Should my car feel slower with a cold engine
Discussion
OverSteery said:
GloriaGTI said:
Surely at motorway speed it will take that long, as the engine is going to be turning over at lower revs, no?
No - its the heat of the combustion that provides the majority of the heat, so the engine speed isn't that relevant. if there is lots of fuel going in then there will be heat. A large 4x4, for example, pushing a huge hole in the air will heat up nice a quickly at 75 even with interstellar gearing. 
The Oversteery comment above is confused and contradictory.
1. Engine load due to revs 'isn't that relevant'
2. Enigine load due to poor aero is relevant?
One static combustional rotation of a particular engine will produce x amount of heat. The more of these there are in rapid succession, the faster the engine will heat up.
The faster the engine turns over, the more heat there is, which is wasted energy (mostly)
Yes, combustion is hot, but friction causes massive amounts of heat.
As an experiment, if you'd like to heat an engine up really quickly, you would drive a laden vehicle at the maximum sensible revs for the cold engine in 1st gear, up a hill.
A horrible thing to do yes. Adding mass as ballast, adding further load due to incline, revs / friction, poor cooling due to slow airflow into rads.
So yes, revs = heat as they increase workload and friction hugely.
As the the question from the OP?
Rich running, thick oil (higher friction) are the main inefficiencies when the engine is cold.
Ecu programming will also play a part, as to make the car feel even more reluctant to accelerate.
I've seen in several handbooks, this having a failsafe though.
If you absolutely demand full power and floor it, the ecu will then allow max power, (whatever is max is available due to above mentioned inefficiency when cold) as an emergency measure.
Mave said:
Running the engine leaner and leaner doesn't make combustion hotter and hotter ad infinitum. Once it is leaner than stoichiometric, the combustion cools down again. All you are then doing with the additional air is diluting the hot, close-to-stoichiometric burning zone with cooler air, bringing the overall charge temperature down. If putting less fuel in led to higher and higher charge temperatures, then you'd get more power the less fuel you put in!
I didn't say the temperature is rpm dependent at all, I said it was throttle (or accelerator) position dependent. The combustion cycle changes dependent on accelerator position. At a given rpm, more accelerator pedal = more fuel = hotter charge = more area under the curve when you look at the thermodynamics (discounting the turbocharger effect on the cycle)
http://www.open.edu/openlearn/science-maths-technology/transport-and-sustainability/content-section-3I didn't say the temperature is rpm dependent at all, I said it was throttle (or accelerator) position dependent. The combustion cycle changes dependent on accelerator position. At a given rpm, more accelerator pedal = more fuel = hotter charge = more area under the curve when you look at the thermodynamics (discounting the turbocharger effect on the cycle)
You cannot ignore p v t gas laws, its under more compression ergo it IS HOTTER unless you are redefining the laws of physics.
A petrol engine goes through more cycles so will dissipate more heat but on a single combustion cycle the cylinder temps before and during combustion are hotter on a diesel.
Here you go http://www.open.edu/openlearn/science-maths-techno...
Diesel combustion is at a higher temp than petrol
Red 5 said:
As an experiment, if you'd like to heat an engine up really quickly, you would drive a laden vehicle at the maximum sensible revs for the cold engine in 1st gear, up a hill.
A horrible thing to do yes. Adding mass as ballast, adding further load due to incline,
I think the point was, it's load on the engine (in terms of how much power it is making) that warms an engine up. In your examples, you're citing ways to increase the power demand on the engine- and I expect that if the engine can pull max revs up the hill in first, then you'll actually warm it up quicker in second because you'll be able to keep the throttle wide open and make more power.A horrible thing to do yes. Adding mass as ballast, adding further load due to incline,
M-SportMatt said:
Mave said:
Running the engine leaner and leaner doesn't make combustion hotter and hotter ad infinitum. Once it is leaner than stoichiometric, the combustion cools down again. All you are then doing with the additional air is diluting the hot, close-to-stoichiometric burning zone with cooler air, bringing the overall charge temperature down. If putting less fuel in led to higher and higher charge temperatures, then you'd get more power the less fuel you put in!
I didn't say the temperature is rpm dependent at all, I said it was throttle (or accelerator) position dependent. The combustion cycle changes dependent on accelerator position. At a given rpm, more accelerator pedal = more fuel = hotter charge = more area under the curve when you look at the thermodynamics (discounting the turbocharger effect on the cycle)
You cannot ignore p v t gas laws, its under more compression ergo it IS HOTTER unless you are redefining the laws of physics. I didn't say the temperature is rpm dependent at all, I said it was throttle (or accelerator) position dependent. The combustion cycle changes dependent on accelerator position. At a given rpm, more accelerator pedal = more fuel = hotter charge = more area under the curve when you look at the thermodynamics (discounting the turbocharger effect on the cycle)
Mave said:
Red 5 said:
As an experiment, if you'd like to heat an engine up really quickly, you would drive a laden vehicle at the maximum sensible revs for the cold engine in 1st gear, up a hill.
