Pontiac Repair: Temperature Gauge Reading Low, manifold gaskets, pontiac montana

Question
I have a 2002 Pontiac Montana mini-van with a V6 engine. The engine temperature gauge shows that the engine runs at about 140 degrees. The gauge reads from 100 to 260 and it consistently runs at at the 1/4 mark on the gauge. The heater will not blow hot air either. It does get warm enough to get the chill out of the cabin but it does not get so  hot that we want to turn the heater temperature down. Any idea on what the problem might be? A faulty or stuck thermostat?

Answer
Hi Sam:

first off check to make sure the cooling system is full of coolant check it when the van is cold. If it's low top it off with a 50-50 mix of dex-cool coolant and water only. Chances are if it's low the lower intake manifold gaskets are leaking or maybe even a head gasket. If not and the system is full then I would suspect a thermostat that is opening too soon. and maybe even a restricted heater core. the heater core would be down the list of ideas. but the other 2 oare very good chances.
good luck :)