My car VW passat 2003 1.8L engine Heats whiles the temperature guarge is at 90f on 2003 Volkswagen Passat

I experience the heating when i drive a long distance like 100 miles or when put on the air condition at even distance of 20 miles whiles The temperature guarge will be at 90F.Some times The temperature guarge will rise to 190F for a while and fall to 90F. Help me.The engine gives a racking noise when the heating starts.

Probably check/or change the coolant sensor, and thermostat. It should be steady around 190deg but if your temp sensor is bad or the gauge is bad, you are probably over heated when it shows 190.
Thank you .However what is the normal position of the temperature guage when in motion ?
Like I stated around 190 deg.
why does the engine give a racking nose even when the temperature is at 90F?
If it was scanned, I would guess the computer would have a code as ' Temperature Below Threshold'. If this is so, then the computer would compensate for the error. That's my opinion without checking it for myself.
I scan it and it shows Code p2181 which says coolant temperature performance is not normal evaporation steam leaks. what should that be?