Car hasn't been driven for about a month (05 wrx, 119k), but after a couple of drives this week (using the heater) the engine started overheating. Pulled in to my drive way yesterday and there was a bit of smoke, so let it cool overnight.

Checked it out today in the light and noticed the coolant reservoir was low. I have added some coolant + demineralised water. Just let it idle for a while and seemed fine, but after some low revving temps were rising pretty quickly. It doesn't look like the coolant is being circulated from reservoir.

My question is how can I probably distinguish whether or not the coolant is being circulated properly? If not, can I simply add coolant to the radiator or engine (tabbed cap)?

Service is booked for Monday so this will help me determine if I can drive there or should simply get a tow.

Many thanks