| Well, that depends what is wrong.
Check the reservoir, is it low or have had to add fluid? If you are losing fluid, then it is usually one of three places.
1.The easiest is the tubing between the block and the radiator, check that, make sure there is no cracks and check to see if the tubes are leaking at the ends. Best if you do this while the car is either running and warm just got turned off, this way the fluid is flowing and you can see it leak.
2. The radiator it's self can start leaking, this is kind of hard find, but the easy way is to put some plastic under your car when you get home, let it sit over night on top of the plastic, and check to see if any antifreeze is on the plastic.
3. This is the worst case, check this one first, antifreeze could be heading into the engine. Check your oil, if anti freeze has gotten into it, it will turn a dark whitish color. another easy way to tell is to stand behind your car when it is running, if there is white stuff and it smells kind of sweet. If this is the case you probably are looking at a new head gasket. Do NOT run your car in this condition. Anti freeze explodes much more violently than gas and can easily crack your heads, it also kills bearing and can easily seize an engine in minutes.
As for your burn marks, where exactly are you looking for burn marks? I usually wait to change my radiator until I can easily tell fluid is coming out, see number 2, or once I actually heard it explode inside the car. | 
When is it Time to change Radiator? 
than that's when its dying? If you have to change it out, should you replace with OEM or something betta. I am a daily driver/performance, not strickly performance.