A horrible thing to do yes. Adding mass as ballast, adding further load due to incline,
I think the point was, it's load on the engine (in terms of how much power it is making) that warms an engine up. In your examples, you're citing ways to increase the power demand on the engine- and I expect that if the engine can pull max revs up the hill in first, then you'll actually warm it up quicker in second because you'll be able to keep the throttle wide open and make more power.A horrible thing to do yes. Adding mass as ballast, adding further load due to incline,
More power does indeed = more load, but comes with greater speed and cooling over the rads. Then we'd be talking about efficiency of cooling systems on cirtain engines yes?
I know that this can be taken to extremes, to make the point....
5 mins flat out in top gear won't tend to overheat an engine.
5 mins at high revs in first gear often will
So even though less load is being applied, the systems designed to remove heat, are just not efficient at such slow speeds.
M-SportMatt said:
You cannot ignore p v t gas laws, its under more compression ergo it IS HOTTER unless you are redefining the laws of physics.
Correct... while you're considering the compression of a gas (including a gas with an atomised liquid in suspension).But as soon as that atomised liquid ignites, the gas laws take a back seat when it comes to determining the temperatures.
TooMany2cvs said:
Correct... while you're considering the compression of a gas (including a gas with an atomised liquid in suspension).
But as soon as that atomised liquid ignites, the gas laws take a back seat when it comes to determining the temperatures.
This has got a bit off topic, but yes i was just pointing out to the poster that diesel combustion is not cooler than petrol however more efficient it is. Which is true.But as soon as that atomised liquid ignites, the gas laws take a back seat when it comes to determining the temperatures.
Petrol is less efficient in terms of wasted heat (albeit at lower temps), however there are many more cycles of petrol combustion (higher rpm) therfore a much greater amount of energy is wasted as heat by petrol engines.
Pan Pan Pan said:
Even at the motorway speed limit, my diesel Passat is still turning at less than 2000 rpm, and for non motorway driving it can take up to 20 to 30 minutes for the cooling system to reach normal operating temperature,
Surprisingly after just half a mile or so, the heating system `can' put out warm air, but with the exception of the screen clearing setting.
Sounds to me like your thermostat is not closing properly at low temps... Surprisingly after just half a mile or so, the heating system `can' put out warm air, but with the exception of the screen clearing setting.
Back to the topic....
My engine temp can show as 90 on the gauge (in my VW that means a coolant temp of higher than 75 degree C) - All VW's do this.
At this point sometimes my oil temp is still in the high 40s/ low 50s.
I do not drive hard until oil temp is up to at least 70 degree C. This can often be 10-15 minutes of driving.
My engine temp can show as 90 on the gauge (in my VW that means a coolant temp of higher than 75 degree C) - All VW's do this.
At this point sometimes my oil temp is still in the high 40s/ low 50s.
I do not drive hard until oil temp is up to at least 70 degree C. This can often be 10-15 minutes of driving.
M-SportMatt said:
This has got a bit off topic, but yes i was just pointing out to the poster that diesel combustion is not cooler than petrol however more efficient it is.
But that's not relevant to the poster, because charge temperature rather than combustion temperature is the more important consideration when talking about warm up times.xjay1337 said:
Back to the topic....
My engine temp can show as 90 on the gauge (in my VW that means a coolant temp of higher than 75 degree C) - All VW's do this.
At this point sometimes my oil temp is still in the high 40s/ low 50s.
I do not drive hard until oil temp is up to at least 70 degree C. This can often be 10-15 minutes of driving.
+1 for this.My engine temp can show as 90 on the gauge (in my VW that means a coolant temp of higher than 75 degree C) - All VW's do this.
At this point sometimes my oil temp is still in the high 40s/ low 50s.
I do not drive hard until oil temp is up to at least 70 degree C. This can often be 10-15 minutes of driving.
My GTI coolant can be showing 90dC after 10 mins but the oil temp gauge may not even be reading 50 dC after 15mins.
I won't use the loud pedal, unless required to, until my oil temp is above 80dC.
hman said:
Pan Pan Pan said:
Even at the motorway speed limit, my diesel Passat is still turning at less than 2000 rpm, and for non motorway driving it can take up to 20 to 30 minutes for the cooling system to reach normal operating temperature,
Surprisingly after just half a mile or so, the heating system `can' put out warm air, but with the exception of the screen clearing setting.
Sounds to me like your thermostat is not closing properly at low temps... Surprisingly after just half a mile or so, the heating system `can' put out warm air, but with the exception of the screen clearing setting.
