Does the thermometer calculate wind-chill?

[Radshooter]

When I left work tonight, I decided to go the long way home to get the engine good and warm for a change. Going through town, the overhead console thermometer read 27*. When I got out on Interstate and up to 75 mph, I looked up and it said 19*. When I got back to town (same town) and on the surface streets again, it went back to 27*. It was only 3 miles out to the Interstate ramp, and back 3 miles on Interstate. Can't believe there would be that much temp diff in only 3 miles. Just wondering if anyone else noticed anything like this... Thanks.

 

[Turbo Tim 1]

Only if the sensor was all wet, then you have the wet bulb effect and the evaporation of water will cool down the sensor. Were you in stop and go in town? If the truck sets when running the engine heat will transfer to the sensor, at least it used to on my 94.

 

[hammersley]

remember wind chill is a theory -

in that the actual air temperature never changes, i. e. that value is the same - if it's 20 degrees and no wind or 20 degrees and a 30 mph wind the temperature is still 20 degrees. The only difference is the dissapation of heat is very rapid with the wind - so the effect on warm bodies - animals - is estimated with the wind chill table.

 

[Turbo Tim 1]

Not to be combative but wind chill is not a theory it is the action that causes evaporative cooling. Take two old style liquid thermometers, place a coarse wet piece of cloth (like sock material) on one and nothing on the other then place them in front of a fan, the one with the wet rag will read cooler. Guaranteed

 

[David Oxland]

I always wondered if I got going fast enough if the temperature would begin to go up and the truck get a bit longer.

 

[Steve G]

While we are talking about the the overhead temp, is there a way to calibrate the temp? Mine is reads about 4 degrees high.



Steve

 

[zstroken]

Wind is a cooling effect but

Wind chill will cause an item to cool faster but it will not cause the item to be colder than it actually is. Wind chill is relative to 98. 6 degrees. If you look at the equation for convection heat transfer(wind chill) it will have a delta T in it. Once the object reaches the ambient temperature outside, then the Delta T is zero and you use the other forms of heat transfer on it.

 

[Crunch]

Originally posted by Radshooter

When I left work tonight, I decided to go the long way home to get the engine good and warm for a change. Going through town, the overhead console thermometer read 27*. When I got out on Interstate and up to 75 mph, I looked up and it said 19*. When I got back to town (same town) and on the surface streets again, it went back to 27*.

The thermometer on the overhead console has been the only real complaint I have had with my truck (purchased mid-July). From the day I drove it off the lot the overhead temp read 130*. We had a few periods during late summer where the temp dropped to the mid to upper 80s and it still read 130*. A couple of times we had rain, and the thermometer seemed to read the correct temperature, but after driving a few minutes it was back to 130*. When summer broke and we had a few real cold snaps (upper 40s to upper 50s--yeah, it's a Texas cold snap!) the thermometer read -34* a few times. Now it seems to be reading correctly, but I still plan to take it in to the dealer when I get a chance. When I told the service techs about it they got an "Oh no!" look on their face and said I would need to leave it with them for the day. They said they might have to replace the sensor. For the most part I couldn't care less about the outside temperature, but since it is a new truck I plan on taking it in when I get a day to spare. They suggested I make an appointment to ensure it gets done in one day. It sounds as if the actual fix is relatively easy, but pulling parts off to get to the fix point will be a PITA.

 

[AggieJustin]

When I told the service techs about it they got an "Oh no!" look on their face and said I would need to leave it with them for the day. They said they might have to replace the sensor. For the most part I couldn't care less about the outside temperature, but since it is a new truck I plan on taking it in when I get a day to spare. They suggested I make an appointment to ensure it gets done in one day. It sounds as if the actual fix is relatively easy, but pulling parts off to get to the fix point will be a PITA.

Not sure why the sensor should be such a big deal to replace. Isn't it still located right behind the grill on a bracket bolted to the hood? If so, it's just a simple R&R job.

 

[Vaughn MacKenzie]

Drastic temp changes

Speaking of temp changes last summer I was coming from Boise toward Pedleton Oregon and hit a rain squall at the top of Cabbage Hill. As I began my descent my overhead indicated 61F. Less than 10 miles later as I drove by Pendleton it read 97F. There was nothing wrong with my overhead, the temperature changed 36 degrees as I dropped 2000 feet into the valley.



Vaughn

 

[Crunch]

Originally posted by AggieJustin

Not sure why the sensor should be such a big deal to replace. Isn't it still located right behind the grill on a bracket bolted to the hood? If so, it's just a simple R&R job.

The impression I got was that as part of the diagnostic process they would also have to drop the console and maybe the headliner. When I mentioned it to a sales supervisor he thought it needed nothing more than a reflash, but the service techs thought it may be the senson, but no one knew for sure, hence the diagnostic process.

