[mikefaster]

Feel one heater hose and see if it's hot and then see if the other is cold... If that's the case, then the heater core is clogged... I have fixed this numerous times by swapping the heater hoses (they are the same size)... You will usually have heat instantly, if not better heat after running it for a day... There is usually enough hose to swap them and you can leave them swapped... If the weather was warmer, you can put a garden hose on reverse flow and that will usually free it up as well...

If both hoses are cold, then you may have a head gasket seeping, causing pressure build up of carbon monoxide in your cooling system... The gas rises and doesn't allow water to travel up that high... You can try a 7lb radiator cap then...

Sometimes, people just don't properly "bleed" the system when they change the thermostat... Meaning, you may have just needed a thermostat, but you didn't run it long enough without the cap off while viewing/filling the water level... Many people will change thermostats in very cold weather and it seems like the engine "never warms up enough"... The trick is to KEEP running the engine until the fan comes on at least once, without the cap on... If the water wants to keep coming out during this process, you may have a head gasket seeping...

Did it recently overheat or have a cooling system problem???

Mike