When to top off coolant?

I check the fluids on my 2012 prius pretty often. Noticed recently it’s just slightly below the “Low” when a month ago it was perfectly at full. The distance between full and low is so minimal, how important is it to get a gallon to fill up to the full mark. Hoping I’m not loosing any coolant in the cylinders. I will usually have a rough start just once a year on the coldest day of winter morning. It happened a few weeks ago after letting my car sit for two full weeks without starting it. Hasn’t happened since. I swear I freak myself out every year thinking it’s the head gasket but I guess it’s just the moisture built up in the intake. I never short trip and don’t turn it off while it’s running.

 

Also last coolant change was at 155k and I’m at 205k now. I drive about 20-25k miles a year, worth to just go ahead and do a drain and fill?

 

Cleaned full circuit at 140k with the updated intake manifold and new egr valve. I’ve been doing 5k oil changes since 120k. I only burn .5-1 quart per 5,000 miles. I’ll plan on doing a full coolant service. Trying to keep this car as long as possible while I rebuild my 1913 money pit house.

 

It’s my daily driver to work. I drive a 40 mile round trip M-F. Majority interstate miles going 70-80 mph on average. This Prius has barely had a day off since I bought it in 2015 with 30k ish miles. Definitely got my moneys worth out of her. Original battery still going strong, 45 mpg on average.

 

My 2004 Chevy Silverado is the one that does the sitting lol.