So when i drive i notice my engine gets a little hotter than it should sometimes and when i pull home i can hear the radiator cap 'bubbling' like pressure is escaping or something and when it cools down i check the coolant level and the radiator is like half empty and the overflow tank is full. so i put coolant from the tank into the radiator and when i check the next time, its all back into the tank again and the radiator is left half empty... why is this?

 

What's the psi rating on the radiator cap? It will be stamped or labeled on top. The coolant should get sucked back into the radiator as the system cools, but filling the reservoir is a bit much. Could be your radiator cap is bad and releasing too soon, or you're using too low of a psi rating, both of which would contribute to the engine running hotter.

 

It's rated for 16psi, is that enough?

 

I have an aluminum radiator, with a racing cap rated at 22-24 psi. I don't have a reservoir, and it never burps out. A higher rated cap raises the boiling point of your coolant, which lessens the chance of overheating. But you need to be sure you have a good strong cooling system, as that will put more stress on your hoses, radiator, and heater core. My stuff is good, and have no heater core/hoses, so I'm not concerned with the pressure rating, and I've never had an issue.
Is the coolant that's spilling into the reservoir staying clean, no oily looking residue or anything like that? One concern is the possibility of a bad head gasket blowing into a water jacket, and causing excess pressure in the cooling system.

 

Are you constantly checking the coolant after stopping? You should be allowing the engine and system to cool down so it can suck that coolant ffrom the reservoir back into the system. If it doesn't suck it back, then you've got a problem.
I run 16 lb. caps on all three of my old rigs and don't have any issues with coolant expanding and releasing through the cap. Do you have a temp gauge to tell you what temperature you're running? Maybe it's just running too hot and working normally to release the pressure.

 

I have a temp gauge and it would read from 190 (fine). To 230 (not so fine). When I check the coolant its when it sits over night so it has plenty of time to do whatever it needs. I I'm positive its not the block or head leaking or anything like that.

 

Then check to make sure the hose from the radiator to reservoir is fit on good and tight on both ends.
If it's allowed to suck air when the radiator cap wants to let the coolant flow back, it won't siphon it out of the reservoir.

 

I just put some new claps on the hose so will see where that gets me

 

So it turns out it was the radiator cap. i blew into the hose into the tank and it bubbled and such and then i did it into the radiator and air was leaking for the the cap. just bent the little ledge in more to make it tighter. simple and free fix, the best kind!

 

If it still acts marginal, keep in mind new caps don't cost all that much, and would probably be shinier than the one you have!