@pioneeraron : I think engine oil is OK. Just check whether there is any visible leak (yet very small). May be you can keep a white thin paper or the brown paper that use for covering books. Keep it below your car and start it and see if there is any spot. Also you can repeat it after a drive (the idea is to check at different driving conditions. If we are sure that there is no visible leak then it can be due to evaporation through hair cracks on container or hose or through the loose cap. If there is a leak why it stops at the minimum level (as mentioned in your post)? It can be due to change in pressure inside the can due to some kind of tiny cracks. Also check whether your fan is working properly. I don't have much idea about the internal leakage. Here is a link I found about coolant leak. http://www.aa1car.com/library/coolant_leaks.htm Any way keep a bottle of water coolant mix in your car so that you can use it for emergency.