Power loss, valves ticking, feels heavy to run then stop with a boiling reserv tank..

[Cheromaniac]

If you're not losing coolant and the level inside the overflow reservoir isn't going down, it's just possible that your radiator cap isn't holding pressure and is allowing the coolant to boil. It's a simple cheap fix to replace it and see if it cures the problem.
Also remove the overflow reservoir and rinse it out thoroughly. Sediments can build up at the bottom and prevent coolant being sucked back into the radiator when the engine's cooling down.