hi, first post here.
my 740T just recently has really weak heat at stoplights, warmer when driving, and the fan keeps running after we stop the car. i'm wary of adding any coolant to the system even though the overflow res looks low, the last time i did, it turned into a steam explosion under the hood while my wife was driving on the freeway. would adding coolant/water into the res and not the radiator cause that? i used prestone coolant, is that a bad idea? most of my auto repair experience was holding the flashlight while dad or brother fixed things.

and does this site have any online parts/repair manuals so i can look parts up to ask you about them? there is some thing on the drivers side front corner under the hood that has a broken hose, but i don't even know what it does. a black plastic cylinder with 2 long skinny hoses going into the top with a short thicker hose out the bottom attached to nothing. one of the skinny ones on top is broken where it attaches to the cylinder, some sort of vacuum controller?