The victim is a '89 740 Gl sedan with 101k miles which I purchased on Ebay for parts. Among its problems is a punctured radiator caused by a seized water pump. I replaced the pump with a used one from a 86 Turbo 740. Yes I know, but the price was right. After having the radiator repaired, I reinstaled it and the used water pump. Filling the radiator with water,(why waste $ when I am still evaluating the car as a daily driver) I started the engine. It immediately sprang a leak in the radiator. Much to my surprise the leak was in a new spot and not where the repair was made. I had it repaired again...(Tony's Radiator Shop in Holyoke, Ma) did not charge for the return repair. When I tried it again, I ran the motor without the cap on the expansion tank. Coolent (water) gushed out. I smelled the water for hydrocarbons. None were detected. The motor ran OK with a clear exhaust. The water continued to gush out until a gallon was expelled. I put my hand over the Expansion Tank fill port and could detect no pressure.

So what is causing this? All help will appreciated, John