Trying to track down a leak associated with the pump in (I think) live well pump on a new to me boat.
I pulled the cartridge out of the Johnson pump and there are no obvious signs of cracks in the pump housing but could be hard to see if it is minor.
This pump is very close to the transom and the leak could be where it goes through the transom. There is a plastic screen on the wet side of the lower transom where the water enters. Volume of water is estimated to be about 1 gallon per hour on the leak. Any experience with this or suggestions?

No more water leak threads!

I've written quite a bit on the logic and method for finding leaks. So many people put the boat in the lake and then try to locate a leak. The key is to do the process BACKWARDS - put the water INSIDE THE BOAT at home and look for where it comes OUT as the boat sits on the trailer.

It may be appropriate to test the livewell system for leaks first. Fill the livewells with water and run any recirculation pumps to determine if water ends up in the bilge from the recirculation system. Next, plug the various fittings from outside the transom, then open the livewell drain(s) to allow water to fill those hoses for a leak test. Overfill the livewells intentionally so that the overflow hoses fill with water to test them. If livewell fill pumps have their own fittings on the transom, insert a garden hose into them from outside the transom and look for leaks inside the bilge as water pressure from the hose pushes water into the livewell system.

For general waterproof tests for all transom fittings, disconnect the battery or otherwise disable any automatic bilge pump and plug the bilge drain as you normally would before launching the boat. Watch for leaks outside the transom as you add water to the bilge until all of the low fittings in the bilge are submerged.

If the above doesn't identify a leak, consider that the leak COULD be at the cap/transom joint. In this case, water can be leaking in in the vicinity of the rubrail that gets submerged on many boats when simply floating. Test for this by using ample amounts of water from a running water hose held against the lower rubrail cap joint.

Don�t forget the water pressure gauge tube that runs from the engine to the gauge. I had a leak that was kicking my butt. I filled the boat with water as suggested and found a small leak around a thru the transom drain fitting but only about a half pint overnight . It finally became apparent to me that it was only leaking the gallon or two an hour while the boat was running. I pinched off the w.p. tube in front of the motor and the leak stopped. The tube was split up under the deck about an inch long.

Good point, Po Boy. That's the old school approach for W.P., but it's on a lot of boats out there. I discovered my Mercury has a pressure transducer on the outboard and an electrical circuit driving a gauge to show W.P. As a side note, the dang thing isn't working so well, so now I have to diagnose what's wrong.....

Thanks Flippin-Out, I have save your comments in MS Word. So I can refer to it when I get my boat back from the motor being serviced. I have noticed a leak lately when I never had one before other than a few drops. Will got thru your process when I get my boat back and the it warms up outside.

What kind of boat?

Many leaks I have found, the only way I find them is to get all in the bilge area where you can see the pumps and valves, back boat into the lake, turn pumps on and start looking. The control valves crack and pumps leak that you will never find putting water in the boat.

Thanks for the input. Bob, the boat is a Bass Cat.
Temporary setback with Flu but will follow the advice given!