Oldsmobile/Buick Repair: heat loss in Alero, coolant loss, coolant level

Question
Hello.  Here is the vehicle info:  2000 Alero with 3400 v6, 78k miles.  My problem is that I have noticed this winter that the car has been having a hard time blowing enough warm air into the interior of the vehicle to keep it warm.  The blower and all vents are working fine, the vehicle temp is up to about 1/3 - 1/2 when looking at the guage.  Today for example was -20 this morning and I let the car run for about 15 mins before leaving on my 35 mile commute to work.  I expected that it would take a lot to keep it warm in there going 60mph to work, but I had the fan on high and on defrost/floor and all 3 of us in the car were cold by the time we got to work.  Living in northern MN I know to expect that it may take a little more keep the car warm in those temps, but it seems like for the last few weeks it has been a real pain to keep it warm and has been getting worse even when above zero out.  One of the guys I car pool with suggested it may be the thermostat staying open.  Do you have any thoughts/suggestions?  Thank you.

Answer
Hi
1)
I would frst check coolant level in the radiator/overflow surge tank.
Make sure it's full and topped off. Low coolant, I find, is the most common cause of lost heat.
If the coolant is low, then I would HIGHLY recommend taking it to a repair shop and having the cooling system pressure tested and the cause of the coolant loss found and repaired.
2)
If the coolant level is full and correct, then I would suspect the thermostat OR coolant system blockage somewhere.
I Hope this helps
Good luck and STAY WARM!
Pawl