you have a coolant leak somewhere and the sensor inside the reservoir is going low there for you light turns on happened to me turns out my manifold was leaking antifreeze so i had that patched up and replace my cracked reservoir filled it up and bam been good ever since
so how do i pressure test? and what do u mean if the oil is milky? i did the oil change today so explain what u mean..the coolant never goes all the way down it just goes down a little bit and stays that way..
Everything I read prior to my ITM change told me to replace the heater hose that runs in the valley and mine turned out to be a metal tube! Did you replace yours? Mine leaked about 20oz a week for about 2 weeks then it stopped. Think the heater hoses weren't completely seated or something. Fine now. What did you find a tube or hose?
TEST #1: Pressure Tests for the Cooling System The first test of the cooling system is done when the engine is cold. A cooling system pressure tester can be installed in place of the radiator cap. Pressure in the cooling system and hot coolant are not something to be treated lightly. Use caution, and never remove the radiator cap from an engine that has been run even for even a short time. After installing the gauge, pump it up to 10 pounds. Look around for leaks if the gauge shows any pressure loss. Common trouble spots include heads, hoses, water pump and rear heater core. If you smell something sweet when you turn the heater fans on, it may be a coolant leak at one of the heater cores, or simply the O-ring at the rear heater valve leaking. Because there is often more then one leak in the system, it is necessary to continue pressure testing until the system holds pressure. TEST #2 Start the engine cold with no pressure indicated on the gauge. The pressure in the cooling system builds to aprox 7 lbs at normal running temps looking around for leaks. But if the pressure builds quickly to around 15 lbs the pressure is coming from one of the cylinders through the inner head gasket. This can also show up as a coolant pressure loss in the first test. In extreme cases the cylinder can fill with coolant, and will not turn over. This is know as hydraulic lock, and if you suspect this pull the spark plugs and tries to turn the engine again. Pulling the plugs from the engine allows water to escape from the spark plug holes.
About the coolant in the oil appearing milky: Have you ever seen an oil can, or an oil dump pan that got left out in the rain or something? There will be a whitish, milky substance in the oil. It's from the oil mixing with water.
You can find a lot of stuff out on your own using Google.