Sometimes on here I do wonder, like oil changes, needs one every 40 miles or every hour, whichever is the sooner and then warming it up, start it in March and by May you should be ok to go to half throttle, but only if the oil is at 90 C or over and its been changed that morning.
I have more mechanical sympathy than most and change oil religiously, check it regularly, clean, polish, fit decent tyres and fettle, but I wait for my car to get its oil round and be showing its on its way up to temperature before any throttle, but if I need to, I give it a bootful, as long as its not stone cold, clean oil is circulating it will be fine, and if its not, I will buy another, never killed an engine or even remotely aged it as far as I can tell.
Life is too short on you average motor to fanny about waiting for oil temps, 20 miles ffs, would rather kill it than do that, cars exist for my utility, comfort and convenience, I am not its servant. Maybe with a Ferrari F40 I may be more circumspect but an old Merc CLS ? nah, it will be fine for another 200k with my approach, something else will kill it way before the engine dies.
Even the mechanically ignorant and insensitive only usually kill engines via not ever topping the oil up.
People get all indignant about these things, then when there is something about road safety or emossions, which actually matters, they say "Wont someone think of the children".
I have more mechanical sympathy than most and change oil religiously, check it regularly, clean, polish, fit decent tyres and fettle, but I wait for my car to get its oil round and be showing its on its way up to temperature before any throttle, but if I need to, I give it a bootful, as long as its not stone cold, clean oil is circulating it will be fine, and if its not, I will buy another, never killed an engine or even remotely aged it as far as I can tell.
Life is too short on you average motor to fanny about waiting for oil temps, 20 miles ffs, would rather kill it than do that, cars exist for my utility, comfort and convenience, I am not its servant. Maybe with a Ferrari F40 I may be more circumspect but an old Merc CLS ? nah, it will be fine for another 200k with my approach, something else will kill it way before the engine dies.
Even the mechanically ignorant and insensitive only usually kill engines via not ever topping the oil up.
People get all indignant about these things, then when there is something about road safety or emossions, which actually matters, they say "Wont someone think of the children".
J4CKO said:
I have more mechanical sympathy than most and change oil religiously, check it regularly, clean, polish, fit decent tyres and fettle, but I wait for my car to get its oil round and be showing its on its way up to temperature before any throttle, but if I need to, I give it a bootful, as long as its not stone cold, clean oil is circulating it will be fine, and if its not, I will buy another, never killed an engine or even remotely aged it as far as I can tell.
.
Exactly, an nice ester based oil to spec will be fine. Most cars die of other things than the engine wearing out. .
J4CKO said:
Sometimes on here I do wonder, like oil changes, needs one every 40 miles or every hour, whichever is the sooner and then warming it up, start it in March and by May you should be ok to go to half throttle, but only if the oil is at 90 C or over and its been changed that morning.
I have more mechanical sympathy than most and change oil religiously, check it regularly, clean, polish, fit decent tyres and fettle, but I wait for my car to get its oil round and be showing its on its way up to temperature before any throttle, but if I need to, I give it a bootful, as long as its not stone cold, clean oil is circulating it will be fine, and if its not, I will buy another, never killed an engine or even remotely aged it as far as I can tell.
Life is too short on you average motor to fanny about waiting for oil temps, 20 miles ffs, would rather kill it than do that, cars exist for my utility, comfort and convenience, I am not its servant. Maybe with a Ferrari F40 I may be more circumspect but an old Merc CLS ? nah, it will be fine for another 200k with my approach, something else will kill it way before the engine dies.
Even the mechanically ignorant and insensitive only usually kill engines via not ever topping the oil up.
People get all indignant about these things, then when there is something about road safety or emossions, which actually matters, they say "Wont someone think of the children".
Especially when it's something utterly prosaic like a bloody Golf.I have more mechanical sympathy than most and change oil religiously, check it regularly, clean, polish, fit decent tyres and fettle, but I wait for my car to get its oil round and be showing its on its way up to temperature before any throttle, but if I need to, I give it a bootful, as long as its not stone cold, clean oil is circulating it will be fine, and if its not, I will buy another, never killed an engine or even remotely aged it as far as I can tell.
Life is too short on you average motor to fanny about waiting for oil temps, 20 miles ffs, would rather kill it than do that, cars exist for my utility, comfort and convenience, I am not its servant. Maybe with a Ferrari F40 I may be more circumspect but an old Merc CLS ? nah, it will be fine for another 200k with my approach, something else will kill it way before the engine dies.
Even the mechanically ignorant and insensitive only usually kill engines via not ever topping the oil up.
People get all indignant about these things, then when there is something about road safety or emossions, which actually matters, they say "Wont someone think of the children".
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