Originally Posted by Contraman
1. With the out hose disconnected from the impeller, what kind of flow should you be getting from the impeller. Should it shoot out- an inch or so? Mine dribbled out? Steady dribble but not very impressive.
Depends on where the end of the hose is held. If you are very close the level of the boat's waterline then flow will be very little. However, if the end of the hose is below the waterline by more than 6 inches (15 cm) or so you should get a full-hose flow. If you're not, and you've cleaned the strainer etc., then could be fouling of the intake under the boat. Intakes are hard to anti-foul and typically get a lot more growth than the rest of your bottom.
If you suspect the intake, you can try a garden hose connected to it and try to push water (and growth/garbage) out the other direction but if it is hard growth (barnacles, etc.) then the only option is to chip them out. On our boat from inside with the seacock wide open you can slide a round dowel (just a little smaller than the pipe diameter) down through the seacock to dislodge things. If you wrap a rag around things as you work you don't get too much water in the boat. This will only work if the seacock is full-port (i.e. has an opening the same diameter as the pipe) and if you aren't timid. Last thing you want is to end up with a seacock you can't close. The other option is to jump in with a mask and snorkel (or haul the boat) and work from the outside.
If you do clean the intake, make sure you run plenty of water through it and the hose into a bucket so you clear any debris before running it into your engine.
2. Should you be able to blow on the out hose from the impeller and force water through the engine block(yes, this is a raw water cooling system on the 5411)? I was unable to do so even with the engine running and gave up when I could feel some heat on my lips!
Don't know your exact engine, so grain of salt, but all raw water cooled engines I am familiar with have a bypass for water flow. Since the water is intended to also cool the exhaust, and since the pumps are positive displacement
, they have a bypass to move the water to the exhaust when the thermostat is not calling for cooling in the block. In that case you should be able to pass water regardless of engine state/temperature. Be careful in all of this testing, the last thing you want to do is fill up your exhaust system with water and have it flow backward into the engine, through the open exhaust valve(s) and into the cylinders.