Is it safe enough to open coolant reservoir when empty

Its never good to open a coolant reservoir when it is hot. You should be ok if the reservoir is empty, wear gloves and crack the cap first don't just take it off. Also a good idea to wear eye protection.

 

The steam is as much a problem as the water is and it’s likely to have steam if it’s low and hot.
A glove and some caution is always a good idea

 

Agreed. Crack the cap to relieve any pressure, then when the pressure is equalized you can remove the cap.

 

Trick I learned many many years ago about radiator caps and pressure. Find a rubber hose connected to it. Preferably one of the bigger ones. Squeeze the hose to see if there's any pressure in the system. If so, DO NOT open the cap. If you can easily squeeze the hose, be careful for the potential for pressure. But, you're probably OK to open it. Typically, it's a screw on cap, Just be slow and if you start to hear any hiss, close it back up.

 

Or leave it open just a tiny bit to let the pressure bleed off. Of course that tends to mess with the coolant level so it's still better to wait until it's cool.

 

Um, why is it empty? Trouble a brewin',,,even those plastic reservoirs have pressure, but I'd see where the coolant is going,,again and again and again, you get the idea, this is another of those questions that's pretty basic, and again, I don't blame this person, but a lack of mechanical knowledge can be dangerous, even deadly. The fact that someone doesn't think a coolant container when hot may or may not be dangerous,,,I know, I know, they asked, but it's still a mechanical machine that requires at least a shred of knowledge. May as well ask in the same question, "where's the nearest Urgent Care?