You may have several things going on.
First, look behind the passenger tire on the firewall where the heater hoses go into the dash. You should see a valve with a vacuum line on it. This valve is right in the heater hose. It could be stuck, or the prior owner might have cut it out because it was leaking.
Or, they may have looped the heater hoses with a bypass as the heater core or the valve was leaking.
Also, it may have a 160 thermostat in the engine. If so, it will take some time for it to heat up enough to really feel, even if the gauge says 180.
Most of the time you will find the heater has been bypassed, or the heater control valve is sticking or the vacuum hose has come off.