Outside temperature reading
07-02-2004, 01:01 PM
#1
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Outside temperature reading
Ok..
So I'm reposting a year old question:
Why is the outside temperature reading off (as in, incorrect) regardless as to whether the car is standing still, driving on the freeway 80 mph, or sitting in traffic under pouring rain.
I've mentioned this to my dealer, and they tell me that it's "normal"! That the temperature reading depends on the ambient temperature (duh!) and is affected by the heat emanating from the road, etc. What good is an ambient temperature sensor, that gives you a false ambient temperature reading? I don't want to know how hot the road is, I want to know what's the current temperature!
The few posts that I've read on this topic indicate that there is no way to calibrate this; but why are there others that do not have this problem?
This is my second e500 (after totalling my previous) and I've had the same issue on both.
What gives?
So I'm reposting a year old question:
Why is the outside temperature reading off (as in, incorrect) regardless as to whether the car is standing still, driving on the freeway 80 mph, or sitting in traffic under pouring rain.
I've mentioned this to my dealer, and they tell me that it's "normal"! That the temperature reading depends on the ambient temperature (duh!) and is affected by the heat emanating from the road, etc. What good is an ambient temperature sensor, that gives you a false ambient temperature reading? I don't want to know how hot the road is, I want to know what's the current temperature!
The few posts that I've read on this topic indicate that there is no way to calibrate this; but why are there others that do not have this problem?
This is my second e500 (after totalling my previous) and I've had the same issue on both.
What gives?
07-02-2004, 01:20 PM
#2
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'08 AM Vantage V8 - '03 E500
Just out of curiosity, why do you assume that the temp reading in your car is incorrect? If it doesn't agree with the time/temperature sign on the bank that you just drove by, it's entirely possible that the sign is incorrect. The temperature reading on my W211 seems to be highly accurate. When the car is on a freeway with the sun baking down (the default condition around here for six months of the year) the indicated temperature might be five degrees higher than in the heavily-shaded neighborhood where I live. That doesn't mean the readings are incorrect; the air over the freeway will be several degrees hotter because of the heat radiating from the road and shed by the cars on the road.
07-02-2004, 01:47 PM
#3
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Originally Posted by DWP
The temperature reading on my W211 seems to be highly accurate. When the car is on a freeway with the sun baking down (the default condition around here for six months of the year) the indicated temperature might be five degrees higher than in the heavily-shaded neighborhood where I live. That doesn't mean the readings are incorrect; the air over the freeway will be several degrees hotter because of the heat radiating from the road and shed by the cars on the road.
But.. accurate in relation to what? And.. what about when it's cold outside and the temperature reading is still off? Heat rises, so sure, I can see how radiant heat might transfer to the sensor.. but when it's cold, or when you're doing 80 mph on the freeway.. or when you compare it against your girlsfiends BMW x5 and her reading reflects more closely what the forecast for the day was.. well, you catch my drift.
If your reading is accurate, then that just reinforces my peeve. WHY ISN'T MINE!
07-02-2004, 01:49 PM
#4
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2004 E500
Several times, I have checked my indoor/outdoor thermometer before leaving the house and found the Benz agreed. Also, I live about one mile from Reagan National Airport which is what the local radio stations use for their weather reports and it agrees with that also. As DWP reports, you can get a large variation depending on whether it is on the road, in the shade, etc.
07-02-2004, 01:52 PM
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When you look at your outside temperature indicator, what you are looking at is an "instantaneous" reading, or the reading the sensor is measureing at that second. If your car had been driven & then parked for a little while there would be extra residual heat trapped under the hood from the engine, reflected parking lot heat, etc.
The proper way to use the readout is to drive the car around for a while, let it sample a lot of temperatures, get rid of that horrid trapped engine heat, & then read it.
If you had a thermometer on your patio located in direct sunlight, it would read high all the time also. Likewise if it we always in the shade, it would read low. Mix all that in with the fact that there are slight variences in the accuracy of ALL thermometers, and variences can be induced by other factors such as elevation, location of the sensor relative to the display, humidity, etc, and then you'll understand.
I've seen my temp display read 78 in the winter after a quick bite in a fast food joint... (underhood heat) after driving a few minutes it went down to the 50's.
You don't want an "instantaneous" reading, you want an average temp.
The proper way to use the readout is to drive the car around for a while, let it sample a lot of temperatures, get rid of that horrid trapped engine heat, & then read it.
If you had a thermometer on your patio located in direct sunlight, it would read high all the time also. Likewise if it we always in the shade, it would read low. Mix all that in with the fact that there are slight variences in the accuracy of ALL thermometers, and variences can be induced by other factors such as elevation, location of the sensor relative to the display, humidity, etc, and then you'll understand.
I've seen my temp display read 78 in the winter after a quick bite in a fast food joint... (underhood heat) after driving a few minutes it went down to the 50's.
You don't want an "instantaneous" reading, you want an average temp.
07-02-2004, 03:39 PM
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My assumption has been with these electronic temperature gauges is that they are compensating in some way. Anywhere on the car will not really represent a true outdoor temperature, so, I'm assuming that they build an algorithm to adjust the temperature. I have no idea where the temperature sensor is.
I've seen some crazy temps too. When it was 10-20 F outside, and my unheated garage was like 15-25 F, the temperature would be WAY off, and I'd have to wait fo the car to warm up before I could get an accurate temp. My friend has an SL, and we have compared the temps, and both of ours are about 2-4 degrees off from each other.
I've seen some crazy temps too. When it was 10-20 F outside, and my unheated garage was like 15-25 F, the temperature would be WAY off, and I'd have to wait fo the car to warm up before I could get an accurate temp. My friend has an SL, and we have compared the temps, and both of ours are about 2-4 degrees off from each other.
07-02-2004, 04:08 PM
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I know on GM cars the sensor is located just forward of the radiator. Bear in mind that the same sensor is used in many models a manufacturer uses & their locations may vary.
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07-02-2004, 06:32 PM
#8
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BoSoxFan:
Just got home from work. Temp reading during the drive home (Downtown, DC to Alexandria, VA [Landmark area]) was 95 F. That's highway driving at an average of 50 mph (light traffic today) after having been parked underground all day, with a 20 minute commute.
Out of curiosity, what was your reading?
Just got home from work. Temp reading during the drive home (Downtown, DC to Alexandria, VA [Landmark area]) was 95 F. That's highway driving at an average of 50 mph (light traffic today) after having been parked underground all day, with a 20 minute commute.
Out of curiosity, what was your reading?
07-02-2004, 06:37 PM
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2004 E500
Haven't left the office yet but getting ready to leave now. I'll let you know when I get home. I'm driving my Porsche today but the results should be similar.
