77 Merc 500 pumping but no tell tail

[hotrod53]

I’m getting a slight dribble sometimes. I have a new impeller and it appears to be pumping. I can push a weed wacker string 16” up the pee hole, it was formerly clogged by mud daubers. If we blow air in the pressure port hole near spark plug 2, we get air coming out of the copper water line and we can blow air and hear it at the prop, but no air at the tell tail.

There appears to be no water leaking inside of the cowl. Any suggestions of where it could be blocked or a method to clear it?

 

[Chris1956]

Gee, the telltale is usually supplied by a 90* elbow on the cylinder head water jacket. Pull the hose off and see the water stream. If none, you have a problem with the impeller/water pump of some kind of serious clog in the cooling passages.

 

[Berdink]

I’m getting a slight dribble sometimes. I have a new impeller and it appears to be pumping. I can push a weed wacker string 16” up the pee hole, it was formerly clogged by mud daubers. If we blow air in the pressure port hole near spark plug 2, we get air coming out of the copper water line and we can blow air and hear it at the prop, but no air at the tell tail.

There appears to be no water leaking inside of the cowl. Any suggestions of where it could be blocked or a method to clear it?

When was the last time you replaced the impeller?

 

[99yam40]

I would blow compressed air up the TT while running on muffs or in a tank of water to see if that moves the blockage around more to clear the TT

 

[Jeff J]

I hate to ask but are you sure the water line got connected to the lower unit properly or that the seals were installed for that connection?

 

[Berdink]

When was the last time you replaced the impeller?

Oops sorry, I see you posted you have a new impeller.

 

[Texasmark]

The tell tale circuit is normally off the exhaust manifold cooling water jacket (on my engines). Next time you run the engine, put your hand on the water jacket cover and see if it's cool to slightly warm. If so, fine. If hot you have a clog in that cooling system. Since cylinder heat is generated any time the engine is running, if the engine is running the water jacket has to be cooled. Therefore the water jacket cooling is a separate circuit and independent of what's going on in the rest of the engine.
If you disassemble down to removing the connector between the jacket and the cooling hose and get no water with the engine running, remove the adapter and stick something down in the hole to ensure it isn't clogged. If not, and no output, and the plate is hot, time to shut off the engine, remove the cover and plate, and find your passage clog.

When you replaced the impeller, what did the old one look like? Blade tips bent over and scrape lines in the rubber where it rubbed against the pump housing? Normally what you find. Any pieces of the impeller missing? If so, that could be the problem with your exhaust cooling circuit.