Wind chill really doesn't make a difference?

[RamFan]

I know that "feels like" temperature doesn't have an affect on inanimate objects, but...

Bridges freeze before roads do because the wind which passes beneath and above the bridge wisks away heat from the road. Couldn't a similar affect occur to our engines when driving in cold weather? If the temperature is 32* but the temperature with windchill is 12* an engine would probably have a harder time warming up than if the temperature were simply 32* with no windchill. Not because of the windchill temperature but because of the wind that is occuring. More cold wind is present to take away heat from the vehicle.

Am I just way off here or is this possible?

 

[Rand]

a basic kernel of truth but in reality its not much difference.. you are already driving around

so you always have "wind chill" on car anyway



now if you are sitting there idling to warm up..

in calm vs a 50mph wind blowing on your car..

yes you might notice some difference.

 

[Quattro Pete]

Originally Posted By: RamFan
Bridges freeze before roads do because the wind which passes beneath and above the bridge wisks away heat from the road.

Not exactly. Bridges freeze before roads because they are surrounded by ambient temp air that's both above the bridge and below the bridge. So the bridge construction takes less time to reach outside ambient air temp, but it doesn't become any colder than air temp in the process. On the other hand, roads are kept warmer due to soil that's underneath the road. That soil typically takes a lot longer to drop in temp.

 

[kschachn]

Quattro Pete is correct. There's a difference in "wind chill" and what is happening with a bridge. Wind chill is a perception in what the temperature feels like to you as opposed to how long it takes an object to reach ambient temperature.

If you drive your car and it is all warmed up, when you stop it takes more or less time to reach ambient depending on the wind (and direction). If there is a stiff wind blowing directly on the front of the car it's going to take less time for the car to cool down since the wind is taking the heat away quickly. If there is no wind then it will take longer.

It will still only reach the ambient temperature however. It's going to feel colder to you (with exposed skin that is) with that wind, but the car isn't going to get any colder than the actual temperature.

 

[KrisZ]

Wind chill can have an effect in warm up time. If you park a car facing the wind, it will definitely warm up longer than with no wind, but once you start driving the wind chill factor is always there.

Wind simply helps with heat transfer.

 

[javacontour]

Bingo!

Originally Posted By: Quattro Pete
Originally Posted By: RamFan
Bridges freeze before roads do because the wind which passes beneath and above the bridge wisks away heat from the road.

Not exactly. Bridges freeze before roads because they are surrounded by ambient temp air that's both above the bridge and below the bridge. So the bridge construction takes less time to reach outside ambient air temp, but it doesn't become any colder than air temp in the process. On the other hand, roads are kept warmer due to soil that's underneath the road. That soil typically takes a lot longer to drop in temp.

 

[javacontour]

Probably not much. The thermostat will not open until the coolant in the engine gets warm enough. There may be some air passing over the engine block and head(s) but I don't think it will be much with everything else it passes through prior to the engine.

Now when the thermostat finally opens and coolant flows through the radiator, it will cool off quicker if there is more airflow due to driving into the wind.

But I can't see it really making that big of a difference in the time for the engine to warm it's oil and coolant.

Originally Posted By: KrisZ
Wind chill can have an effect in warm up time. If you park a car facing the wind, it will definitely warm up longer than with no wind, but once you start driving the wind chill factor is always there.

Wind simply helps with heat transfer.

 

[RamFan]

Originally Posted By: kschachn

If you drive your car and it is all warmed up, when you stop it takes more or less time to reach ambient depending on the wind (and direction). If there is a stiff wind blowing directly on the front of the car it's going to take less time for the car to cool down since the wind is taking the heat away quickly. If there is no wind then it will take longer.



That's exactly what I was thinking, just using cold to hot versus hot to cold. I know the temperature of the block or anything else for that matter doesn't get colder than what the ambient temperature is, I just wasn't sure if the wind would have an impact on on how quickly it warmed up due to heat being blown away quicker than with no wind.

Thank you for all the quick responses!

 

[dparm]

Wind chill is all about human perception. If you're talking about convection on an engine block, that's a different thing.

 

[kschachn]

Yeah, it's basically forced convection. Same reason a convection oven cooks faster than a regular one.

Unless you are operating your car in a vacuum of course

 

[440Magnum]

Originally Posted By: RamFan
I know that "feels like" temperature doesn't have an affect on inanimate objects, but...

Bridges freeze before roads do because the wind which passes beneath and above the bridge wisks away heat from the road. Couldn't a similar affect occur to our engines when driving in cold weather? If the temperature is 32* but the temperature with windchill is 12* an engine would probably have a harder time warming up than if the temperature were simply 32* with no windchill. Not because of the windchill temperature but because of the wind that is occuring. More cold wind is present to take away heat from the vehicle.

