The Blazer started to over heat today on the way to work. First thing I did was put the heater on full blast and quickly the temp when back to normal rage, but a few miles down the road the heat started blowing cold and the temps started going up until the heater started blowing hot again. This happened all the way to work. Think this is a bad thermostat? Waterpump maybe?

 

Stat or air bubble, possibly the water pump but I doubt it. If it were the pump it would be a regular thing.
Jack up the front PS, block it & remove the rad cap, take note of the coolent level & top it up if needed. Start it & let it idle till it gets warm & then run it over 1000 rpm for a few mins, let it idle down a minute & bring it back up over 1000 rpm. Do this until it gets to normal operating temp & then a few mins more. Air rises so we're trying to burp the system.
If after doing this the coolent level is down from where it was when you 1st looked in/topped up, you've burped the system. If it's at the same level, I'd replace the stat.

 

Thanks for the info.

Whet out to check under the hood and I must have a large leek. There is coolant all over the cross member, but I can not pin point where it is coming from. The lower rad hose looks bad but I do not see a leak. What is the best way to view the weep hole? Guess I need to get a tester.

 

Could be leaking from the stat housing & running down the engine.
Wash the engine, drive it to temp & leave it idling while you look for the source of the leak. Just make sure the rad is topped up beforehand.

 

Found my leak, the water pump now has a steady stream of coolant dripping out of it. Going to replace it, the t stat and the lower rad hose (upper looks good).

Is there anything else I should replace while I am changing the pump?

 

Aside from all new coolant, you may want to back flush the cooling system before changing the pump.