Outdoor temperature display
 

My Outdoor temperature display is rarely ever right and normally 10 to 15° off. I park my car in my air-conditioned garage and when we left this morning the temperature showed about 75°. After being out and about grabbing some food and doing a little shopping with the wife I returned home and the temperature showed 86° wow the true outdoor air temperature was 93°. The car sit in the parking lot for 30 minutes and then I sit in the car with it idling for another 10 minutes waiting on my wife. I would think that would be plenty of time for it to display the correct temperature or even hotter since I was idling.

Most cars use a thermistor and it's located pretty close to the road surface. As you know heat rises, and if the road surface has been baking under the sun, plus whatever type of road it is, the readings can be off as high as yours. I personally have Android Auto running all the time and the difference in temps is usually about 5-8F between the two. Some days they do match up, or are within 1-2F. I just never rely on the temp that the car is reading.

Honestly, these don’t seem to any more or less reliable than other cars I’ve had, Lexus, Mercedes or Cadillac. . Sitting in traffic they always seem to read too high, other times spot on and others still oddly low. I just use them as a general guide anymore. I guess it’s hard to place the sensor somewhere that isn’t too affected by the environment the cars operate in.

while I agree with you they are not normally very reliable they normally will read higher than the outdoor temperature by a few degrees. My issue is that it only went up from 75 to 86° in about an hour and a half of being outside in my garage. The thing seems to adjust so slow but it never makes it up to the actual temperature outside.

Something isn't right. Maybe you sensor is defective? Mine usually corrects within a few minutes of driving. 10-15 degrees off is huge.

In hot weather my outdoor temperature reading is consistently 5 to 12 degrees too low. I just assumed it was inherently unreliable in all Lexus vehicles, much like the ridiculous navigation. For the latter the dealer tech guru laughed and recommended google maps, and for accurate temps I simply glance at my Apple Watch which is always correct.

The Apple Watch is not measuring the temperature, just reporting it from a source, so not an apt comparison. As for the navigation, yes, like most internal memory system over a spectrum of brands, these can be poor at times, though I've experienced some of the horror stories you read about. The new ones, like in my 22 ES, are tied to Google maps and not reliant on internals.

I have noticed the ambient air temperature sensor on my 2019 is very slow to adjust to outdoor temps, and even after some time, typically lower than actual. With that in mind, I don't think what you are experiencing is correct, but I also don't think it is all that unusual with this model. Oddly enough, our 2016 NX and now 2021 RX both seemed to adjust more quickly and the resulting temp after some time outside seems to more closely represent my other temp sources. You would expect the manufacturer to use the same sensor in all of their models, but this suggests that the ES may have a different sensor than their SUVs?

Perhaps with the shortage of chips and the like, they are using what they can get their hands on.

Mine is ridiculously slow. I can be driving 20-30 minutes after going from a cool garage to a warm day and still not have it adjust. My last car (not a Lexus) was bad in this respect, and I guessed it was programmed to be slow in reacting so it didn't overreact to momentary changes in conditions, but this one is even slower.

yes this is exactly what mine does because my garage is air-conditioned there’s often a 20° to 30° difference in temperature inside the garage versus outside. So when it’s 95 outside and 75° in the garage I can drive the car for an hour and it will never make it all the way to 95°.

My garage isn't air-conditioned so that maybe a contributing factor. Perhaps all cold air in the garage over-night act as cold blanket so it insulates the sensor and as the result it takes longer to adjust to outside temperature. As a test, leave your vehicle outside for a few hours before you go for that drive.

Even when you are stopped on asphalt for a period of time?
This is when I usually see a higher reading than ambient temp when its hot outside.
Once driving the air passing over the sensor does cool it off quite a bit.

ES 350 Temperature Sensors
 

Couple of TIS diagrams with Temp Sensor locations. An additional sensor is located inside
the cabin, look just below the Start/Stop button and see a postage stamp sized slotted opening.
While HVAC vents obviously blow air into the cabin, this little guy draws air from the cabin to
determine the inside temperature. Be sure to not attach any phone mounts, St. Christopher medals
or other obstruction over this seemingly minor device.

Pretty funny all those sensors and the outside display is still never accurate. I've never owned a car that had an accurate outside temp reading especially in the warmer months. This one is no different.