2008 Volvo C30 Coolant "leak" expansion tank

[Pretribrapper]

I seem to have a coolant leak right under the expansion tank. At first I thought it was a cracked expansion tank but now it appears to properly be coming out the relief valve in the top of the cap down the rear outlet of the tank. Seems to be quite a bit of coolant but when I relieve pressure in the cap coolant level resets to max. Is there something that would cause the unnecessary pressure in the coolant expansion tank that it would be forcing out more coolant than normal? Would it be the thermostat or something else?
The car runs and drives fine and temp level stays right at half. Any ideas?

[MoVolvos]

I seem to have a coolant leak right under the expansion tank. At first I thought it was a cracked expansion tank but now it appears to properly be coming out the relief valve in the top of the cap down the rear outlet of the tank. Seems to be quite a bit of coolant but when I relieve pressure in the cap coolant level resets to max. Is there something that would cause the unnecessary pressure in the coolant expansion tank that it would be forcing out more coolant than normal? Would it be the thermostat or something else?
The car runs and drives fine and temp level stays right at half. Any ideas?

PV=nRT. If your system is not completely sealed pressure won't build which in turn boils the coolant besides leaking out. Don't use the level as an indicator of what the system is doing in this case. Either pressure test the system or get a HC tester to see if the head gasket is causing the problem.

Most places rent for free but you need to purchase the fluid.
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https://www.oreillyauto.com/detail/c/li ... lis0/75500
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[Pretribrapper]

Thank you. Turns out combustion gas is getting into coolant. Really not news I wanted so I am attempting to do repair job myself. Good video on You tube. Local shop by me will resurface head for $100. Anyone know good place to get the Volvo Expansion pliers for less than $100??
Pray for me!