Thermostat trouble? Barely reaches 90 C in the winter (Norway) '95 TDK @175000

[$hitblast]

Temperature seems to rise normally up to 75-80 C (outside temp -3 C) over a 5-6 min span of driving; then slowly drops down to 65-70 C and stays there for the rest of the trip. Drops further downhill. Once got it briefly up to 90 C while climbing some 1000 meters up the side of a mountain.

I guess this is the thermostat acting up?

[h100vw]

Temperature seems to rise normally up to 75-80 C (outside temp -3 C) over a 5-6 min span of driving; then slowly drops down to 65-70 C and stays there for the rest of the trip. Drops further downhill. Once got it briefly up to 90 C while climbing some 1000 meters up the side of a mountain.

I guess this is the thermostat acting up?

yeah, could be stuck open.