OK, interesting topic, I have to admit. I don't check my coolant ... not in the last 30 years. Why you ask? Well ... simple. I absolutely hate working on engines and gasoline motors. And I do believe in servicing on schedule. So I take mine to my brand dealer for oil changes and general maintenance. Yea, it may cost a little, but I never have worries this way.
I just had an oil change, oil filter, fuel filter, Deferential flush, Transmission flush, all fluids checked, and even batteries tested on my Dually (just last week) ... at the tune of ... well ... expensive! Yea it costs. But ... I don't have any worries this way!
I am forced to add my own DEF .... which I hate doing, but I do it! Anything else... well ... face it ... that engine has so much stuff and so much electronics on it ... I look under the hood and just shake my head! And then I realize why it cost me $54,000 for that beast!