temp gauge too low

I did a intake gasket replacement and now I keep running into different problems. now the temp gauge on the dash will stay too low. I am just using this gauge as a reference. The blazer at start up will be fine, when about the time you would think the thermostat would open it is not and the car wants to start to stall out. It isn't until I got out and relieve the pressure at the radiator cap that it will start to register on the dash. I know this is a pressurized closed system, but have never encountered that that temp on the dash will remain too low. I guess I will try to flush the whole cooling system as I only did the radiator and heater core. I am just confused to the low temp reading. Any suggestions would be appreciated
 

Did you replace the thermastat when you did the gasket replacement?? Seems to me that you might have a faulty thermastat!!

Even if he did replace the tstat with the gasket....it's definitely toast now either way.  It's stuck open, causing the coolant to circulate all the time, keeping it engine temps real low.

So x2 on the t-stat!

Might be a big air pocket in there since you had the intake manifold off. A good backflush using a flush kit "T" in the heater hose is a good way to bleed air out of the system.

i think for low temp I'd have to go with garry on this one... I think its an air pocket... if its trapped aroudn the t-stat.. the steam (air pocket+heat=steam) wont be enough to open the t-stat which would keep your coolant from circulating causing the low temp reading...  which is why when you bleed the air out..i.e. opening the cap.. the temp reading corrects it self.. the hot coolant hits the t stat.... opens and circulates as normal...... jsut my 2 cents