Today I was going to put my boat in the water since the weather is finally breaking here in Rhode Island. I just had my closed cooling system installed so when we tested it on the trailer it wouldn't pump water out of the exhaust. The connection on the drive was good and nothing would pump out. We tried to run water through with the engine off and still got nothing. This all worked when I ran the boat 2 weeks ago without the closed system installed. Everything seems to be connected right and it is a half system not a full so the block should have been the only part that doesn't get fresh water. Is the impeller shot all of a sudden or is it something more complicated? The lower leg comes off to check the pump in the drive tomorrow. The motor is a gen V 502 mpi with a bravo 1 outdrive. Any ideas?

You should have a raw water pump installed on the engine as part of the fresh water cooling. You're putting water only to the outdrive impeller, you need to Y off the hose and also put water at the raw water pump. You will have to remove the intake hose from the thru hull under the engine and shove the garden hose into it.
Unfortunately you will also have to replace the raw water pump impeller which you ran dry.

"We tested it on the trailer" Does that mean you had a hose and earmuffs on it, or you actually were backed in at the launch?? Bravo 1's really need a good earmuff and hose pressure to get things going on the trailer. If you were backed in at the launch and the water level outside the boat was to where it was ready to float off, then you have a plumbing problem.
O.T.- Paul Sawyer, who was from western NY, was (I think) the first to push a 266 hydro to over 100 mph in one of the first "prop riders". His boat was the "ALTER EGO"!

If your drive is a Bravo, the sea water pump is on the engine, not the drive.. At least to the best of my knowledge..

I had the hose and earmuffs on the trailer. tomorrow we are planning to float it off the trailer to see if it pumps. the added pressure from being totaly immersed might be what it needed. I didn't realize I had to run water to the raw water pump. That will be the new project replacing that impeller. I'll have to wait until tomorrow. Thanks for your help!!