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

Did you check the header tank? Was it low?

Where was the smoke coming from?
Did it smell like burning coolant?
Are the thermo fans turning on?

Do a good thorough check of any coolant leaks as the coolant has obviously gone somewhere which will probably mean you now have air in the system. You will most likely have to bleed the coolant system of any air. Do not drive the car at all if you see the needle rise past normal.

ditto, burp the cooling system, there is an airlock somewhere.

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Long live the WRC