Or go to an emissions shop and have the radiator sniffed for free.If the above yields no answer theirs always the usual checks when it comes to lose of coolant;
- start with drips under car ( cardboard can expedite that process)
- check hoses/connections (including back to the firewall)
- Check radiator/ heater core and Radiator cap
-check exhaust (thick white indicates bad head gasket, can be tricky with cold ambient temps)
-check oil (if the dipstick shows traces of coolant or oil is milky, indicates bad head gasket)
((If head gasket is suspected try the chemical leak test for the radiator, most parts stock them))
It boiled the coolant? You may be running an improper mix / to much water, coolant should never boil especially under normal driving and such.It got hot enough to boil out the fluid, so I can't really check for drips right now. I changed oil 1400 miles ago and when it got hot it the oil monitor said 0%. I changed the oil and it looked ok no milk at all. It also has an oil leak somewhere on the front of the motor. To much in the way to see anything. I pulled the plugs and stuck the bore scope in and they all looked about the same.I'll do the card board trick after it cleans up. Where does the reservoir vent at?