 

[DLeno]

I think you guys are confusing the term "wind chill" with the dry bulb - web bulb method of measuring relative humidity. Both utilize the same exact principle which is that higher rates of evaporation reduces temperature. thats why a can of gasoline is colder than the ambient temperature around it. stick a thermometer into one some time.



Yes, if you stick a mercury glass thermometer in a wet sock it will read cooler. yes, if the temp sensor under the hood is wet, it will read cooler at highway speeds due to evaporation.



higher air velocity next to an object increases the rate of evaporation from that object because it decreases the "vapor pressure". If the object is dry, there is nothing to evaporate and no reduction in temperature (vapor pressure is a don't care). If the object is wet (with something that evaporates, like water, paint thinner, whatever), the rate of evaporation determines the change in temperature.



Anyway, "wind chill" refers to the effect of high velocity wind against human skin and numerically expresses the physical condition corresponding to identical rates of energy transfer from skin to air. Since the rate at which energy leaves your skin determines the "feels like temperature" it is possible to calculate the wind velocity at which the energy transfer from your skin is equivalent to a lower air temperature with no wind.

 

[Ladders]

Crunch,

The sensor is by the drivers side headlite. Its easy to get at and if you have someone w/ a 3rd G close by, try a trade to ck it. Dont know if its the same sensor as the 2g's but might be for a trial. Also try some quick evaporating fluid on the sensor to see if it changes it (like a can of dry air - used upside down it will freeze). Just some ideas till you can get it to the dealer - at least you'll know what to tell the "deer-in-headlite-looking" tech. If that doesnt correct the problem then it might be the console or a re-flash. I would suspect the probe, maybe a loose wire/connection due to its location maybe even water.



SOTSU!!

\\BF//

 

[JDanford]

Cold-Colder-Coldest

Then, while you're at it, add into the equation the venturi effect; ie carburetor icing in an airplane.

 

[David Oxland]

small site here for you

http://linda.lawrie.com/windchill.html

and here

http://www.delphiforfun.org/Programs/windchill.htm

 

[radar doctor]

Wet Bulb Dry Bulb Weather Data

Now that we have heard the theroy from ,I expect ,must be two, guy's here that were connected with the National Weather Service, I wonder if my truck will run faster in a wet or a dry situation???How about that Mr Dlino and Mr Turbo Tim???Anyway ,You did a Nice Job and the way i see it, No matter how you Skin a Cat, THE CAT, AIN'T GONNA THINK MUCH OF IT... .

 

[hammersley]

BUT there is still another factor about WINDCHILL

and our trucks - and that is Mr. T - no not that Guy - I mean Time. Take 2 trucks and turn them off at the same time, and park them overnight exposed to th esame temperatures, EXCEPT that one is left in the wind. Now depending on how the wind can get at the engine compartment, this truck will be colder longer in the AM when you try to start her. The wind removes the heat faster. That's why you blow on hot soup, etc.

 

[DLeno]

correct, but that is not windchill itself due to evaporation, that is simple energy transfer from hot to cold. When the air is moving across a warm surface, the temperature difference between the two (warm engine next to cold air) is greater because the engine is always next to "cold" air molecules. and the greatest rate of energy transfer from hot to cold occurs when the temperature difference is the greatest. so yea, blow on your soup, stirr your coffee, all of those things maximize energy transfer by maximizing temperature difference.



The way in which this is different from wind chill and evaporation is this: after the engine sits all night and becomes the same temperature as the surrounding air, no matter how hard the wind blows, the engine will never be colder than the air temperature (ideally of course). But if you put some volitile liquid on the engine, then it starts to evaporate and the engine now can become colder than the air.



For the same reason, the temperature sensor itself, if perfectly dry, always follows the air temperature regardless of wind speed. Now then, if you quickly move from a hot environment to a cooler one, then the temp sensor (because its mass is not zero) has to cool down (release heat energy into the air) and this is just like cooling off an engine in the wind (except that the temp sensor is smaller... ).

 

[hammersley]

is it possible that the temperature probe for

the thermometer, in the cab, is getting wet???? Not sure where it is located. My truck doesn't have this feature... .

 

[NC_Mog]

Originally posted by DLeno

The way in which this is different from wind chill and evaporation is this: after the engine sits all night and becomes the same temperature as the surrounding air, no matter how hard the wind blows, the engine will never be colder than the air temperature (ideally of course).

I've agreed with all your posts, except this one. On a clear night, your truck can get colder than the ambient air temperature. Its called radiant heat transfer and is why you get frost on your window when its above freezing outside.