03 LS not blowing warm air

My mother has an 03 Monte Carlo LS (3.4) and it is not blowing out warm air. She usually starts it in the morning because it's about 10 degress out. It sits and warms up for 20 to 30 minutes with the front windshield defrost on high speed. After 20-30 minutes when she goes to leave for work she gets in and the blower is throwing out cold air still. She recently had the thermostat and cooling system flushed about 2 months ago. I also noticed that when the car is sittin the temperature guage will sit below 210 degrees and it will rise up over halfway and then go down. She had the thermostat replaced before and it fixed that but it's doing it again. But when you drive on the highway (55 mph) it blows out some warm air. Does anyone know what could be wrong? Heater Core? Coolant Leak? Thanks in advance.

My mother has an 03 Monte Carlo LS (3.4) and it is not blowing out warm air. She usually starts it in the morning because it's about 10 degress out. It sits and warms up for 20 to 30 minutes with the front windshield defrost on high speed. After 20-30 minutes when she goes to leave for work she gets in and the blower is throwing out cold air still. She recently had the thermostat and cooling system flushed about 2 months ago. I also noticed that when the car is sittin the temperature guage will sit below 210 degrees and it will rise up over halfway and then go down. She had the thermostat replaced before and it fixed that but it's doing it again. But when you drive on the highway (55 mph) it blows out some warm air. Does anyone know what could be wrong? Heater Core? Coolant Leak? Thanks in advance.

My 02 SS same problem. changed the temp sending unit below thermostat housing. The temp gauge would go about 1/4 up then it quit and the check engine light came on, ran diagonostic check, said to change sensor. I also noticed the electric cooling fan was on from the start..It fixed my problem.

My mother has an 03 Monte Carlo LS (3.4) and it is not blowing out warm air. She usually starts it in the morning because it's about 10 degress out. It sits and warms up for 20 to 30 minutes with the front windshield defrost on high speed. After 20-30 minutes when she goes to leave for work she gets in and the blower is throwing out cold air still. She recently had the thermostat and cooling system flushed about 2 months ago. I also noticed that when the car is sittin the temperature guage will sit below 210 degrees and it will rise up over halfway and then go down. She had the thermostat replaced before and it fixed that but it's doing it again. But when you drive on the highway (55 mph) it blows out some warm air. Does anyone know what could be wrong? Heater Core? Coolant Leak? Thanks in advance.

:banghead: I had the sane problem. Im actually getting it fixed right now. Supposedly my radiator is all plugged up and air some how was getting through a hole which was letting coolant into the engine. Its costing me abour 1150 $$$ to get fixed. so now there taking apart the engine down to the heads and cleaning all the crap that got in there out. Then flushing the coolant and adding new stuff. Mine is an 03 as well.

well i found out my problem. i have to get my intake manifold gasket changed out. it is going to cost a lot as i have read. my coolant was mixing with oil because when i opened radiator cap i looked in and there were brown spots in the coolant so i knew the coolant and oil were mixing. so i expect to pay around 800 to get it fixed. thanks for your suggestions though.