Temperature gauge dramatically spiking when turning left

I have a 1997 Subaru outback.

Due to corona / loss of job / personal sickness / family illness I do
not have much disposable income to pay for this to be fixed unless
absolutely necessary.

I have had issue with the coolant reservoir emptying quickly but I
have not been able to narrow down a leak.

Yesterday when idling I notice the A/C was ambient temperature,
then it suddenly kicked in and was quite cool. At this stage I noticed
the car was getting warm and I made a move home to cool it down.

But this didn't work. Every time I made a left turn the temperature
gauge would spike. Just left. Not right.

I let the car cool and took it her a run around 4am when it was
cooler. Same thing, it warmed up to normal (just below midway
point) within about 2km of leaving home. Was perfectly fine until I
took a left turn and then the gauge spiked. This continued to
happen for every left turn. While going right or straight had no direct
effect but I did notice the temperature would slowly decrease as
would be expected. Coolant and oil levels were at optimum before I
left.

I'm wondering if I have an airpocket as something is obviously
happening with the reservoir. Or a blockage? Or could there be an
issue with the temperature sensor - but I did not think it would be
this as the problem is consistent. Same with a faulty thermostat -
the error only started yesterday but the temp gauge in the car
always responds normally and always stabilises around midpoint.

Please help. Thanks