Hi trey5seven. Welcome to the forum. That's the water pump bypass hose. The fitting rarely corrodes away like that so you should be able to find one in a salvage yard. Getting the old one out will be the hardest part of the repair. They are usually made of brass so you can't weld a nut to it. It will probably crumble if you use an Easy Out. The best solution might be to drill it out and retap the hole. If you take the replacement fitting to an auto parts store, they should be able to match it up with the correct size tap. It will likely be pipe thread.
Before you drain any coolant, you might consider using a cheap digital voltmeter to test the coolant for its acidity. Place one probe on ground and the other probe in the coolant in the filler neck. I can't remember what the magic number is but the higher the reading, the more acid has built up in the system. The coolant normally becomes acidic over time. Any two different metals and an acid causes galvanic action, (a battery), which leads to corrosion. The cooling system has parts made from brass, copper, aluminum, iron, lead and tin. I would have to think the previous owner didn't change the cooolant on a regular basis to remove the acids. Also, new antifreeze has additives for corrosion protection and water pump lubricant that wear out in about two years.
Sunday, June 13th, 2010 AT 2:32 PM