How do i change the thermostat in my 96 blazer?

Hoe hot does the engine get in degrees F? Can you check for coolant flow through the radiator?
As far as your heater, are the heater hoses hot on a warmed up engine? The radiator fan works ok?
Does the coolant boil over, the coolant reservoir fill up in a hurry?

1989 Chevy blazer 4.3 won't start..I have ... - CarGurus

www.cargurus.com > Questions > Chevrolet > BlazerCarGurusJan 30, 2013 - 96 Chevy S10 Blazer with 4.3 L engine vortex will turn over but won'tstart. ... i a 93 k5 blazer 5.7tbi in cold weather it will not start, if i hook jumper ... was told it just needed a Fuel pump, I replaced the Fuel pump, and the Filter, ...

just turn it out of the valve cover some dont have threads then you just pull it out

Seems like your good to go...
http://en.wikipedia.org/wiki/Chevrolet_S-10_Blazer#Second_generation

Mighty be your heater coil or your thermostat is not opening up to circulate antifreeze also could be low on antifreeze. Is the truck still running at normal temp?

The only relay box I know of is in your glove compartment. Just went through changing a fuel pump in my 96 and finally located it in there. Dealer told me it was under the hood. Little black cover pops off and there are 3 relay's inside.

The thermostat is under the fitting with the upper radiator hose on. Remove the 2 bolts replace the thermostat, add coolant. Allow the engine to heat up with the radiator cap installed on the lock position not fully tightened. The air in the system will purge out into the reservoir. Fill the reservoir to the hot line when fully heated and no air is coming out anymore.

Your temp gauge is wrong, check your fuel filter, may be clogged up, then I would say there is a system leakdown in the fuel system. You may have a pump going bad in the fuel tank.

you should have no problem their pretty much the same tranny meaning that there both automatics with or without o/d or 4x4s.

try reverse and push the button