Apologies for yet another thermostat thread (been searching forum trying to find a similar situation with no luck)
Have a Vectra 1.9CDTi 120 and it had the standard issue of not heating up when driven at speed (was heating eventually when crawling around town).
Being that i've only had the car a couple weeks the garage that sold it took it in and replaced the thermostat, now it seemingly heats up better but the temp gauge still drops right back to the bottom on longer runs/higher speeds.
The actual heating is perfectly fine and on full heat the interior is insanely warm therefore the garage thinks theres nothing to worry about.
However, on looking through most of the temperature related threads on here everyone seems to talk as if the guage should go between 80 and 90 and stay there no matter the distance/speed.
Thoughts and/or reassurances would be welcome