Outside Air Temperature Discrepancy

[pottslaw]

We've got an MME RWD ER (Infinite Blue) that drives and handles well, but as the temperatures here in Phoenix have started to climb, the outside air temperature shown on the display reads high by 13 to 16 degrees. I assume the car is using the outside air temperature to manage the batteries and the vehicle performance. Has anyone else seen this type of error? Is it harmful to the car (especially the batteries)?

For example here are photos from this afternoon. Weather.com reported the temperature at 113 degrees, while the MME displayed 129 degrees.

Thoughts?

Thanks!

Rick

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[jsteach]

Hi Rick, most if not all the sensors are mounted under the front bumper and are meant to read road temperature, especially design to check for black ice. Unseen ice in the road.
If road temp gets under 34 degrees a warning light of sorts will flash or come on. Not sure
with the MME. Will have to look it up.

 

[breeves002]

I have an issue with the sensor too. The sensor on my truck and cayman is fairly accurate and makes sense, but the mach E is always wayyyyy off. I don't really understand it. It is always significantly higher than outdoor temp while my other vehicles are generally pretty close, or slighly higher (a few degrees).

I'm not exactly sure how a thermistor checks for black ice @jsteach but maybe you can explain it.

 

[The Electric Duo]

Official temps in weather apps are done very specifically - 6 feet above the ground, in the shade, in a well ventilated area. That's great for consistency, but you want the Mach-E to accurately measure the temperature that is affecting its performance (battery). If the car is sitting in a sunny parking lot, even if the sensor is shaded, it should be higher than the "official" temp.

I can even see a difference in tire pressure if I park with one side in full sun.

 

[macchiaz-o]

This is only my third vehicle that has some sort of temperature display. On the previous two, when I started the car after a hot day of sitting in an unshaded parking lot, the gauge would read high.

On the Mach-E, it reads really low in this case... Because it's apparently showing me the outdoor temp that it held from when I'd park the car that morning. I have to drive for a few minutes in order to observe the reading move upwards and settle into its new position.

BTW the 129 reading doesn't surprise me right now. ? ? It may actually be that hot at whereever the sensor is located. Surfaces can be hotter than air, especially when within the greenhouse of a vehicle.

 

[pottslaw]

Official temps in weather apps are done very specifically - 6 feet above the ground, in the shade, in a well ventilated area. That's great for consistency, but you want the Mach-E to accurately measure the temperature that is affecting its performance (battery). If the car is sitting in a sunny parking lot, even if the sensor is shaded, it should be higher than the "official" temp.

I can even see a difference in tire pressure if I park with one side in full sun.

I see your point, but a 16 degree discrepancy while traveling 40 mph is light traffic is a concern. Side by side with our 2018 Ford Edge, the Mach E is consistently reporting 13 to 16 degrees higher under the same conditions. It is warm here in Phoenix, but it certainly isn't 129 degrees!

Additional data: With the car parked in the shade in the garage, the Mach E reports 119 degrees. The temperature in the shade in the garage is actually 106 degrees. The variance in temperatures isn't necessarily correlated to driving conditions.

Thanks!

 

[pottslaw]

This is only my third vehicle that has some sort of temperature display. On the previous two, when I started the car after a hot day of sitting in an unshaded parking lot, the gauge would read high.

On the Mach-E, it reads really low in this case... Because it's apparently showing me the outdoor temp that it held from when I'd park the car that morning. I have to drive for a few minutes in order to observe the reading move upwards and settle into its new position.

BTW the 129 reading doesn't surprise me right now. ? ? It may actually be that hot at whereever the sensor is located. Surfaces can be hotter than air, especially when within the greenhouse of a vehicle.

Thanks for the reply. You and I are driving in the same conditions here in the valley. Have you seen 129 degrees displayed in yours? If it is normal I am not going to worry about it, but it does seem odd.

Thanks.

 

[jsteach]

I have an issue with the sensor too. The sensor on my truck and cayman is fairly accurate and makes sense, but the mach E is always wayyyyy off. I don't really understand it. It is always significantly higher than outdoor temp while my other vehicles are generally pretty close, or slighly higher (a few degrees).

I'm not exactly sure how a thermistor checks for black ice @jsteach but maybe you can explain it.

