Lost water pressure

[Likesspace]

Hi guys,
I have a "Tracker" 50 hp, 4 stroke, bigfoot outboard, (approx. year 2000), that I'm having some problems with.
All of a sudden I've lost water pressure. The tell-tale shows some signs of water movement but the flow is drastically reduced from where it once was, (I did have a strong stream and at WOT my psi gauge would read 13-15 psi.)
My family and I took the boat out one day and everything was fine. The next time we went to the lake I noticed that I was getting zero reading on the p.s.i. gauge and the flow was really low. This is at idle.
After the motor runs for a bit, the flow restricts even more until it eventually reaches the point that there are only droplets exiting the tell-tale. I've not moved it from the dock because I don't want to damage the motor.
I have advanced the throttle to approx. 3500 r.p.m.'s and the gauge still shows zero water pressure and the flow is still very low.
I guess I'm asking what could cause this to happen, literally, overnight?
The boat went from behaving perfectly to having this issue.
I checked under the cowling today and see that my p.s.i. gauge tubing tees into the tell-tale tubing so there's not much doubt that the problem is related.
My first thought is that the water pump impeller has gone bad but for that to happen overnight seems odd.
I'm thinking that there could be a blockage somewhere within the gauge/tell-tale tubing but I'm not sure how to go about diagnosing the problem. Right now I'm thinking about shooting some compressed air through the tubing, (from the gauge side to the motor side), but I don't want to damage anything by doing this.
I've also thought that there might be a break in the tubing. If that's the case then I'm thinking about running the motor on muffs to see if I can fine a leak.
I'm just looking for some advice from those who have much more experience than I have. I basically know how to change my fluids and plugs....beyond that I'm at a loss when it comes to outboards.
One more thing.....It's my understanding that this "Tracker" motor is actually a Yamaha in disguise, even though it was sold as a Mercury. Because of that if this needs moved to the Yamaha forum, please feel free to do so.
Thanks in advance for any help you guys can give me.

Dave

 

[Texasmark]

Put the engine on muffs and turn on the water pressure. Disconnect the water pressure/tell tale hose at the hose barb on the engine block that feeds engine block water (pressure) to the dash gauge and tell tale. Take a piece of wire and clean out the hose barb...determining that it's not temporarily blocked. Start the engine and run long enough to get a data point. You either get water squirting out or you don't. Go from there.

 

[racerone]

First step is a new impeller !-----How long have you owned it?-----Most motors should have a new impeller installed every 5 years.

 

[Likesspace]

Thanks for the replies, guys.
I know that I'm going to install a new impeller since it has been 3 or 4 years since it's been done. I'm just convinced that there is another problem since this literally happened overnight. I'll try what Texasmark said to do and go from there. I've pulled the boat out for the winter so I have plenty of time to work on it. Hopefully I can find either a split in the tubing or a clog. If I find either I'll probably just replace all of the tubing along with replacing the impeller and the thermostat.
Thanks again for the replies.

 

[Texasmark]

I went after a clog because of what you said. What could have happened, with you not indicating that your impeller is 4 years old and is of unknown operational/storage history, is that a piece of an impeller blade could have broken off and is clogging a water passage. Or you could have gotten into a mess of coontail moss or such as you were retrieving your boat the last time out. That being the case, what I did post would alert you that you have a clog or you don't have a clog.......Point you in the right direction for your search. If you have a clog, changing the impeller won't solve that problem necessarily.

 

[Likesspace]

I went after a clog because of what you said. What could have happened, with you not indicating that your impeller is 4 years old and is of unknown operational/storage history, is that a piece of an impeller blade could have broken off and is clogging a water passage. Or you could have gotten into a mess of coontail moss or such as you were retrieving your boat the last time out. That being the case, what I did post would alert you that you have a clog or you don't have a clog.......Point you in the right direction for your search. If you have a clog, changing the impeller won't solve that problem necessarily.

Texasmark...
Your assessment was correct. I disconnected the hose going from the tell-tale to the tee fitting that leads up to the psi gauge. I used weed eater string to make sure the hose was open from the tell-tale opening to the tee fitting. I then used the string to plunge from the tee into the 90 degree fitting that screwed into the block. I plunged several times into the block and once all was reconnected I was getting a good solid stream out of the tell-tale. In fact the stream was stronger than I've ever seen while running the motor on muffs. Unfortunately I did not think to verify that the psi gauge was once again, reading pressure. So tomorrow I'm going to make sure that I have a reading at the gauge and then I'm going to service the motor for the winter and get the boat cleaned and covered. I'll decide next spring if I'm going to tear into the lower unit and replace the impeller. It's not a job that I've done so I'm a little worried about undertaking the job. If you have any advice to make the job go easier, I'd love to hear it.
Thank you so much for your help.
It's great to have access to people who are willing to offer their expertise when a question is asked.
Have a great weekend.
Dave

 

[Texasmark]

Main problems you hear about are:
Before you start, a manual would help in addition to what I am posting....iboats sells them as does ebay.

1. Separation of the lower unit could be 4 obvious bolts between the LU and mid section. You may have a 5th bolt so mark the position of your zinc trim tab under the rear of the AV plate, pop the plastic cap on top of the midsection just above the trim tab and using a hex socket wrench remove the bolt holding the trim trab. Then look up inside the hole that was uncovered when the tab was removed and remove that bolt...#5.

2. Be careful prying on any aluminum surface in separating the LU...you can break off pieces of alum housing.
3. Shift into N (my preference) prior to disassy. The shift shaft rotates for gear selection with N in the middle. The shift shaft is a short splined stub at the front of the LU/midsection. The LU is Male and the midsection is female. Ensure that joint separates as you remove the LU. It must be removed maintaining downward pressure on the LU male portion to keep from pulling the male out of the shifter cam follower in the LU which makes for a big mess getting it reinserted.

4. The manual will guide you through the water pump disassy/assy.
5. Grease the splines of the drive shaft and shift shaft with no grease on top of either shaft (keeps sections from mating to the female in the LU) when ready for reassy.
6. Ensure the shifter is still in the N position....rotate the prop and the drive shaft doesn't rotate.

7. Stab the drive shaft while ensuring that the cooling water pipe mates with it's receptacle in the mid section and while aligning the shift shaft mating. If you cannot get the last inch in mating, have someone rotate the flywheel while you apply upward pressure with your hands on the LU. When the crankshaft female spline lines up with the drive shaft protruding from the LU splines the LU will move on up against the mid section. As you did upon removal, start the 4 nuts as you attach the LU and chase them up the studs as you move the LU into the midesction. Don't forget the screw under the AV plate and you trim tab, set to the mark you made when removing.