show for it.

 

[msb71]

Mine is when the engine is cold , not just when it is cold outside. I start it up , wait 5 seconds, then put it in drive then go , spins the tires when I left the parking lot last night, ( pavement was dry), doesn't do that when it is warmed up.

 

[eco]

I thought it had something to do with it still being in closed loop cycle until it warms up.

Ryan

The computer is in OPEN LOOP when the motor is cold and the computer is in CLOSED LOOP when the motor has reached operating temp. In closed loop the computer is using feedback from all the sensors, in open loop the computer only uses a few sensors thus the computer can run the motor much better in closed loop. It sounds like you got your loops backwards.

 

[NeXtras]

engine being cold wont let t be peppier... the oil is vey thick when cold and your engine is trying to figh through the oil AND move the truck. If anything, it will be slower. It may SOUND better cause the rpms will come up quick, but its not.

 

[conanski]

The difference is performance is due to the fact the motor is open loop until it reached operating temperature. In open loop the computer adds more fuel, and an engine makes best power when the A/F ratio is slightly rich.. 13-13.5:1, as opposed to the 14.7:1 the EFI system targets in closed loop.

 

[msb71]

The difference is performance is due to the fact the motor is open loop until it reached operating temperature. In open loop the computer adds more fuel, and an engine makes best power when the A/F ratio is slightly rich.. 13-13.5:1, as opposed to the 14.7:1 the EFI system targets in closed loop.

Ok this makes sense, wish it was cold all the time ,,lol.