hey does anyone know about how long it will take to change out my heater core on a 96 blazer all i can smell inside is antifreeze so im assuming thats the problem.

 

I changed the core in my '88 Jimmy (S-15 like a Blazer) and it was a breeze. The initial instruction 'remove the dashboard' was intimidating but turned out to be a snap. The secret is to locate all of the dash mounting screws (like the ones under the defroster grill). If you've got a manual, they should be well identified.
The one difficulty I had was that the core nipples on the replacement were slightly different shape than the originals. Hold the old & new cores side by side and reshape the new nipples to match the old ones. Otherwise they won't fit through the firewall.
Good luck.
PS I'd tell you where the mounting screws are but I don't know for your year. They're aren't as many as you'd expect. Even dropping the steering column was easy. If you've got an air bag, be sure to disconnect it and the battery.

 

I had to replace my heater core in my 95 Blazer and it took me about 4 hours. My suggestion would be to pull the old heater core out first and take it with you to the auto parts store and compare the inlet/outlet to the new unit and try to find one that is aligned the same, because moving or reshaping the inlet/outlet tubes can damage the new heater core since they are only crimped in with sealer behind them. Be very careful not to force anything because you don't want to have to do it twice.

 

For a 96 you'll have to remove the entire dash. Remove all the kick panels, the stereo, hvac control panel, drop the steering column, remove the 4 bolts in the front of the dash and rock it back to access the wiring harnesses, unplug harnesses, remove dash from vehicle. Once the dash is out, you'll see the heater core bolted to the firewall, behind a plastic cover. You'll need a 5.5mm socket to remove that plastic cover. Once the cover is off, it's just 2 big spring clip brackets holding it in place. Swap it out and put everything back together again. I think it took me somewhere in the neighborhood of 3-4 hours to do this on my 96 Jimmy. It's not hard, just alot of stuff to remove. In terms of tools, all you'll really need is a 1/4" drive socket set and a 5.5mm socket.
That's not step-for-step, that's just the gist of it to let you know what you're getting into.
Good luck.