Difference of temperature of 520 and 530.

 Mine is 5-6degC higher than my old edge 520 and Lab calibrated temp sensor. 

did you find the answer to this discrepancy? I find mine (530 with genuine cover) reads 2-3c higher than 520/510/1030/wahoo element.

that is completely false. Why is the temperature data displayed on the screen? 
So that the cyclist knows at all times if the barometer chip or the electronic board is hot?
Garmin scam when it advertises the devices with functionalities that are a prank

I had noted that my old Edge 510 always read about 6F colder than actual based on riding past the bank sign and assuming the bank display was the accurate reading.  But also based on what the internet would say for my location.  The Edge 530 seems closer to actual.  I did a side by side comparison the other day on a ride and sure enough, the old Edge 510 was showing a temperature about 6F cooler than the Edge 530 for most of the ride.

I have 3 meteorological stations, one of them it is an old Mercury thermometer and my Edge 830 at the beginning when I turn on, shows correct temperature, but after 2 minutes go High 4° Celsius. This is an joke feature. The Grade feature it is also a joke feature because show the Grade of the road about 15 seconds late . And after all this GARMIN SUPPORT don't answer nothing about this. Only "make hard reset". Now I'm waiting the second answer.

I think all this data from such equipments are just for fun. Useless.  Temperature is not accurate 

Yes, my Edge 530 consistently shows about 4 deg C higher than actual, as measured by several other sources (i.e. my car, my old Edge 520, a mercury thermometer: all of which show almost the same reading & it's 4 deg C lower than the Edge 530). Very annoying & no mention of how to troubleshoot this in owner's manual.

Yes, you're right