Using a pour-in sealer will be a lost cause, but if you're really determined to try, "Bar's Leaks" is the only one to use. It's a chocolate-brown liquid with what looks like a bunch of rabbit poop in the bottle. Pour it in, top off with water, and go for a drive long enough to get the coolant up to full operating temperature. When (if) the leak seals up, drain the cooling system and do a quick clean water flush to get the rest of the stuff out, or the coolant will stay a nasty-looking milky color. Refill with a 50/50 mix of antifreeze and water.
Jerry
