90:10 isn't enough glycol to raise the boiling point much. If the boiling point is a concern you should be running 100% antifreeze. 10% water boils at 215C instead of the normal 212. 100% glycol boils at 320F. A more likely cause is your radiator pressure cap isn't holding pressure. Have it pressure tested. A normal cooling system is under pressure and boils at about 240F.

Most cooling systems only require a 50 50 mix. 10% water wouldn't take long to evaporate.

that is to high of a concentration. if you been doing that for a long time then it probably has eaten away at some of the gasket and your losing it that way. there is a reason why it tells you to use a 50/50 mix.

that is to high of a concentration.10% water wouldn't take long to evaporate.

pull back the carpet on the passenger floorboard. look for a trace of coolant running down the firewall.

also all coolant systems in working order have a balance point. topping off with coolant will just push out the extra coolant when warm.

hi. im curious why im losing water/coolant in reservoir, i live in a tropical area, sometimes its sunny sometimes its rainy, but no winter. So its impossible to freeze the water in the radiator, but i still put coolant but just about 10%, just to increase boiling point and avoid corrosion.

question: am i losing coolant because of evaporation ? and if yes, is it because of the 90:10 ratio ?

i know if you put 50:50 you should not lose coolant/water.

no leaks, and no white smoke and not overheating means its not the gasket. '91 galant manual trans.