Am I just way off here or is this possible?



"Wind chill" doesn't make a shut-down engine get any colder overnight than it would without the wind. If the actual temperature is 0F, and the wind chill is -40F and you leave the car parked in it for 12 hours, the engine block will be 0F. NOT -40F.

So wind can never make anything COLDER than the ambient temperature.

But if the engine is running, generating heat, and is WARMER than the surrounding air, blowing a 100 mph 0F wind across it will remove heat from it faster than calm 80-degree air around it. So the thermostat will open less, far less coolant will circulate thru the radiator etc. And when you shut it down, it will cool off quicker in a wind than without wind. The process of heat removal due to moving air (or any other fluid) falls under the category of convection, even though we usually think of convection as air moving on its own due to getting warmer. That separates it from the process of radiative cooling, which is infrared emission.

So: wind DOES affect any object that is warmer than the surrounding air, but it does NOT affect an object that is already the same temperature as the surrounding air.

 

[KrisZ]

Originally Posted By: javacontour
Probably not much. The thermostat will not open until the coolant in the engine gets warm enough. There may be some air passing over the engine block and head(s) but I don't think it will be much with everything else it passes through prior to the engine.

Now when the thermostat finally opens and coolant flows through the radiator, it will cool off quicker if there is more airflow due to driving into the wind.

But I can't see it really making that big of a difference in the time for the engine to warm it's oil and coolant.


You'd be surprised how little heat modern engines generate when idling. I remember few years ago we had a big snow storm and in the morning when it came to move the cars, to start shoveling the snow, I just left my Mazda running. It wasn't even that cold, maybe -10C, and the car was idling for about 20 minutes with the fan set on 1 to warm up the cabin and the temperature gauge only went a quarter way up (fully warmed up is half way). If there was a strong wind or the temperature was lower, the needle would probably stay in the cold zone.

I guess with heater off and nothing else taking away the heat, it probably makes little difference.

 

[Donald]

If a chunk of metal is being heated and there is no wind, its cooled by convection. The greater the difference between the temp of the metal and the air the better. However if wind is blown across the chunk of it will cool even faster than convection.

 

[GearheadTool]

If this were true, then engines would overheat easier in the summer, from all that hot wind.

 

[ARCOgraphite]

Engine "Body" temp is referenced ~ 100 deg F warmer than OUR bodies, so even the 100F deg Arizona dry heat is a big cold Delta. BUT ... warm, still air is less dense so it cannot remove heat as fast as in the mutually beneficial cooler + denser ambient conditions.

To answer part of your original Q, "Windchill" is a human perception of ambient conditions due to perspiration (evap cooling) and skin sensitivity which give the impression of a "cooler than gauge" environment. A warm block of iron will reach equilibrium with the ambient temp, then go no lower regardless of wind buffeting. It WILL, though, cool faster in the wind.
As a related aside, You can make your machine cool DOWN much faster (id est: remove Heat faster) by making some artificial "sweat" by spraying the block and rad core with water mist - then add kinetic wind buffeting. Works as long as the water doesnt freeze

 

[kschachn]

They do overheat easier in the summer. It's all about delta T, although in a properly functioning cooling system there is enough margin to allow adequate cooling even in Death Valley. But yeah your thermostat is going to be more open in summer because less heat is being extracted from the radiator than in the winter (for a given speed, etc.)

I have worked for a couple of electrical generating facilities in the past. At one they used cooling towers to condense the steam. It's a bit different since cooling towers also rely on evaporative heat loss, but still it's similar. In the winter we would have to run only one tower as opposed to all four in the summer. If it was really hot (and humid, back to the evaporative cooling) they would have to cut capacity a bit but that only happened once while I worked there.

Originally Posted By: GearheadTool
If this were true, then engines would overheat easier in the summer, from all that hot wind.

 

[MolaKule]

Quote:
However if wind is blown across the chunk of it will cool even faster than convection.


There are two kinds of convection, natural convection and forced convection.

Forced convection is when an external source of air flow is forced across the surface. Either way, it is still convection.

 

[dparm]

Wind chill is also due to the fact that our skin contains moisture. Last I checked, engine blocks don't sweat.

 

[MolaKule]

Quote:
Wind chill is also due to the fact that our skin contains moisture. Last time I checked, engine blocks don't sweat.


And last time I looked at my engine or transmission, it didn't have any goose bumps.

 

[rjundi]

If I park my Acura MDX in a non insulated barn that fits 9 vehicles the vehicle stays warmer inside and the engine temp too at restart.

Outside in the howling winds the car is not only colder in the interior but engine is not as warm if at all. There is wind (chill) is cooling the engine and interior quicker outside.

The temperature inside and out of barn is within a few degrees of each other.