temperature reads inaccurately

[ANGELO33]

hi guys i have passat 1.8turbo 1997 AEB engine my problem is temperature reads inaccurately what i mean is it doesnt stays at the normal temperature when im driving through cities the temp goes 75 celsius then goes down to 50 celsius even though im running more than an hour.when i try running in motorway temp suddenly drop slowly from 75 to 45 celsius and stays there no matter how long your journey is. add for my pain is i cant use the chip to trigger coz it depends on the temp of the engine at least the engine temp will be 65 celsius above bcoz of this my chipped is useless.
is it the thermostat? coz ive change the coolant temp sensor so many times with 2 OEM and 1 original sensors.

[onzarob]

are you sure that the engine is reading erratically as the gauge is controlled by one half and the ecu uses the other of the sensor.

I think you need to use Vag-com to log readings.

[ANGELO33]

yes couple of weeks this what i have evrytime i renew my sensor
16500 (P0116) Engine Coolant Temperature Circuit Range/Performance
INTERMITTENT