Help Quick!!! Fan
Sounds like you didn't bleed the cooling system and have air in it.
If you have air where the dash temt sensor is, there will be no dash reading. You have to loosen the tall rod near the t-stat while you fill the coolant until it starts to come out of the base. Take it to a rad shop and have them check it if you're still not sure. 3 things will kill your engine headgaskets: 1 over heating, 2 high exhaust back pressure, 3 detonation. Good luck