On a Golf GTI whose 'computer' dashboard display has failed, I have kludged a temperature solution with one of those external/internal wireless 'weather stations' that Aldi and Lidl sell.
I wrapped the external sensor in duct tape, including wire for attachment. It is now attached to an air intake just below the bumper.
It reads about two or three degrees high on a very sunny day --- I assume because the air near the road is warmer than ambient; I think it's protected from heat radiated from the road; it certainly is from direct sunlight. It reads quite high some time after I've stopped --- I guess warm air from the radiator or oil cooler.
Otherwise it performs as required (for about two years now); the sensor signals seem to have no difficulty getting inside the car. However, long wave signals for the radio controlled clock are not received inside
Best regards,
Jon C.