Most are calibrated for lower accurate temperatures. Road surfaces can be between 30 to 60 degrees hotter that outside air temps depending on surface material and depth of material . Most ground surfaces like dirt is 8-15 degrees hotter and sand a little more.

 

[macchiaz-o]

Additional data: With the car parked in the shade in the garage, the Mach E reports 119 degrees. The temperature in the shade in the garage is actually 106 degrees. The variance in temperatures isn't necessarily correlated to driving conditions.

I don't think the car will update its readings while it's parked in your garage. Let's assume that the sensor is collocated with the sunload sensor (the small protrusion you can see from your driver's seat if you look towards the bottom-center of the windshield).

If you can place a thermometer in that location and drive around outside for 5 minutes at at least 20 mph, I'm guessing you'll find the two readings to be somewhat consistent.

When you pull into the garage, the vehicle speed is below 20 mph and based on what someone posted here (in a different discussion), the vehicle will stop averaging in new outside temperature data samples because it's considered too inaccurate in their design.

 

[macchiaz-o]

Thanks for the reply. You and I are driving in the same conditions here in the valley. Have you seen 129 degrees displayed in yours? If it is normal I am not going to worry about it, but it does seem odd.

Thanks.

I park outside, unshaded at work all day and it should be quite hot this week. I'll try to remember to check.

This is from inside my garage on June 5. It was probably 105 or so in the garage at that time, but like I said, I think this 120 reading is from while I was driving home.

 

[breeves002]

In reading the WSM it says that it can take up to 5 minutes after starting the car to get the raw value from the sensor. The HVAC module filters the data.

 

[SnBGC]

To add what has already been said.....
There are sensors in the battery pack and those readings are what really matter. However, the vehicle needs to know the air temp at the louver openings so it can accurately determine the effectiveness of the cooling system. Or more accurately, how much cooling can it expect from just using the radiator to transfer the heat from the coolant. If ambient it too high, then the chiller gets involved. When the screen says 120 degrees, that is the temp about 8" above the roadway which is where the air is collected.

Ford could've put another temp sensor under one of the side view mirrors to show us a more reasonable reading while driving. In the end, it comes down to cost and weight savings for something that really isn't totally necessary.

I have measured surface temps in my driveway near the garage door of 129 degrees so it gets pretty darn hot here. ?

 

[SnBGC]

Here is where I park at the office.
Crazy hot!

 

[SnBGC]

The ambient temp sensor must be influenced by the heat under the hood. It said 127 in my driveway but that is in the shade when I get home so there is no way that is accurate. I got out my IR temp meter and measured 104 degrees at the closed louvers. Measured the pony emblem and it was 117 degrees. Started the car to open the louvers and pop the hood and measured 117 at the radiator (portion exposed through the louvers) and 132 degrees in the front compartment area. No way any ice is going to last very long in there so the shrimp feast is going to have to wait until the fall.

Lastly. Range impact at these extreme temps is 20%. My normal range is 300 miles if the temperature is 105 or less. 115 degrees or more and range drops to around 240 miles looks like...

 

[ARK]

This is only my third vehicle that has some sort of temperature display. On the previous two, when I started the car after a hot day of sitting in an unshaded parking lot, the gauge would read high.

On the Mach-E, it reads really low in this case... Because it's apparently showing me the outdoor temp that it held from when I'd park the car that morning. I have to drive for a few minutes in order to observe the reading move upwards and settle into its new position.

BTW the 129 reading doesn't surprise me right now. ? ? It may actually be that hot at whereever the sensor is located. Surfaces can be hotter than air, especially when within the greenhouse of a vehicle.

This has been my experience too. It seems the temperature sensor updates relatively slowly.

I think it is very common to get an off-the-chart high reading in any car if you have parked in the sun when you first turn it on, but OP noted in one of his posts that it seems to last while he is driving.

For me, however, the temperature corrects itself after a few minutes of driving. For example, when I drove my Mach-E on Sunday at midday, it was in the high 80s/low 90s in Los Angeles, but I distinctly remember that the Mach-E was showing only 67 degrees. It stayed at 67 degrees until I was driving for a minute or so and was about a mile from my house when it started to jump up by several degrees ever couple of seconds before it stabilized in the high 80s.

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