Heater core is leaking

It can be bypassed. But the vehicle will no long produce heat for the occupants, nor will it be able to defrost your windshield. Which is a pretty mission critical component this time of year! At least up here in Montana it is. If you are in a warmer climate then go for it, if not I'd change out the heater core now. ALTHOUGH if you are dead set on bypassing it, here is the process :

Step 1: Remove Air Conditioning Grating or Dash Board Cover

In order to get at your heater core, you may need to take off the dash board cover, but if your air conditioning gratings are in the right place you may be able to get away with only removing the gratings. It depends on which heater core is leaking and whether it is directly behind the grating or not.

Step 2: Remove Hoses

There are two hoses that run into the heater core, one for anti-freeze to go in and one for it to go back to the engine. If these hoses have clamps, you can easily remove them. Otherwise, you will have to cut them. If you have to cut them make sure to do it as close to the heater core as possible so as to maximize the remaining length of hose you have to work with. Do not start working with the heater core while it is still hot; wait until the engine has been off for a few hours.

Step 3: Connect the Hoses Together

Use a hose connector or hose coupler to attach the two ends of hose together. That way, the anti-freeze that would be routed through the heater core will instead just go through a short loop of tubing. You can buy hose connectors or hose couplers in a hose repair kit at any auto supply store.

This is a relatively complex process, but it WILL costs hundreds of dollars to have a professional do it for you.