Water Pump issues

This week I launched my 78 FN and have a water pump issue. Here is what I found so far. I rebuilt the water pump (The big one that draws raw water) and replaced a blown seal, replaced the impellar). The water pump does't leak now and so I went out and ran the boat. At first I forgot to open the valve and the engine began to overheat when I got on the throttle. I then remembered to open the valve after seeing a little smoke from the overheated wet exhaust hose. The boat would not draw water when on a plane at all. It seemed to do fine when at a idle. We putted back the few hundred feet to the ramp and took another look at it. We took off the main water pump and found out it was shot so we replaced it (the one mounted on top of the engine) (the 78 engine had a 68 water pump on it?) As a result of the first overheating, when we went to start it the starter seemed to get stuck sometimes and the engine would try to bump the shaft even though it was in Neutral. We ran it again today and when we idled it ran ok, but again when we went to get on a plane it would not draw water through the hull to the engine. The hoses are hooked up correctly to the first water pump which is clearly marked In and Out. The hoses are clear of obstructions because when I hook up the hose to the back and open the valve water shoots through the bottom, when I have it closed it shoots thgrough the engine and out the exhaust. Everything in my mind says I put the impellar in backwards but someone told me that doesn't matter because it would snap the fins into the right way. It doesn't seem like it would to me. Which way would you put the impellar (fins pointed to the starboard or port. The engine is a right hand rotation, with the main crank shaft rotating towards the starboard side.) Anybody have a clue as to whats going on?
                                    Capt Duane

I have had a number of people tell me that the impellar would snap the fins in the right direction, so I have to push the "I believe" button on that one. My Grandpa had an old 1" gate valve,(spigot like for a hose)on there for the freshwater washdown to close off the raw water, so I thought that may be the problem(besides the fact they are illegal), but when I took it out it worked perfectly... but anyways I replaced it with a SS Ball valve. Now everything points to a $3.99 part (the thermostat).. It seems that it is stuck shut when we ran it on the lake, as there was no water coming through the exhaust, either that or the water turned to steam before it could exit the exhaust pipes. I know because the old wet exhust hose melted away from the exhaust manifolds and there was no water exiting the pipes when at idle. Whenever we run the cold hose water through it, it makes it out of the exhaust just fine. I took off the water pump that circulates the water inside the engine and found out that was shot, so I replaced that. Tomorrow I am going to pull the thermostat out tomorrow and test it with a lighter to see if it will open. I will replace it with a new one anyways while I have it out. If I replace that and it still doesn't work, I am out of answers.

Here is what I found:
Apparently the impellar was backwards because that was the first problem, it was broke into a couple pieces and jammed with the fins against each other inside. Everyone who says you can install the impellar backwards and have the fins snap the other way can prove it on their own boat. And I was going to replace the thermostat, but there wasn't one to begin with. My grandpa says he hasn't run one for as long as he can remember. Told me to check the book and if it says anything about a thermostat, then install one. Otherwise, it is not necessary. Thoughts on this? Keep in mind I know they install one for a reason, but I am not going to go putting one in just because someone says to do it. I listen to valid reasons and do my own research, then make my own determination. What would running the boat without a thermostat do? Gary S, not sure about the type of pump, can't find one like it, and its a starboard rotation engine, '78 chevy 350 OMC.    

was the shaft seal replaced? they will pull air through that area and cause an overheat. air is thinner than water and will be pulled first if you have a suction leak...it may not leak statically while sitting.
The shaft seal is one of the most overlooked problem creators
you do need a t-stat as Larry is indicating

75 Tique,
Thanks for the info. I learn so much from this site and other Nautique owners like yourself. Yes, that's my pump, (except mine is a lemon yellow, not the traditional Chevy Orange). That sucks (or not) about your pump not working even when you were gravity feeding it. So, I dropped off the pump last night to a guy named Jack, a friend of mine from the trailer park. He is supposed to be one of the best free lance boat mechanics near Tampa. I'll let you know. He said "We have the technology, we can rebuild it faster, stronger." Hopefully it wont be the $6 mill pump. More like $60 for parts and labor. The liner, impellar, and gaskets are being replace. It should be good to go now. Once I install it, I am sure that will be it with the pump issues. Now, for the next problem, but I will start a new thread if I encounter it.

SemperFIsh wrote: As a result of the first overheating, when we went to start it the starter seemed to get stuck sometimes and the engine would try to bump the shaft even though it was in Neutral.                                     Capt Duane

Thanks