What Causes Outside Temp. Readings to Skyrocket?

[kshapiro]

Like yesterday...mine read 114 degrees when I came out of the pool to my MINI in the parking lot. Sure, I know...the temp of the lot inself was high...radiating lots of degrees, but five miles later it was still too high (like 105 on a 98 day). Is the sensor or something near it holding heat? Are others expereincing the same?

[AprilWhine]

I think it's reading the temperature correctly. When it hit 103 here on Tuesday, my MINI was reading about 110. Since the temp tends to be hotter on pavement, that sounds about right to me. I don't think wind chill applies to inanimate objects so it wouldn't matter if you were parked or driving.

[Shep]

I have installed outside temperature gages on my other (non-MINI) cars ($20 to $50 accessories from Brookstone etc.).

Depending on where the MINI's outside sensor is located (I put mine on the painted steel bodywork in the door jamb of my Subaru and Honda) it will pick up the temperature of the surface it's attached to. If my car is in the shade, the temp reading is pretty accurate. If the sun is blazing down on the same side of the car as the sensor, it reads way too high. As you drive along, the airflow slowly cools the metal down, and the temp. reading drops.

To some degree, this is an insoluble problem. If you still get crazy readings on a cloudy day, there is something wrong with the device. Otherwise, you may have to live with it.

The greatest use for these temperature indicators, of course, is to warn you of near-freezing conditions so as to be aware of the dreaded black ice.

[BruceK]

I noticed this exact problem last evening when I pulled my car out of the garage to run some errands. I parked the car in the closed garage after driving home from work when the temperature was about 97F. Even several hours later while sitting in a closed garage with a hot engine the temp reading was 99F when I started the car. I pulled the car out and by now the sun had set and the ambient temperature felt like it was in the low 90's, so I opened the sunroof and windows for my drive.

I could feel the temperature lowering as I drove through different residential areas, but the temp displayed by the car was very slow to respond and still indicated upper 90's F dropping a degree only every several minutes. After about 15 minutes of driving did the temp finally drop down to 90F.

My thoughts are the temp sensor is mounted on something that acted as a heat sink (or the car itself was the heat sink) which prevented accurate readings being shown even though the surrounding air was almost 10 degrees F cooler. After the hot car lowered it's temperature the sensor finally read acurately.

[minirall]

A basic explanation for the high temperature reading is because of Infra-Red Radiation. You know that glass allows light through into the car. It also allows IR radiation (heat) through. The glass also prevents UV radiation from getting through. That's why you cant get sunburned from driving in a car with the windows up, but you still can get hot. The glass lets the heat in but it will not let it back out. Your temp reading is high, because of concentrated heat by the sensor. Eventually the airconditioning will lower the temperature of the air surrounding the sensor.
Hope that helps.

[BruceK]

Quote:

Originally posted by minirall
A basic explanation for the high temperature reading is because of Infra-Red Radiation. You know that glass allows light through into the car. It also allows IR radiation (heat) through. The glass also prevents UV radiation from getting through. That's why you cant get sunburned from driving in a car with the windows up, but you still can get hot. The glass lets the heat in but it will not let it back out. Your temp reading is high, because of concentrated heat by the sensor. Eventually the airconditioning will lower the temperature of the air surrounding the sensor.
Hope that helps.

I don't think we're talking about the same thing here. Other people in this thread are discussing the temp reading that appears in window within the tachometer designed to show the exterior ambient temperature.

Perhaps your thinking of the interior temperature sensors used to help regulate the MINI's climate control (a/c and heating) system? Those sensors have to deal with the 'greenhouse effect' of energy in the form of light passing through the windows, but energy in the form of heat being radiated off of the interior being trapped by those same windows (and doors and roof, etc.)_

[dietcokeplease]

Bruce,

My experience with OTG on cars are that they do not tend to show or allow rapid changes in temp. This isn't a bad thing but rather a designed feature. It is meant to show average ambient temp over a period of time - say 10-15mins.

Otherwise, say you can to a halt in traffic, with the fans and engine heat and anothers cars exhaust in front of you this would allow the temp to give a false reading of a localised spot.

I've found that OTGs are fairly accurate devices and can be relied upon.

DC

[m1les]

The outside air temperature sensor is located to the top of the front bumber mesh. The auto AC is probably controlled from this so as DC says, the electronics will be designed to stop any hunting.

[kshapiro]

Quote:

Originally posted by AprilWhine
I think it's reading the temperature correctly. When it hit 103 here on Tuesday, my MINI was reading about 110. Since the temp tends to be hotter on pavement, that sounds about right to me. I don't think wind chill applies to inanimate objects so it wouldn't matter if you were parked or driving.

Wind chill will not effect it, but when you're driving it's measuring the air That'soving past the sensor as opposed to the air rising up off the balck asphalt of the parking lot. So, yes...it does go down after you drive off.

[AprilWhine]

Quote:

Originally posted by kshapiro


Wind chill will not effect it, but when you're driving it's measuring the air That'soving past the sensor as opposed to the air rising up off the balck asphalt of the parking lot. So, yes...it does go down after you drive off.

Sorry Ken, but that air moving past the sensor just rose off the pavement...

[kshapiro]

Quote:

Originally posted by AprilWhine


Sorry Ken, but that air moving past the sensor just rose off the pavement...

and the grass nearby...give it a try..sit in your car at the local K-Mart for two hours with the windows closed...just as you're getting ready to die, pull away (windows still up) and drive...the temp. in the car will go down. Or, safer method...watch the temp. sensor on your MINI go down in the same situation, That's what prompted this discussion in the first place.

[COOPERation]

OK, Ken, I've been here at K-Mart for about an hour now, damn it's hot in here with the windows up...I'll let you know in an hour if you're right. If you don't hear from me...well than...something went horribly wrong...whew...

[kshapiro]

Quote:

Originally posted by COOPERation
OK, Ken, I've been here at K-Mart for about an hour now, damn it's hot in here with the windows up...I'll let you know in an hour if you're right. If you don't hear from me...well than...something went horribly wrong...whew...

No..No..STOP..it was a trick to do in AprilWhine...roll down the windows...I didn't mean to hurt you...

[AprilWhine]

Quote:

Originally posted by COOPERation
OK, Ken, I've been here at K-Mart for about an hour now, damn it's hot in here with the windows up...I'll let you know in an hour if you're right. If you don't hear from me...well than...something went horribly wrong...whew...

STAY AWAY FROM THE LIGHT! For God's sake, stay away from the light!

[Sejanus]

What Causes Outside Temp. Readings to Skyrocket?

Driving from SF to Sacramento in August.

Seriously though, driving between the Bay Area and the Sacramento Valley you do experience some fairly rapid temp. changes and the outside temp gauge seems to be dead on to me.