So Fix it

Open your vehicles passenger side door and open the glove box.

Examine the inside of the glove box for a small sticker containing a series of codes. These regular production option, or RPO, codes catalog exactly what options you have installed on your truck. Each code contains three characters; the first two characters of the code will utilize letters, while the remaining character will be a number.

Check through each set of codes for "M30", "M50" or "MW2". The "M50" code represents a New Venture Gear five-speed manual transmission, available on 4.3-liter V-6 equipped models; the "MW2" represents a New Venture Gear five-speed manual transmission available for the 2.2-liter four-cylinder engine. Vehicles that features the "M30" RPO code have a GM 4L60-E for speed automatic transmission installed, available on both 4.3-liter and 2.2-liter models.

Disconnect the battery cable from the negative terminal on your Blazers battery. You need to do this any time you are completing a repair on your vehicle to reduce the chance of receiving an electrical shock.

Place a bucket under the radiator and drain the coolant from the cooling system. Typically, the drain plug is located at the bottom center of the radiator.

Remove the coolant hoses leading from the heater core to the engine. These are on the engine compartment side of the heater core. Plug the tubes of the heater core with a shop rag to reduce the chances of spilling coolant inside the vehicle when you remove the heater core.

Remove the heater core case located inside the passenger compartment. This case is located under the dashboard, just to the right of center of the vehicle. To do this, turn the screws connecting the heater core cover to the cowl counterclockwise and remove them.

Remove the support brackets from the heater core and remove the core from the passenger compartment side of the firewall.

Install the new heater core into the firewall. Be caul when you insert the tubes through the firewall so you dont bend them.

Install the support brackets and the heater core cover. Replace all of the retaining screws and turn them clockwise to secure.

Connect all hoses leading from the engine to the heater core inside the engine comparment, fill the radiator with coolant and reconnect the negative battery terminal.

Let the engine cool completely.

Remove black plastic air duct on the left side of the engine by separating it from the intake hose. In most S10 models built between 1998 and 2003, including the 2.2L version, you need to loosen a few clamps with a screwdriver to pull the air duct off the hose. In some models, the air duct is just stuck on the hose and comes off when you pull hard enough.

Locate the throttle to the left off the valve cover. Pull the cable to unsnap it from the bracket.

Pull the brake booster hose from its point on top of the valve cover.

Remove the valve cover bolts by using the ratchet, the extension and the socket set. There should be eight No. 10 bolts.

Take off the valve and scrape out the old gasket, which most likely will be hard from wear. Make sure no residue of the old gasket is in the mold. Clean the mold with a rag and wipe off gunk and dirt that might be stuck.

Place the new gasket in the mold, making sure it fits tightly. Reassemble the other components in the same order you disassembled them.

Open the hood of the truck and locate the battery on the passengers side of the truck. Loosen the clamp bolt on the negative battery cable end with a wrench.

Lift the negative battery cable off the negative battery terminal and isolate the cable away from the battery. Loosen the clamp bolt on the positive battery cable end with a wrench the lift the cable off the battery.

Isolate the positive battery cable from the battery terminals while you work. Since the cables are no longer connected to the battery, they can be secured away from the battery together with no risk.