Grand Am Coolant Leak Help.

I have a 2004 pontiac grand am with the 6 cylinder engine. The temperature gauge on the dash had been reading high. I checked the coolant levels, it seemed a little low so I added coolant. The next day the temperature gauge went into the red and when I opened the hood I could hear a leak but couldn't find it. I rented the coolant system pressure tester and found a leak that looked like it was coming from the thermostat housing. When i got to it, the thermostat gasket (or whatever it is called) looked all mangled up. I replaced the thermostat and the gasket, and put it all back together, and pressure tested the system again. and it still looked like it was leaking from the same spot, but when I looked closer I could see that the leak was actually coming from what looks like a kind of flat silver colored cap located on the engine right behind the thermostat housing. ( I'm not too familiar with all of the terminiology so sorry). But does any one know what that cap is called and what I need to do if it is leaking. It is silver colored about 2 inches in diameter. Thank you for any help.

Sounds like you might be describing a core plug. Any way you could snap a picture to make sure?

Also common leak spots on this motor include the lower intake gaskets.

A picture would be your best bet if you want us to help diagnose a leak.

What you are describing sounds like the '"Dummy" distributor shaft that drives the oil pump...if it is you will see the old style distributor hold down clamp on it......when it leaks, it leaks oil, not coolant......the lower intake gaskets are known for leaking , and what you may be seeing is the coolant puddling on the cap and also in the depression in the top of the block, when the lower intake leaks.....also did you clean all the coolant from the top of the engine when you changed the thermostat?

By the way, if the coolant system isn't filled and properly bled, you can create an air pocket that may cause an overheating problem and your gage to read high.....