I have a 2009 C70 and I have an issue with it running hot. Here is my story.
It started with the rear heater hose connectors(plastic) at the rear of the engine bay. They were brittle and broke causing leak. Repaired both. Thought that fixed it, but drive about 30 miles then got another leak. Found problem to be the lower radiator hose(octopus hose)fitting broke also due to brittleness. Replaced that. Thought that was the problem. But now it runs fine for about 30 miles or so then it starts running ho and the temp gauge needle moves up toward red. Stop let it cool for a bit then can go about another 30 mile then it happens again.Now coolant is soaking the drivers side wheel well, tire. I think I narrowed the leak down to under or near the coolant recovery tank. The fluid is showing on the low mark . However, when I open the cap, pressure is relieved fairly violently and the water level fills up the recovery tank to the cap and starts pouring out. Anybody ever have this issue or have any ideas ? I AM THINKING IT MAY BE A THERMOSTAT ISSUE.. like it is not opening and allowing water to flow through the system and radiator. Like it should.
Thank you !
Mike

 

Commonly when an engine is overheated a couple of times - combustion gasses leak into the cooling system from a damaged head gasket. The combustion gasses stop the normal flow of coolant in the system. (due to the addition of pressurized gasses into the coolant in funny places)

A good test for that is to use a combustion leak detector - It samples the air in the cooling system (in the reservoir) and if combustion gasses are present - the fluid changes color. You may be able to rent or borrow a tester from a local auto parts store - or they don't cost that much.