car is a 1999.5 a4 with the aeb engine...everything appears to be running fine....in normal driving my temp guage is happily in the middle of the guage at 12 o'clock and i have no issues at all.

if i drive at 150km+ for a few minutes my temperature guage drops all the way down to 9 o'clock and i have no heat at all. what is causing this?

if i slow back down to legal limits i have heat again very quickly

do i need a new temp sensor? or thermostat?

New radar and laser speed enforcment devices use heat signature to calculate speed. Once you past legal speeds, your car goes to stealth mode!!!

Seriously I have no idea. Sorry could not resist.